View Source Changelog

All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog and this project adheres to Semantic Versioning.

[0.18.0] - 2026-05-28

Raises the Elixir version floor to 1.16 and aligns optional dependencies with their current stable series. No changes to Bond's public API or runtime behaviour.

Changed (breaking)

  • Minimum Elixir version is now ~> 1.16 (was ~> 1.14). Elixir 1.14 and 1.15 are no longer supported. The floor was raised to resolve formatter drift (the (-> t) zero-arity typespec syntax introduced in 1.15.0) and to allow CI to run format-checking against the newest Elixir without a version pin.

  • Bond.PropertyTest requires stream_data ~> 1.0 (was ~> 0.6). The optional property-based testing integration now targets the stable 1.x release series. Users of Bond.PropertyTest must upgrade their own stream_data dependency to ~> 1.0 (current release: 1.3.0).

Internal

  • CI matrix now spans Elixir 1.16–1.19 / OTP 26–27; the 1.14 row is removed.
  • lint job runs on Elixir 1.19.5 (was pinned to 1.14.5 due to formatter drift; pin is no longer needed).
  • New dialyzer CI job runs mix dialyzer against Bond's own library code on Elixir 1.19.5 / OTP 27.2, establishing a clean Dialyzer baseline for the library itself (previously only the downstream consumer was Dialyzer-checked).
  • GitHub Actions updated to Node.js 24 runtime (checkout@v6, cache@v5).
  • credo updated 1.7.3 → 1.7.18; stream_data updated 0.6.0 → 1.3.0.

[0.17.5] - 2026-05-28

A patch release eliminating downstream mix dialyzer warnings emitted by Bond-generated code when the user's assertion duplicates a typespec-implied guard. Surfaced by a dogfood round in a real consumer (Photon) where every use Bond module produced one pattern_match or pattern_match_cov warning, forcing the consumer to suppress with @dialyzer :no_match per module.

Fixed

  • Lifted assertion defps no longer emit if/else inline. The truthiness check and throw-on-failure moved into two new Bond.Runtime.Eval functions — check_assertion/3 (used by @pre, @post, and @invariant) and check_value/3 (used by Bond.check/1). Each is defined as a multi-clause function matching false/nil/_, which prevents Dialyzer's caller-flow narrowing from killing the falsy clause when the user's expression is statically true (e.g. @pre is_binary(x) on a function @spec-narrowed to binary()).

  • Lifted-defp arguments are routed through a type-laundering helper. Bond.Predicates.__opaque__/1 (and __truthy__/1 for the ~> operator) use :persistent_term.get/2 to defeat Dialyzer's parameter-type propagation from the wrapper into the lifted defp. Without this, an assertion expression containing and/or/case (which expand to their own internal case) would still narrow under the wrapper's @spec, producing pattern_match warnings inside the user's expression itself — e.g. @post is_binary(result) and result != "" on a function returning binary() had a dead false -> clause in the and/2 expansion.

  • Bond.Predicates.<~/2 discriminator is laundered. The pattern-match operator's case expr do pattern -> true; _unmatched -> false end previously produced pattern_match_cov warnings when the user's pattern exhausted the @spec-narrowed type of expr (e.g. {:ok, _} <~ result on a function returning {:ok, integer()}). Routing expr through __opaque__/1 keeps the _unmatched clause reachable.

  • Bond.Predicates.~>/2 antecedent is laundered. The implication operator's if antecedent do !!consequent else true end previously produced a pattern_match warning on the else: true branch when the antecedent was statically true (e.g. is_binary(x) ~> ... on a binary argument). Routing the antecedent through __truthy__/1 keeps the else branch reachable.

Internal

  • Five new fixtures in integration/consumer/lib/contract_consumer.ex (TypedGuard and TypedInvariant) exercise every shape that previously warned: tautological @pre / @post / @invariant, ~> antecedent tautology, <~ exhaustive pattern. The existing downstream-Dialyzer CI job (added in 0.17.4) is now also a regression guard for this fix.

  • Generated-AST unit tests updated in test/bond/compiler/{annotated_function,assertion,invariants}_test.exs to assert that wrapper → lifted-defp call sites route every argument through Bond.Predicates.__opaque__/1 and that the lifted defps delegate the if/throw to Bond.Runtime.Eval.check_assertion/3 / check_value/3.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.17.4] - 2026-05-28

A patch release fixing two Elixir 1.18+ compatibility issues, surfaced by a new downstream-consumer integration test that compiles and Dialyzer-checks the code Bond generates into a using module. Also expands the CI matrix to five Elixir versions and eliminates a family of parallel-compile races exposed by Elixir 1.19's more aggressive parallel compiler.

Fixed

  • Invariant post-check no longer emits a struct case into user modules. Elixir 1.18+'s type checker (under --warnings-as-errors) rejects a case var!(result) with struct clauses when the function's return type can't be a struct — for example size/1 returning an integer — producing "the following clause will never match" warnings that fail downstream builds. The shape match moved into Bond.Runtime.Eval.check_struct_invariant/3, whose result is typed term(), eliminating the false positive. Runtime behaviour is unchanged.

  • Bond.Runtime.Eval.should_evaluate?/3 type-spec widened. The chain_defaults map's value type previously excluded :purge, but a function with no @pre/@post of its own (e.g. an invariant-only size/1) legitimately contributes :purge for those kinds. Dialyzer flagged the mismatch and cascaded into six spurious downstream findings for users running mix dialyzer on their projects.

Internal

  • Downstream-consumer integration test added (integration/consumer). A standalone Mix project that uses Bond is now compiled and Dialyzer-checked as part of CI. This is the test that surfaced the two fixes above.

  • CI matrix expanded from 3 to 5 cells. Covers every Elixir minor from 1.14 to the current stable (1.19), each paired with the highest OTP it supports: 1.14.5/OTP 25.3, 1.16.3/OTP 26.2, 1.17.3/OTP 27.2, 1.18.3/OTP 27.2, 1.19.5/OTP 27.2. Confirms the ~> 1.14 floor is accurate across the full matrix.

  • Parallel-compile races eliminated. Elixir 1.19's more aggressive parallel compiler exposed race conditions where Bond's internal BEAM files could be read before they were fully written to disk. Fixed by:

    • Extracting Bond.Compiler.CompileStateFSM.Server from compile_state_fsm.ex into its own file.
    • Extracting Bond.Compiler.AnnotatedFunction.Clause from annotated_function.ex into its own file.
    • Changing alias to require in bond.ex and compiler.ex to establish a complete compile-dep chain that Mix's parallel scheduler enforces.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.17.3] - 2026-06-03

A small additive release: _name and name are now treated as semantically equivalent in the consistent-naming check. Surfaced by a Photon dogfood round where the fallback-clause idiom (def f(_a, _b, c) paired with a contracted def f(a, b, c)) tripped the agreement rule unnecessarily.

Changed

  • Underscore-prefixed top-level names normalize against their unprefixed counterparts in Bond.Compiler.Clauses.canonical_names/2. _a and a agree at the same position; the canonical at that position is the non-underscored form. This matches Elixir's leading-underscore convention ("bound but intentionally unused" — the same parameter, just marked as not-used in the body).

    # 0.17.2 — `CompileError`: position 0 disagrees (`:_a` vs `:a`)
# 0.17.3 — compiles cleanly
@pre is_atom(a)
def f(a, b, c) when is_atom(a), do: {:ok, a, b, c}
def f(_a, _b, c), do: {:fallback, c}

    Wildcards (bare _, returned as nil from top_level_name/1) are unaffected — they continue to adopt sibling clauses' names rather than agreeing with _a directly.

  • Bond.Compiler.Clauses.referenced_param_names/2 treats both spellings symmetrically: a contract referencing a matches a clause binding _a, and a contract referencing _a matches a clause binding a. The intersection check is name-equivalent under the leading-underscore normalization.

Internal

  • 8 new unit tests in Bond.Compiler.ClausesTest for the normalization rules (agreement, all-underscored agreement, truly-different names still disagreeing, wildcard-vs-named-underscore distinction, both directions of referenced_param_names matching).

  • 1 new behavioural test in Bond.MultiClauseDispatchTest driving the Photon-style fallback-clause idiom end-to-end.

  • FAQ entry "How are multi-clause functions handled?" gains a paragraph on the _name/name equivalence.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.17.2] - 2026-06-02

A purely additive release narrowing the 0.17.0 consistent-naming rule from "all positions must agree" to "positions referenced by some contract must agree." Surfaced by a second round of Photon dogfooding where a trivial result-only contract on a four-clause shape-dispatching function would otherwise have required renaming every parameter across all clauses.

Changed

  • Multi-clause consistent-naming check is now per-position based on contract references. A contract that doesn't reference any parameter name imposes no naming constraint:

    # 0.17.0 — `CompileError`: position 1 disagrees on :game vs :league
# 0.17.2 — compiles cleanly
@post is_boolean(result)
def can_access?(conn, %Game{} = game, %GameFilm{} = film), do: ...
def can_access?(conn, league, conference) when is_binary(league), do: ...

    Bond walks every @pre/@post/@invariant expression's AST and collects bare-variable references, intersecting with the union of top-level parameter names across all clauses. Synthetic bindings (result, old(...) helpers, the invariant subject) drop out of the intersection automatically. Agreement is required only at positions whose canonical name appears in the resulting set.

    Adding a contract that does reference a disagreeing position re-engages the rule at that position — the CompileError fires exactly when (and where) a contract needs the consistency. Trivial contracts attach freely; shape-dependent contracts still need ~> for cross-clause uniformity.

Added

Fixed

  • Bond.Compiler.Clauses.rewrite_clause_params/3 now correctly rebinds the canonical name when a clause's top-level name differs from it. This case couldn't arise under 0.17.0's strict rule but does under the 0.17.2 relaxation (at unreferenced positions where the canonical is a generated bond_arg_<idx> regardless of what the user named the parameter). Without the rebind, the wrapper would reference an unbound name at the super-call site.

Internal

  • 13 new unit tests in Bond.Compiler.ClausesTest covering the AST walker (bare/remote/operator/old/subject references, the cross-clause candidate-name union, and the documented closure- variable false-positive case) and the relaxed mode of assert_clauses_agree!/4 (:all, empty, agreeing, disagreeing required-name sets).

  • 2 new behavioural tests in Bond.MultiClauseDispatchTest covering the Photon-shape relaxation and the re-engagement when a parameter- referencing contract is added.

  • FAQ entry "How are multi-clause functions handled?" gains a subsection describing the positional rule and the trivial-contract affordance.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.17.1] - 2026-05-31

A purely additive release closing a doc-symmetry gap: per-function @pre/@post already get rendered into each function's @doc as #### Preconditions / #### Postconditions sections, but module-level @invariant declarations had no rendered home. Readers landing on a struct module's docs page couldn't see what invariants the module ensures unless the author had hand-written them up.

Added

  • Auto-generated ## Invariants moduledoc section for any module with @invariant declarations. The section names the struct, explains the implicit subject binding (so readers without prior Bond context can read the assertions), lists each invariant in the same label: expression form used by per-function contract docs, and notes when invariants fire plus the defp exemption.

    ## Invariants

Bond ensures the following invariants hold for every value of
`%BoundedStack{}` produced by or passed into this module's public API.
Inside each assertion, `subject` refers to the value being checked.

    non_negative_capacity: subject.capacity >= 0
    size_within_capacity: length(subject.items) <= subject.capacity

These invariants are checked automatically on entry to and exit from
every public function in this module. Private functions are exempt by
the Eiffel convention.

    Special cases:

    • Users who already wrote a @moduledoc get the generated section appended after their authored content.
    • Users who wrote @moduledoc false have their decision respected — no section is added and the module remains hidden.
    • Users with @invariant but no @moduledoc get a moduledoc synthesised containing just the Invariants section, so the contracts surface in the generated docs.
    • :invariants set to :purge (compile-time disable) suppresses the auto-generated section, matching the per-function contract-doc suppression rule.

Changed

  • Bond.Compiler.ContractDocs.moduledoc_invariants_section/3 — new internal function producing the markdown section. Reuses the same label: expression formatting as the existing per-function doc generation so labelled and bare invariants render consistently across function-level and module-level contract docs.

  • Bond's __before_compile__ hook now augments the user module's :moduledoc attribute via Module.put_attribute/3 at compile-end, reading the current value and appending the generated section.

  • README's @invariant section gains a new "Generated documentation" subsection describing the auto-generation behaviour and the special cases above.

Internal

  • New test/support fixtures (BondTest.SynthesizedModuledocInvariant, …HiddenModuledocFixture, …PurgedInvariantsFixture) exercise the synthesised, hidden, and purge code paths. 17 new tests across Bond.Compiler.ContractDocsTest (unit) and Bond.ModuledocInvariantsTest (end-to-end via Code.fetch_docs/1).

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.17.0] - 2026-05-30

0.17.0 closes the longest-standing bug surfaced by real-world dogfooding: multi-clause functions whose first body clause had shape-specific patterns silently broke callers using a different shape. The fix is a per-clause wrapper redesign that preserves Elixir's natural multi-clause dispatch, plus a new rule that all clauses must agree on the top-level parameter name at each position when Bond is attaching contracts.

0.17.0 also fixes a latent semantic bug in Bond.Predicates.~>/2: the implication operator was a def, so both sides were eagerly evaluated. The natural "shape-dependent assertion" pattern (is_struct(x, Mod) ~> (x.id > 0)) crashed on non-struct inputs to the antecedent. ~> is now a defmacro that short-circuits.

Breaking changes (minor)

  • Bond.Predicates.~>/2 is now a macro, not a function. The expansion is if antecedent, do: !!consequent, else: true, so the consequent is only evaluated when the antecedent is truthy. This matches the logical reading of implication and makes shape-dependent assertions safe to write.

    # Was: both sides evaluated eagerly — `String.length(x)` raised
# FunctionClauseError when `x` wasn't a binary.
@pre is_binary(x) ~> (String.length(x) > 0)

# Now: `String.length(x)` is only evaluated when `is_binary(x)`
# is truthy. Same source, correct semantics.

    The migration impact is limited: code that passed ~> as a function capture (&Bond.Predicates.~>/2) no longer compiles. Use a function wrapper or the underlying implies?/2 (still a function and still eagerly evaluated) instead. The infix usage that's common in contracts is unchanged.

  • Multi-clause functions with contracts must agree on top-level parameter names across all clauses. Heterogeneous naming raises CompileError at the function's compile site. Pre-0.17.0 Bond used the first clause's params for the wrapper head verbatim, silently breaking callers whose shape matched a non-first clause; the new rule makes the constraint explicit and pushes naming consistency (often a readability win regardless of Bond).

    # Was (silently broken): callers passing strings hit
# FunctionClauseError inside Bond's generated code.
def lookup(conn, %Game{} = g, %GameFilm{} = f), do: ...
def lookup(conn, league, conference) when is_binary(league), do: ...

# Now: rename for consistent positional meaning across clauses.
def lookup(conn, %Game{} = resource, %GameFilm{} = scope), do: ...
def lookup(conn, resource, scope) when is_binary(resource), do: ...

    Wildcard clauses (def f(_)) and literal-pattern clauses (def f(0)) don't bind a top-level name at that position — they adopt whatever name a sibling clause provides. So the common def try_init(_)-paired-with-def try_init(capacity) pattern works unchanged.

    For shape-dependent assertions across clauses, use the ~> implication operator (which now short-circuits, per above). Per-clause contracts may be added in a future release if the consistent-naming restriction turns out to bite real code.

Added

  • Bond.Compiler.Clauses — new internal module owning clause- shape utilities: top_level_names/1, canonical_names/1, assert_clauses_agree!/3 (the validator), rewrite_clause_params/3 (canonical-name binding + underscore-prefix of unused names), and underscore_prefix_unused/2.

  • Bond.Compiler.ClauseWrapper — new internal module owning per-clause wrapper emission. Extracted from AnnotatedFunction (which is on the FSM's hot path) to keep that file small and avoid the parallel-compile race the project first encountered in 0.13.0.

Changed

  • Wrapper emission switches from single-wrapper to per-clause. For an N-clause user function, Bond now emits N wrapper clauses, each preserving the user's pattern (with destructured names underscore-prefixed where the wrapper body doesn't reference them). Elixir's natural multi-clause dispatch routes each call to the appropriate user clause via super/N. Wrong-shape inputs raise FunctionClauseError at the wrapper layer, matching the pre-Bond behaviour.

  • Lifted assertion defps' parameter heads diverge by clause count.

    • Single-clause functions keep the user's pattern in the lifted defp head, so contracts can still reference destructured names from the head (e.g. current_count from %__MODULE__{count: current_count} = state — the contracts-and-concurrency guide example works unchanged).
    • Multi-clause functions use the canonical top-level names as bare vars. Contracts can only reference those names; shape-dependent assertions use ~>.

  • Destructure-in-head wrapper warnings (the original #3 from the Photon dogfood) are silenced. Bond's per-clause wrapper now underscore-prefixes any destructured name the wrapper body doesn't reference. The lifted defp's pattern (for single-clause functions) still binds those names, so contract-side access is unaffected.

Internal

  • Bond.Compiler.Invariants simplifications. The destructure-only invariant handling that ran in 0.16.x is subsumed by the canonical- name rewrite — Invariants.rewrite_call_params/2 and Invariants.params_split/3 are no longer called from emission. They remain in the module for now; cleanup deferred to a later release.

  • Bond.Compiler.AnnotatedFunction shrunk from 448 → 430 lines via the ClauseWrapper and Clauses extractions, well below the historical baseline where the parallel-compile race surfaced.

  • Test fixture migration. The existing BondTest.InvariantSmoke. try_new/1 (wildcard adopts canonical) and BondTest.Stack.new/N (all clauses agree on capacity) work unchanged under the new rule. The unit-test fixture in Bond.Compiler.AnnotatedFunctionTest (previously list/map) migrated to consistent input.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.16.2] - 2026-05-28

A patch release covering eight issues surfaced by dogfooding Bond 0.16.1 on a real-world Elixir umbrella application (Photon, ~200+ modules). Six fixes bundle here; two (#2 wrapper-head shape leak, #3 destructure-in- head unused warnings) are deferred to 0.17.0 pending a design conversation.

Changed

  • Remote function calls are now valid as the outermost expression of an assertion. Pre-0.16.2, @pre String.starts_with?(x, "foo") was rejected by Bond.Compiler.Assertion.is_assertion_expression/1 — the AST's head is a {:., _, _} 3-tuple, not an atom, so the guard failed. Workaround was an == true suffix on every such assertion. The relaxed guard accepts the remote-call shape, including Map.has_key?(m, :k), Enum.all?(xs, &f/1), String.starts_with?(s, "prefix"), and Erlang calls (:erlang.is_atom).

  • No @doc emission on defp. Contracts on private helpers previously triggered Elixir's "@doc is always discarded for private functions" warning on every contracted defp, making the combination unusable without compile-time noise. Bond.Compiler.ContractDocs. doc_clauses/4 now short-circuits for :defp kind. The contracts themselves continue to fire — the warning was the only blocker.

  • Bond.Predicates moduledoc gains an "Operator precedence" section documenting the ~> / <~ left-associativity trap. A ~> pattern <~ B parses as (A ~> pattern) <~ B, where the LHS of <~ becomes an arbitrary expression containing _ and fails to compile. The fix is parens around the inner operator. Same trap surfaced as a boxed callout in the main moduledoc's Assertion Syntax section so readers see it before they fall into it.

  • Telemetry section gains a concrete metadata-map example showing the {name, arity} shape of :function, the sorted-binding-list shape of :binding, and a note on :assertion_id stability for aggregation pipelines.

  • Assertion Syntax section in the moduledoc now shows remote-call examples and explicitly notes which forms aren't valid (bare literals, bare variables, non-call expressions).

Fixed

  • @pre is_binary(x), positive: x > 0 (bare assertion mixed with a labelled one) and @pre is_integer(x), x > 0 (two bare assertions in a single call) previously fell through to Kernel's @/1 and died with "expected 0 or 1 argument for @pre, got: 2" — a confusing error that didn't point at the parse issue. Bond now matches these shapes at the macro layer and raises a clear CompileError suggesting either label-every-assertion (keyword-list form) or separate @pre/@post lines. Same catch-all added for @invariant.

  • Bond-shaped diagnostics on malformed assertions. When the user wrote an assertion that didn't satisfy is_assertion_expression/1 (@pre 42, @pre :foo, @pre "hello"), Bond previously surfaced a bare FunctionClauseError from Assertion.new/5 with a stacktrace that dumped the full Macro.Env. New Bond.Compiler.Assertion.validate_expression!/2 is called from both register_assertion/5 and register_invariant/4, and raises CompileError with the env's file/line, the expression's source (via Macro.to_string/1), and a one-sentence hint at valid forms.

Internal

  • Test coverage filled across each fix (+36 tests, 256 total):
    • 6 unit tests in assertion_test.exs for the relaxed AST guard plus the new validate_expression!/2 validator.
    • 8 behavioural tests in a new BondTest.RemoteCallAssertions fixture proving remote-call assertions work end-to-end in @pre, @post, @invariant, and check/1 — both success and violation paths.
    • 4 behavioural + diagnostic tests for defp contracts, including a capture_io(:stderr, ...) assertion that no @doc-discarded warning fires during compilation.
    • 9 behavioural tests covering the new bare-vs-labelled CompileError catch-alls and verifying all five existing valid forms still compile cleanly.

Deferred (to 0.17.0)

  • #2 wrapper-head shape leak. Bond's override head uses the first body clause's params verbatim, so multi-clause functions with a shape-specific first clause silently break callers using a different shape (a def fn(conn, %Game{}, %GameFilm{}) clause alongside a sibling def fn(conn, league, conference) when is_binary(league) clause will misroute string callers). The right fix needs a design conversation on whether to use a shape-neutral wrapper with restricted contract refs vs a per-clause wrapper that preserves dispatch faithfully.

  • #3 destructure-in-head wrapper warnings. When the first body clause has destructure like def f(%Mod{a: x, b: y} = z) and the wrapper body uses only z, Elixir warns about unused x/y. Partially subsumed by #2's resolution.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.16.1] - 2026-05-27

A patch release covering a 1.0-prep test-coverage audit (no behavioural change, just locking down behaviour that wasn't directly tested) plus a refresh of the supporting guides for content that had drifted out of date with 0.16.0.

Changed

  • guides/about.md — full rewrite. The previous version's feature TODO list still showed conditional compilation (shipped in 0.10/0.11) and invariants (shipped in 0.13) as unchecked items, and the framing read like marketing copy. New version is structured as "what Bond is, when to reach for it, background" — same length, every paragraph carrying information.

  • guides/getting-started.md — @invariant section added. The tutorial previously mentioned @invariant only in "Next steps." A reader following it linearly would never learn there was a third contract kind. New section between "Inline checks" and "Disabling contracts in production" introduces it with a BoundedStack example and the subject binding, then points at the moduledoc for the full reference. The intro line at the top mentions @invariant alongside @pre/@post/check/1. The disabling-in-production config snippet now lists :invariants (was listing three of four keys).

Fixed

  • guides/faq.md — "When does Bond check invariants?" description brought current. The previous text said destructure-only function heads (def foo(%__MODULE__{f: v}, ...), no = name) emit a compile-time warning and skip the pre-check. The 0.16.0 release lifted that restriction — Bond now rewrites the override clause to capture the struct under a generated name and the pre-check fires. Multi-struct heads are also noted (weren't previously).

  • guides/getting-started.md — dead anchor. The "Next steps" link to the Invariants section used the pre-0.16.0 anchor #module-invariants; updated to #module-invariant-for-struct-modules matching the renamed section.

Internal

  • Test coverage filled across seven gaps from a 1.0-prep audit (+16 tests, 220 total; all green). No behavioural change — each fill verifies behaviour that was already in place but lacked a direct test:

    • Invariant telemetry. [:bond, :assertion, :failure] fires with :kind => :invariant on invariant violations. Documented since 0.13.0; previously only the other three kinds had assertions on the event.

    • @invariant runtime modes. Two tests cover (a) put_env :bond, :invariants, false skips evaluation, and (b) flipping back to true re-engages it. The runtime-toggle path was tested for @pre/@post but not @invariant.

    • Compound and guards. Behavioural confirmation that is_struct(x, __MODULE__) nested inside an and guard triggers the pre-invariant check. (Compiler-level detection was already covered.) The or case is deliberately not covered — it's a latent unsafe pattern worth a separate design discussion.

    • No-struct heads. Behavioural confirmation that a function whose head doesn't expose the struct silently skips pre- invariant evaluation — passing non-struct arguments returns cleanly rather than crashing on a subject.<field> access.

    • Migration CompileErrors. The legacy @invariant <name>, <expr> and the two arity-2 check shapes (removed in 0.16.0) now have direct assertions that they raise CompileError with the migration message at the call site.

    • Bond.Test.assert_check_violation/2. The helper existed alongside its precondition/postcondition/invariant siblings but had no test.

    • old(...) runtime integration. Compiler-level extraction and precompilation were covered; the runtime path (does the snapshotted value end up correctly bound when the postcondition evaluates?) had no direct test. New Bond.OldRuntimeTest covers success and failure paths plus the captured binding() at failure.

  • Coverage audit findings worth keeping in mind for future releases (not addressed in 0.16.1):

    • Compound or guards containing is_struct(_, __MODULE__) are a latent unsafe pattern. Bond's detection recognises x as the struct parameter, but the pre-invariant fires unconditionally — so a runtime input matching a non-struct alternative crashes in the invariant body rather than raising a clean FunctionClauseError.
    • Relatedly, the override clause doesn't reproduce the user's function-head guard. Calling Smoke.reverse(5) (where reverse has when is_struct(stack, __MODULE__)) hits Bond's pattern-less override, fires the pre-invariant against the integer, and crashes inside the invariant body before super dispatches to the user's def for the proper FunctionClauseError.

    Neither issue surfaces in normal use (callers pass arguments of the right shape) — they're worth a fix pass before 1.0 but not shippable as a patch.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.16.0] - 2026-05-26

0.16.0 is the first 1.0-prep release. It tightens the public API in two places where the surface had accumulated friction: @invariant drops its required binding-name argument in favour of an implicit subject binding, and check/2 drops its two string-label forms in favour of check expr and check label: expr. Both legacy shapes now raise CompileError at the call site with a migration message.

Breaking changes (minor)

  • @invariant <name>, <expr> was removed. The new form is @invariant <expr_or_kw> — no binding-name argument. Invariant expressions reference the implicit subject binding, which Bond rebinds at every check site to whichever struct parameter the function head exposes (detected automatically across %__MODULE__{} = name patterns, is_struct(name, __MODULE__) guards, and %__MODULE__{...} destructures).

    # Was:
@invariant stack,
           non_negative_capacity: stack.capacity >= 0,
           size_within_capacity: length(stack.items) <= stack.capacity

# Now:
@invariant non_negative_capacity: subject.capacity >= 0,
           size_within_capacity: length(subject.items) <= subject.capacity

    Function bodies don't change — def push(%__MODULE__{} = stack, item) keeps its parameter named stack; Bond detects and rebinds subject to it automatically. The legacy 2-arg shape raises a CompileError with the migration message.

  • check/2 was removed. The two string-label forms (check "label", expr and check expr, "label") are gone — they were redundant with the keyword-list form, which already carries a label:

    # Was:
check "x is a number", is_number(x)
check is_number(x), "x is a number"

# Now:
check x_is_number: is_number(x)

    check expr (bare) and check label: expr (keyword) are the two remaining forms. The legacy 2-arg shape raises a CompileError with the migration message.

Added

  • Multi-struct heads in @invariant. def merge(%__MODULE__{} = a, %__MODULE__{} = b) now triggers invariant checks on both struct parameters in left-to-right order, with subject rebinding to each in turn. Previously only the first detected struct param was checked.

  • Destructure-only heads in @invariant. def head(%__MODULE__{items: [first | _]}) (no = name) now participates in pre-invariant checks. Bond rewrites the override clause head to add a capturing binding (%__MODULE__{items: [first | _]} = __bond_subject_0__) so the struct passes cleanly to the lifted invariants defp. Previously this shape was skipped silently with a documented (but unimplemented) warning.

    This also closes a latent bug in the override emission: super(...) previously spliced raw destructure patterns as expressions, which would fail at compile time on patterns like [h | _] if a user had ever tried it with @pre/@post. The capture rewrite passes the original input through cleanly.

  • Bond.Compiler.Invariants.detect_struct_params/2 — internal helper that finds every struct-bearing parameter in a function head, returning a list of {:bound, var, idx} or {:destructure, idx} descriptors. Replaces the single-struct find_struct_arg/2 removed below.

Changed

  • Doc-generation logic extracted into Bond.Compiler.ContractDocs. Pure refactor — no user-visible change. Shaves ~80 lines off Bond.Compiler.AnnotatedFunction, which is on the FSM's hot path. A shorter AnnotatedFunction reduces the window for the parallel-compile race first encountered (and partially mitigated) in 0.13.0.

  • Bond.Compiler.Assertion drops the :binding_name field. The invariant body now hardcodes the subject = bond_invariant_value rebind. The struct shrinks from 8 fields to 7.

  • Bond.Compiler.Invariants simplified. Removed the legacy single-struct helpers find_struct_arg/2, struct_arg/2, pre_invariant_stmts/5, and the supporting AST walkers. New emission uses detect_struct_params/2 + all_pre_invariant_stmts/5 + rewrite_call_params/2 end-to-end.

  • Moduledoc reorganised. Sections regroup as "what you write" (Usage → Assertion syntax → @invariant → check/1 → old) then "how you operate" (Documenting contracts → Conditional compilation → Telemetry → PBT). The 0.10 → 0.11 migration table is dropped, and the long Agent race-condition narrative in old moves to the contracts-and-concurrency guide.

  • Telemetry :kind documentation updated to include :invariant (the event was already emitted since 0.13.0; the docs were stale).

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.15.0] - 2026-05-25

0.15.0 closes a correctness gap in conditional compilation: previously :preconditions, :postconditions, and :invariants could be toggled independently in any combination, including combinations that produced diagnostically-misleading errors (e.g. postconditions on while preconditions are off — a "postcondition failure" might really mean the caller broke their contract, not the function).

0.15.0 enforces the natural chain preconditions ≤ postconditions ≤ invariants both at compile time and at runtime. :checks remains independent of the chain.

Breaking changes (minor)

  • Compile-time validation of :purge combinations. :purge on a lower kind now requires :purge on every higher kind in the chain. Bond.Compiler.resolve_config/3 raises CompileError with an explanation otherwise.

    Migration: if you used config :bond, preconditions: :purge without also purging postconditions/invariants, choose one:

    # Was:
config :bond, preconditions: :purge

# Option A — also purge the chain (preserves the original intent
# if you wanted zero overhead):
config :bond,
  preconditions: :purge,
  postconditions: :purge,
  invariants: :purge

# Option B — runtime-disable instead of purge (keeps the code,
# operator can flip on at runtime):
config :bond,
  preconditions: false

    false is unaffected — runtime-disabling a single kind is unchanged. Only :purge participates in the compile-time check.

Added

  • Runtime chain propagation. When a lower kind is false at runtime (Application.put_env(:bond, :preconditions, false)), every higher kind is also skipped automatically, regardless of its own setting. Enforced in Bond.Runtime.Eval.should_evaluate?/3 via the new optional third argument carrying the compile-time defaults of every lower kind.

  • One-time-per-process propagation log. The first time a higher kind is skipped because a lower one is runtime-off, Bond emits a Logger.warning describing the chain constraint, the offending pair, and the Application.put_env invocation that would bring the higher kind back. Deduped per (higher, lower) pair via a Process-dictionary marker — long-running OTP processes get exactly one warning per pair.

Changed

  • Bond.Runtime.Eval.should_evaluate?/2 is now should_evaluate?/3 with an optional chain_defaults map; the 2-arity call still works via default and is unchanged behaviour-wise for :preconditions and :checks (both have no lower kinds).

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.14.0] - 2026-05-24

0.14.0 adds Bond.PropertyTest — a property-based testing layer that uses Bond's contracts as the oracle. The hard part of PBT is usually writing the predicate that distinguishes right from wrong outputs; contracts already supply that at every call site. PBT just feeds random inputs through already-instrumented code.

Added

  • Bond.PropertyTest.contract_holds/2 — single macro, two forms:

    • Form 1 (single function). contract_holds &Mod.fn/N, args: [gen0, ...] expands to a property block that calls the function with random arguments and lets Bond's runtime contracts fail the property on any violation. StreamData shrinks to the minimal counterexample.

    • Form 2 (module sequence). contract_holds Module, constructors:, transformers:, observers: expands to a property block that generates random sequences of operations over a struct module and runs them. State is threaded through transformers; observers don't advance state but the pre-invariant still fires. The module's @invariants are the oracle. Supports %Mod{} and {:ok, %Mod{}} return shapes; {:error, _} terminates the sequence cleanly. Common option :name overrides the auto-generated property description.

    The macro dispatches by first-arg AST shape (function reference vs module alias).

  • use Bond.PropertyTest — brings in ExUnitProperties and imports the contract_holds macro. Raises a CompileError at the use site with installation instructions if :stream_data isn't available.

  • Bond.PropertyTest.Sequence — internal helper module owning the sequence generator and runner used by Form 2.

  • New FAQ entry: "How does Bond compose with StreamData / property-based testing?".

Changed

  • :stream_data moves from only: [:dev, :test] to a regular dep with optional: true. Users who want PBT now add {:stream_data, "~> 0.6"} to their own deps; users who don't pay no cost.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.13.0] - 2026-05-23

0.13.0 adds @invariant declarations for struct modules — module-scoped properties that hold across every public function in the struct's defining module. Where @pre/@post constrain a single function call, @invariant constrains the struct itself.

Added

  • @invariant <name>, <kw_or_expression> annotation. Same shape as @pre/@post: a labelled keyword-list of assertions, or a single unlabelled expression. The first argument is the variable name the expression refers to (e.g. stack in @invariant stack, length(stack.items) <= stack.capacity).

    Invariants are checked at the boundaries of every public function in the module:

    • On entry, when the function head pattern-matches %__MODULE__{} = name or has an is_struct(name, __MODULE__) guard.
    • On exit, against the return value if it's %__MODULE__{} or {:ok, %__MODULE__{}}. Other return shapes fall through with no check.
    • Never for defp — private functions are exempt by the Eiffel convention (they often hold transiently-invalid state).

    When a function destructures %__MODULE__{...} in its head without binding the whole struct to a variable, Bond emits a compile-time warning suggesting %__MODULE__{...} = name to enable the pre-check.

  • Bond.InvariantError — new exception parallel to PreconditionError/PostconditionError/CheckError. Raised on invariant violation; carries the same metadata shape.

  • Bond.Test.assert_invariant_violation/2 — ExUnit helper mirroring the existing pre/post/check helpers.

  • :invariants conditional-compilation key. Joins :preconditions, :postconditions, and :checks. Same true | false | :purge value space; same runtime toggleability via Application.put_env/3; same :overrides and use Bond, invariants: … support.

  • Bond.Compiler.Invariants — new internal module owning the invariant emission logic (struct-arg detection, pre-/post-invariant call sites, the lifted invariants defp). Kept separate from Bond.Compiler.AnnotatedFunction for separation of concerns and to avoid parallel-compile scheduling issues with the larger combined file.

Changed

  • [:bond, :assertion, :failure] telemetry events now also fire for invariant violations, with :kind => :invariant in the metadata. No subscriber changes are needed — existing handlers attached to the event automatically pick up the new kind.

  • The internal Bond.Compiler.Assertion struct gains a :binding_name field, populated only on :invariant assertions from the declaration's first argument.

  • Bond.Compiler.AnnotatedFunction gains an :invariants field plus put_invariants/2 and has_invariants?/1 helpers. override?/1 widens to emit overrides for public functions in modules with @invariants, even when the function has no per-function @pre/@post.

  • Bond.Compiler.CompileStateFSM tracks module-scoped invariants alongside the per-function preconditions/postconditions. Invariants don't transition the FSM into :contracts_pending (they don't attach to a "next function") and aren't flushed by function definitions.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.12.0] - 2026-05-22

0.12.0 lands two internal-shape changes that compose on top of the 0.11.0 conditional-compilation work: contract closures move out of override clauses into named private functions on the user's module (reducing injected code per contract'd function), and :telemetry events fire on assertion failures.

Added

  • [:bond, :assertion, :failure] telemetry event. Fires once per contract violation — @pre, @post, or check — immediately before the corresponding Bond.PreconditionError / Bond.PostconditionError / Bond.CheckError is raised. Single event family for all three kinds; consumers filter on the :kind metadata. Measurements carry :system_time and :monotonic_time; metadata carries :kind, :module, :function, :label, :expression, :assertion_id, :file, :line, and :binding. See the new "Telemetry" section in the Bond moduledoc / README. {:telemetry, "~> 1.0"} is now a regular dependency.

  • Bond.Runtime.Eval.should_evaluate?/2 — internal helper that performs the Application.get_env/3 runtime guard. Used by the emission shape (see "Internal" below) to avoid allocating the assertion-evaluation closure when the runtime guard says skip.

Changed

  • Per-function assertion closures are lifted into named defps on the using module: __bond_preconditions__<fun>__<arity> and __bond_postconditions__<fun>__<arity>. The override clause itself is now a small wrapper that calls these via Bond.Runtime.Eval.evaluate_preconditions/1 / evaluate_postconditions/1. The big inline assertion-evaluation AST that used to be re-emitted into every override is gone; the BEAM carries one tiny override + one defp per non-purged kind, rather than the whole eval body inlined per function.

  • Runtime guard moved into Bond.Runtime.Eval. The override calls should_evaluate?(:preconditions, <compile_time_mode>) and only builds the assertion-evaluation closure when that returns true. The Application.get_env/3 lookup logic lives entirely in Bond.Runtime rather than being inlined at every contract'd function.

  • Bond.check/1,2 routes through the same throw/catch path as @pre/@post. All three kinds now produce {:assertion_failure, info} throws caught by Bond.Runtime.Eval, which fires the telemetry event and raises. This unifies the plumbing across the three kinds; previously check raised inline.

  • Stacktrace pruning now also filters frames whose function name starts with __bond_ (the lifted defps), so failures continue to point at the user's call site rather than into Bond-generated plumbing.

  • Benchmark on the project fixture (bench/runtime_check_overhead.exs, trivial @pre is_number(x) in a tight loop):

    mode0.11.00.12.0
    :purge~48 ns~34 ns
    true~155 ns~143 ns
    false~89 ns~91 ns

    The true path improves because the override no longer re-emits the full assertion-eval AST inline. The false (runtime-skip) path is flat within noise — should_evaluate?/2 short-circuits before the closure is allocated.

Fixed

  • Bond.CheckError's message/1 no longer crashes when the error's :function metadata is missing (regression introduced and fixed internally during the check plumbing unification).

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.11.0] - 2026-05-21

0.11.0 reshapes the conditional-compilation config introduced in 0.10.0 around a new value space — true | false | :purge per kind — and adds two new features that compose on top of it: runtime toggling without recompilation, and per-module overrides.

Breaking changes (minor)

  • config :bond, <kind>: false no longer compiles contracts out. It now means "compiled in, runtime guard defaults to off." If you used false in 0.10.0 to get zero-overhead behaviour, change it to :purge to preserve that behaviour. true continues to work as before (with the addition of runtime toggleability — see below).

Added

  • :purge mode for each contract kind. Setting any of :preconditions, :postconditions, or :checks to :purge causes Bond to emit no code for that kind. The resulting BEAM contains no contract logic; per-call overhead is zero. Contract documentation for that kind is also suppressed.

  • Runtime toggling. When a kind is compiled with true or false, the emitted override carries a runtime guard: Application.get_env(:bond, <kind>, <compile_time_value>). The contract is evaluated unless the runtime value is exactly false. Operators can flip contracts on or off via Application.put_env/3 from a remote console — no recompilation needed. The compile-time value sets the default for the runtime guard.

    Benchmark on the project fixture (bench/runtime_check_overhead.exs, trivial @pre is_number(x) in a tight loop): :purge ~48 ns/call, false ~89 ns/call (~40 ns guard overhead), true ~155 ns/call (guard plus assertion eval).

  • :overrides config for per-module rules. A list of {Module | Regex, opts} tuples. Module-atom keys match exactly; Regex keys match against the source-visible module name (no Elixir. prefix). Use this to opt specific modules in or out of contract compilation without touching their source. Example:

    config :bond,
  preconditions: true,
  overrides: [
    {MyApp.HotPath, preconditions: :purge, postconditions: :purge},
    {~r/Workers\\./, postconditions: false}
  ]

  • use Bond, opts per-module options. Pass any of :preconditions, :postconditions, :checks directly at the use site to override global and :overrides settings for that module.

    defmodule MyApp.HotPath do
  use Bond, preconditions: :purge, postconditions: :purge
end

    Precedence: use Bond opts > exact-atom :overrides match > first Regex :overrides match > global config.

  • Bond.Compiler.resolve_config/3 — internal helper exposed for testing that combines global config, :overrides, and use Bond opts into the final per-module mode map.

Changed

  • Bond.Compiler.AnnotatedFunction.apply_contract/2 now expects each kind in the config map to be true | false | :purge rather than a boolean. The function returns nil when both kinds resolve to :purge; in all other cases it emits the override with the appropriate runtime guards.

  • Bond.check/1,2 now expands to a runtime-guarded call when the resolved :checks mode is true or false, and to :ok (a compile-time no-op) when the mode is :purge.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.10.0] - 2026-05-21

The headline feature of 0.10.0 is conditional compilation of contracts. You can now compile some or all of your contracts out entirely via application config, with zero per-call overhead for disabled contracts. The release also adds an ExUnit helper module, polishes error reporting, and substantially rewrites the user-facing documentation.

Added

  • Conditional compilation via :bond application config. Three keys, read at compile time via Application.compile_env/3:

    • :preconditions (default true) — when false, no precondition evaluation is emitted in override clauses, and the auto-generated #### Preconditions doc section is omitted.
    • :postconditions (default true) — same for postconditions.
    • :checks (default true) — when false, every check/1,2 macro call in modules that use Bond expands to :ok and the wrapped expression is not evaluated. (Don't put side effects inside check.)

    When both :preconditions and :postconditions are disabled for a function, Bond emits no override at all. The function runs exactly as written, with zero per-call overhead. The function's auto-generated contract docs are also suppressed in that case.

    See the new "Conditional compilation" section in the Bond moduledoc.

  • Bond.Test module with assert_precondition_violation/2, assert_postcondition_violation/2, and assert_check_violation/2 macros for testing contract violations in ExUnit. Field expectations (:label, :expression, etc.) can be exact values or Regex patterns.

  • New guides/faq.md answering the questions that come up most: why contracts when I have ExUnit, will contracts slow down prod, how does Bond compare to Norm, what does Bond do that typespecs don't, the Assertion Evaluation rule, default-arg behaviour, multi-clause handling.

Changed

  • Assertion failure messages pretty-print the captured binding/0 with inspect/2 ... pretty: true, limit: 20, printable_limit: 200, width: 80, so small bindings stay compact and large structs no longer dominate the failure output.

  • Stack traces of raised assertion exceptions are pruned to omit Bond.* frames. Failures point at the user's call site rather than into Bond.Runtime.Eval.

  • Bond moduledoc / README restructured. Leads with a five-line Account.withdraw example and a one-paragraph elevator pitch. The Wikipedia quote moves out. Assertion syntax recommends the keyword-list form as primary. New Conditional compilation section. The Math.sqrt example remains as the "showing everything" sample.

  • guides/getting-started.md expanded into a step-by-step walkthrough: first @pre, postcondition with result, labelled assertions, predicates, old expressions, inline checks, disabling in prod, and ExUnit integration.

Internal

  • New private function in Bond.Runtime.Eval that prunes Bond frames from the captured stack trace before raising.
  • Bond.Compiler.AnnotatedFunction.apply_contract/1 is now apply_contract/2 taking a contract_config map. The __before_compile__/1 callback reads the config from a @__bond_contract_config__ module attribute set by Bond's __using__/1.

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.9.1] - 2026-05-21

A patch release covering documentation cleanup left over from the 0.9.0 refactor plus a handful of usability improvements.

Added

  • .formatter.exs is now published with the Hex package and declares locals_without_parens for check/1, check/2, and old/1. Downstream projects can pick these up with import_deps: [:bond] in their own .formatter.exs.
  • Assertion-failure messages now include an at: <file>:<line> line so the source location is clickable in editors.

Changed

  • binding/0 captured in assertion-failure info is sorted by name so failure messages are reproducible across runs.

Fixed

  • README/moduledoc no longer references the removed Bond.def/2 and Bond.defp/2 macros, eliminating mix docs cross-reference warnings.
  • The getting-started guide installation hint now references the current version.
  • CHANGELOG no longer auto-links the removed define_function_with_contract/4 helper.

Internal

[0.9.0] - 2026-05-21

This release is a large internal refactor with no breaking changes to the public API. @pre, @post, and check/1,2 all behave the same as in 0.8.x.

Changed

  • Bond no longer overrides Kernel.def/2 and Kernel.defp/2. Contracts are now applied via Elixir compiler hooks (@on_definition, @before_compile, @after_compile). This makes Bond more robust against changes in Elixir's macro expansion semantics, eliminates a class of macro-hygiene issues, and plays nicer with other macros that produce function definitions.
  • Multi-clause functions are now wrapped by a single override clause that delegates to super/1 rather than having contract logic inlined into each clause. Elixir's normal pattern matching handles dispatch inside the super call.
  • Assertion failures are signalled by a throw / catch instead of being raised inline. Each @pre/@post group compiles to an anonymous function that throws {:assertion_failure, info} on the first failure; Bond.Runtime.Eval catches it and raises the appropriate exception type.
  • Functions with contracts now get auto-generated Preconditions and Postconditions sections in their documentation even if the user did not attach a @doc themselves. Previously contract documentation was only emitted when a @doc was present.
  • Internal modules are reorganised into Bond.Compiler.* (compile-time) and Bond.Runtime.* (run-time) namespaces.

Internal

Requirements

  • Unchanged. Elixir ~> 1.14.

[0.8.3] - 2024-11-08

Released before this changelog was established. See the git history for details.