Pentiment

Beautiful, compiler-style diagnostic messages for Elixir.

State machine error example

Features

Rich source context — Highlighted code spans with line numbers and visual pointers
Syntax highlighting — Source excerpts colorized via optional makeup lexers
Multiple labels — Primary and secondary annotations to show related code locations
Helpful metadata — Error codes, notes, and actionable suggestions
Flexible spans — Line/column positions, byte offsets, or deferred pattern search
Elixir integration — Extract spans directly from AST metadata

Installation

def deps do
  [{:pentiment, "~> 0.2"}]
end

Quick Example

alias Pentiment.{Report, Label, Span, Source}

report =
  Report.error("Undefined variable")
  |> Report.with_code("E001")
  |> Report.with_source("lib/app.ex")
  |> Report.with_label(Label.primary(Span.position(10, 5), "not found in scope"))
  |> Report.with_help("did you mean `user`?")

source = Source.from_file("lib/app.ex")
IO.puts(Pentiment.format(report, source))

Syntax Highlighting

Pentiment has no hard runtime dependencies. To syntax-highlight the source excerpts in rendered diagnostics, add the makeup lexers for the languages you report on:

def deps do
  [
    {:pentiment, "~> 0.2"},
    {:makeup_elixir, "~> 1.0"},
    {:makeup_erlang, "~> 1.0"}
  ]
end

Highlighting activates automatically (syntax: :auto) when ANSI colors are active, a lexer is available, and the source's language is known — inferred from the source name's extension (.ex/.exs, .erl/.hrl), or set explicitly with Pentiment.Source.from_string("gen.ex", code, language: :elixir). Pass syntax: false to disable it, or colors: false for fully plain output (for example, when rendering into editor diagnostics). A custom highlighter module implementing Pentiment.Highlighter can be supplied via the :highlighter option.

Use Cases

Pentiment is designed for:

Compile-time macro errors — Validate DSL usage with precise source locations
Parser error reporting — Convert parse failures into helpful diagnostics
Configuration validation — Catch invalid keys and suggest corrections
Custom linters — Build tools that report issues with rich context

Documentation

Examples Overview — Integration patterns and quick start
Config Validation — Compile-time config checking
State Machine DSL — Multi-span errors
Guard Restriction — AST walking patterns
Parser Errors — NimbleParsec integration
YAML Validation — Semantic file validation

Full API documentation available on HexDocs.

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