I append new_text as a new function just before module's closing end, located from the parse so a sibling or nested module in the same file doesn't misdirect it. Returns source unchanged when module has no defmodule to append to (e.g. a typedstruct-generated module), or the source doesn't parse.

I return the alias/import/require statements ast declares — whole statements, so formatter-wrapped directives arrive intact. With no module I sweep the top level and every top-level module (buffer semantics); given a dotted module name I scope to that module's own body, so siblings in the same file don't leak theirs in.

I parse source and return the AST function entries (the same shape all_functions/1 returns minus the runtime-export merging, which needs the module to be loaded). Works on disk bytes alone, so safe to call before / after a failed compile.

I extract the top-level defmodule X.Y name from source. Returns the dotted module string, or nil when the source doesn't define one or doesn't parse.

I return every module source defines (nested defmodules and typedstruct module: children included) as dotted-name strings. Returns [] when the source doesn't parse.

I parse source with the options every source walk uses.

I replace the {name, arity} function within module in source with new_text (or remove it when new_text is empty), taking the range from source itself so the splice can't drift. Unknown name/arity returns source unchanged.

I swap two functions (by {name, arity}) within module in source, taking ranges from source itself so the splice can't drift. Unknown name/arity returns source unchanged.