Two rules the AST makes possible, plus the mutation analysis behind them.
const-local reports a local that is never written. It is restricted to SCALARS
— integers, bools, enums, floating types — and that restriction is what makes
the answer exact rather than a guess: a scalar has no member functions, so the
only ways to write one are assignment, ++/--, having its address taken, or
binding to a non-const reference. All four are now tracked in the walk:
- assignment and compound assignment visit their LEFT operand in a write
context, the right one normally;
- ++/-- and & write their operand;
- a call argument is checked against the callee's parameter type, so passing
to `const int&` or by value is a read while `int&` is a write;
- initialising a non-const reference writes what it binds to.
For a class type a non-const method call could mutate it, and deciding that is
the whole-program analysis clang-tidy does, so those are simply out of scope
rather than guessed at.
constexpr-constant promotes a const constant whose initialiser is made only of
literals and operators, so `const int A = 1 << 4;` qualifies and
`const int B = Compute();` does not.
On this repository const-local found 103 candidates, which was too many to be
useful, and the reason was informative: most were range-for bindings and
pointer locals. `for (T* const x : …)` and `T* const p` are not spellings
anybody writes, and the useful constness for a pointer is on the pointee, which
this rule cannot advise on. Excluding both leaves 36, all plain bool or enum
locals worth fixing — isWasm, isPe, exists, writes, isC and so on. Those 36 are
fixed in this commit; the compiler verified every one.
Both rules are report-only. The analysis is exact, but adding const is a
judgement about intent as much as mechanics, and a wrong suggestion should cost
a glance rather than a build. const-local also deliberately does not become a
transform: inserting `const` before a shared type would apply it to every
declarator in a multi-declarator statement, including any that IS written.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
The rule was 125 lines: four std::regex, a hand-rolled {/} scope stack, a
cumulative paren-depth counter so a wrapped parameter list would not look like
a declaration, a 40-entry keyword denylist, and a "function-shaped line" guess
whose own comment conceded it was heuristic. Storage class came from
lineStr.contains("static "). It is now ~55 lines that ask clang what kind of
declaration each thing is and what encloses it.
The three regressions the old version carried special cases for — a call with
an inline lambda argument, a bare statement call, a one-liner method — need no
handling at all, because a call is not a declaration. Their tests pass
unchanged.
On this repository the exact version found 42 violations the heuristic had
never been able to see, all real:
- 37 members of the libclang function-pointer table added two commits ago
were PascalCase. The old varDecl regex could not match a declaration whose
type is decltype(&f), so they were silently skipped. Renamed to camelCase,
which mirrors clang_createIndex -> createIndex more closely anyway.
- Crafter.Build-Shader.cpp had a snake_case local, file_name_list, invisible
to the heuristic for the same reason (it declares a const char* array).
- Four extern "C" declarations of libc functions in tests were reported as
badly-named functions. Those are named by the C library, so C language
linkage is now an exemption — the same principled test no-char-pointer
uses, rather than another denylist entry.
New tests cover what the line-based version structurally could not reach: a
signature wrapped over several lines, `static` on its own line above the
declaration it applies to, and a member versus a local inside a method.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Canonical LGPL-3.0-only text, GPL-3.0 companion, SPDX headers on all
first-party sources, MIT for examples/. Vendored lib/ untouched.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
