[clang] [clang][doc] Provide documentation for FixedPointLiteral matcher (PR #125122)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: None (earnol)

<details>
<summary>Changes</summary>

Provide a documentation for FixedPointLiteral exaplaining which literals will be matched and which are not. This documentation is compatible with https://github.com/llvm/llvm-project/commit/53e92e48d0c03a2475e8517dd4c28968d84fc217 change.

---
Full diff: https://github.com/llvm/llvm-project/pull/125122.diff


1 Files Affected:

- (modified) clang/include/clang/ASTMatchers/ASTMatchers.h (+22-1) 


``````````diff
diff --git a/clang/include/clang/ASTMatchers/ASTMatchers.h b/clang/include/clang/ASTMatchers/ASTMatchers.h
index 239fcba4e5e057..0f7e3a8a01762c 100644
--- a/clang/include/clang/ASTMatchers/ASTMatchers.h
+++ b/clang/include/clang/ASTMatchers/ASTMatchers.h
@@ -2489,7 +2489,28 @@ extern const internal::VariadicDynCastAllOfMatcher<Stmt, FloatingLiteral>
 extern const internal::VariadicDynCastAllOfMatcher<Stmt, ImaginaryLiteral>
     imaginaryLiteral;
 
-/// Matches fixed point literals
+/// Matches fixed-point literals eg.
+/// 0.5r, 0.5hr, 0.5lr, 0.5uhr, 0.5ur, 0.5ulr
+/// 1.0k, 1.0hk, 1.0lk, 1.0uhk, 1.0uk, 1.0ulk
+/// Exponents 1.0e10k
+/// Hexadecimal numbers 0x0.2p2r
+///
+/// Does not match implicit conversions such as first two lines:
+/// \code
+///    short _Accum sa = 2;
+///    _Accum a = 12.5;
+///    _Accum b = 1.25hk;
+///    _Fract c = 0.25hr;
+///    _Fract v = 0.35uhr;
+///    _Accum g = 1.45uhk;
+///    _Accum decexp1 = 1.575e1k;
+/// \endcode
+/// \compile_args{-ffixed-point;-std=c99}
+///
+/// The matcher \matcher{fixedPointLiteral()} matches
+/// \match{1.25hk}, \match{0.25hr}, \match{0.35uhr},
+/// \match{1.45uhk}, \match{1.575e1k}, but does not
+/// match \nomatch{12.5} and \nomatch{2} from the code block.
 extern const internal::VariadicDynCastAllOfMatcher<Stmt, FixedPointLiteral>
     fixedPointLiteral;
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/125122