[clang] [clang][analyzer] Improve modeling of 'realpath' in StdLibraryFunctionsChecker (PR #79939)

[Balázs Kéri via cfe-commits]

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@@ -2992,12 +2992,14 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
 
     // char *realpath(const char *restrict file_name,
     //                char *restrict resolved_name);
-    // FIXME: Improve for errno modeling.
     addToFunctionSummaryMap(
         "realpath",
         Signature(ArgTypes{ConstCharPtrRestrictTy, CharPtrRestrictTy},
                   RetType{CharPtrTy}),
-        Summary(NoEvalCall).ArgConstraint(NotNull(ArgNo(0))));
+        Summary(NoEvalCall)
+            .Case({NotNull(Ret)}, ErrnoMustNotBeChecked, GenericSuccessMsg)
+            .Case({IsNull(Ret)}, ErrnoNEZeroIrrelevant, GenericFailureMsg)
+            .ArgConstraint(NotNull(ArgNo(0))));
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balazske wrote:

The buffer at arg 1 should have size of `MAX_PATH` if not null, this can be additional improvement (probably add a FIXME for it).

https://github.com/llvm/llvm-project/pull/79939