[clang] [clang][analyzer] Add missing stream related functions to StdLibraryFunctionsChecker. (PR #76979)

[Balázs Kéri via cfe-commits]

================
@@ -2201,6 +2214,56 @@ void StdLibraryFunctionsChecker::initFunctionSummaries(
                   ErrnoNEZeroIrrelevant, GenericFailureMsg)
             .ArgConstraint(NotNull(ArgNo(0))));
 
+    // int fgetc(FILE *stream);
+    // 'getc' is the same as 'fgetc' but may be a macro
+    addToFunctionSummaryMap(
+        {"getc", "fgetc"}, Signature(ArgTypes{FilePtrTy}, RetType{IntTy}),
+        Summary(NoEvalCall)
+            .Case({ReturnValueCondition(WithinRange, {{0, UCharRangeMax}})},
+                  ErrnoMustNotBeChecked, GenericSuccessMsg)
+            .Case({ReturnValueCondition(WithinRange, SingleValue(EOFv))},
+                  ErrnoNEZeroIrrelevant, GenericFailureMsg)
+            .ArgConstraint(NotNull(ArgNo(0))));
----------------
balazske wrote:

In this case `ErrnoNEZeroIrrelevant` can not be used because we do not know what will happen with `errno`. The situation can be improved if `StreamChecker` sets the state of `errno`, but this would be a large change.

https://github.com/llvm/llvm-project/pull/76979