[clang] [clang][analyzer] Support `fgetc` in StreamChecker (PR #72627)

[Balázs Kéri via cfe-commits]

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@@ -101,6 +101,30 @@ void error_fwrite(void) {
   Ret = fwrite(0, 1, 10, F); // expected-warning {{Stream might be already closed}}
 }
 
+void error_fgetc(void) {
+  FILE *F = tmpfile();
+  if (!F)
+    return;
+  int Ret = fgetc(F);
+  if (0 <= Ret && Ret <= 255) {
+    clang_analyzer_eval(feof(F) || ferror(F)); // expected-warning {{FALSE}}
+  } else {
+    clang_analyzer_eval(Ret == EOF);  // expected-warning {{TRUE}}
+    if (feof(F)) {
+      clang_analyzer_warnIfReached(); // expected-warning {{REACHABLE}}
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balazske wrote:

These `warnIfReached` calls are not necessary, because the presence of the next warning tells anyway that the code is reachable.

https://github.com/llvm/llvm-project/pull/72627