[clang] [clang][analyzer] Support `fputc` in StreamChecker (PR #71518)

[Balázs Kéri via cfe-commits]

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@@ -268,3 +302,20 @@ void error_indeterminate_feof2(void) {
   }
   fclose(F);
 }
+
+void error_indeterminate_feof3(void) {
+  FILE *F = fopen("file", "r+");
+  if (!F)
+    return;
+  char Buf[10];
+  if (fread(Buf, 1, 10, F) < 10) {
+    if (feof(F)) {
+      // error is feof, should be non-indeterminate
+      fputc(';', F); // no warning
+    }
+    if (ferror(F)) {
+      fputc('=', F); // expected-warning {{might be 'indeterminate'}}
+    }
+  }
+  fclose(F);
+}
----------------
balazske wrote:

I think that these 2 added "indeterminate" tests should be combined into one, or this last can be removed. The tests called `error_indeterminate_eof` have the role to test when the stream becomes indeterminate (or not) and use the function `fwrite` only to check for the presence of indeterminate state, not to test `fwrite` itself. So it is not necessary to repeat similar tests with `fputc`. But a test is needed to check if a warning for indeterminate state is produced by `fputc` in the correct cases, and no warnings for EOF, the function `error_indeterminate_fputc` does this already.

It would be better if there would be new debug functions in the checker that can get if the stream is "indeterminate" and one that can be used to set values of indeterminate, ferror, feof in a stream. Then the tests can be simplified. But this is only an idea for another PR, probably I will do this later.

https://github.com/llvm/llvm-project/pull/71518