[clang] [clang][analyzer] Improve documentation of StreamChecker (NFC). (PR #83858)

[Balázs Kéri via cfe-commits]

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@@ -3020,44 +3020,82 @@ Check for misuses of stream APIs. Check for misuses of stream APIs: ``fopen, fcl
 
 alpha.unix.Stream (C)
 """""""""""""""""""""
-Check stream handling functions: ``fopen, tmpfile, fclose, fread, fwrite, fseek, ftell, rewind, fgetpos,``
-``fsetpos, clearerr, feof, ferror, fileno``.
+Check C stream handling functions:
+``fopen, fdopen, freopen, tmpfile, fclose, fread, fwrite, fgetc, fgets, fputc, fputs, fprintf, fscanf, ungetc, getdelim, getline, fseek, fseeko, ftell, ftello, fflush, rewind, fgetpos, fsetpos, clearerr, feof, ferror, fileno``.
+
+The checker maintains information about the C stream objects (``FILE *``) and
+can detect error conditions related to use of streams. The following conditions
+are detected:
+
+* The ``FILE *`` pointer passed to the function is NULL (the single exception is
+  ``fflush`` where NULL is allowed).
+* Use of stream after close.
+* Opened stream is not closed.
+* Read from a stream after end-of-file. (This is not a fatal error but reported
+  by the checker. Stream remains in EOF state and the read operation fails.)
----------------
balazske wrote:

I have the feeling that these words (NULL, EOF) are relatively commonly used (NULL is an abbrevation for null pointer, EOF = end-of-file). Probably `NULL` can be better as keyword (code format), but by EOF I did not mean the numeric constant, just "end of file".

https://github.com/llvm/llvm-project/pull/83858