fixup! fixup! fixup! fixup! fixup! fixup! fixup! Fix #1473: warn when fclose() is used as a while loop condition

Author: francois-berder

man/checkers/fcloseInLoopCondition.md

@@ -0,0 +1,40 @@
+# fcloseInLoopCondition
+
+**Message**: fclose() used as loop condition may skip loop body or double-close file handle.<br/>
+**Category**: Resource Management<br/>
+**Severity**: Warning<br/>
+**Language**: C and C++
+
+## Description
+
+Using `fclose()` as a loop condition leads to two unwanted outcomes:
+
+- On **success**, the condition is false and the loop body never executes. The intent was likely to process the file inside the loop, but it is already closed.
+- On **failure**, the condition is true and the loop body executes but `fclose()` is called again on the already-closed file handle on the next iteration, which is undefined behaviour.
+
+This pattern is almost always a misunderstanding of what `fclose()` returns, or confusion with a function that reads/processes data incrementally (like `fgets` or `fread`). Unlike those functions, `fclose()` is a one-shot teardown operation and has no meaningful retry or loop-until-done semantic.
+
+## How to fix
+
+Call `fclose()` outside the loop condition. If you need to check whether the close succeeded, store the return value and test it separately.
+
+Before:
+```c
+FILE *fp = fopen("data.txt", "r");
+while (fclose(fp)) {
+    /* process file */
+}
+```
+
+After:
+```c
+FILE *fp = fopen("data.txt", "r");
+/* process file */
+if (fclose(fp) != 0) {
+    /* handle close error */
+}
+```
+
+## Related checkers
+
+- `useClosedFile` - for using a file handle that has already been closed