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

Using fclose() as a while loop condition closes the file on every
iteration and operates on an already-closed file handle from the
second iteration onward.

Signed-off-by: Francois Berder <fberder@outlook.fr>

Author: francois-berder

lib/checkio.cpp

@@ -245,6 +245,19 @@ void CheckIO::checkFileUsage()
                 } else if (tok->str() == "fclose") {
                     fileTok = tok->tokAt(2);
                     operation = Filepointer::Operation::CLOSE;
+
+                    // #1473 Check if fclose is in a while loop condition
+                    const Token* tmp = tok->astParent();
+                    const Token* loopTok = nullptr;
+                    while (tmp) {
+                        if (Token::simpleMatch(tmp->previous(), "while (")) {
+                            loopTok = tmp->previous();
+                            break;
+                        }
+                        tmp = tmp->astParent();
+                    }
+                    if (loopTok)
+                        useClosedFileError(tok);
                 } else if (whitelist.find(tok->str()) != whitelist.end()) {
                     fileTok = tok->tokAt(2);
                     if ((tok->str() == "ungetc" || tok->str() == "ungetwc") && fileTok)

test/testio.cpp

@@ -544,7 +544,7 @@ class TestIO : public TestFixture {
               "    FILE *a = fopen(\"aa\", \"r\");\n"
               "    while (fclose(a)) {}\n"
               "}");
-        TODO_ASSERT_EQUALS("[test.cpp:3:5]: (error) Used file that is not opened. [useClosedFile]\n", "", errout_str());
+        ASSERT_EQUALS("[test.cpp:3:12]: (error) Used file that is not opened. [useClosedFile]\n", errout_str());
 
         // #6823
         check("void foo() {\n"