[clang] Fix FP -Wformat in functions with 2+ attribute((format))

When defining functions with two or more format attributes, if the
format strings don't have the same format family, there is a false
positive warning that the incorrect kind of format string is being
passed at forwarded format string call sites.

Author: apple-fcloutier

clang/lib/Sema/SemaChecking.cpp

@@ -6149,18 +6149,19 @@ static StringLiteralCheckType checkFormatStringExpr(
             if (!Sema::getFormatStringInfo(D, PVFormat->getFormatIdx(),
                                            PVFormat->getFirstArg(), &CallerFSI))
               continue;
-            // We also check if the formats are compatible.
-            // We can't pass a 'scanf' string to a 'printf' function.
-            if (Type != S.GetFormatStringType(PVFormat)) {
-              S.Diag(Args[format_idx]->getBeginLoc(),
-                     diag::warn_format_string_type_incompatible)
-                  << PVFormat->getType()->getName()
-                  << S.GetFormatStringTypeName(Type);
-              if (!InFunctionCall) {
-                S.Diag(E->getBeginLoc(), diag::note_format_string_defined);
+            if (PV->getFunctionScopeIndex() == CallerFSI.FormatIdx) {
+              // We also check if the formats are compatible.
+              // We can't pass a 'scanf' string to a 'printf' function.
+              if (Type != S.GetFormatStringType(PVFormat)) {
+                S.Diag(Args[format_idx]->getBeginLoc(),
+                       diag::warn_format_string_type_incompatible)
+                    << PVFormat->getType()->getName()
+                    << S.GetFormatStringTypeName(Type);
+                if (!InFunctionCall) {
+                  S.Diag(E->getBeginLoc(), diag::note_format_string_defined);
+                }
+                return SLCT_UncheckedLiteral;
               }
-              return SLCT_UncheckedLiteral;
-            } else if (PV->getFunctionScopeIndex() == CallerFSI.FormatIdx) {
               // Lastly, check that argument passing kinds transition in a
               // way that makes sense:
               // from a caller with FAPK_VAList, allow FAPK_VAList

clang/test/Sema/format-strings.c

@@ -496,6 +496,26 @@ void rdar8332221(va_list ap, int *x, long *y) {
   rdar8332221_vprintf_scanf("%", ap, "%d", x); // expected-warning{{incomplete format specifier}}
 }
 
+void rdar8332221_vprintf_scanf(const char *p, va_list ap, const char *s, ...) {
+  vprintf(p, ap);
+
+  va_list vs;
+  va_start(vs, s);
+  vscanf(s, vs);
+  va_end(vs);
+}
+
+__attribute__((__format__(__printf__, 1, 0)))
+__attribute__((__format__(__scanf__, 3, 4)))
+void vprintf_scanf_bad(const char *p, va_list ap, const char *s, ...) {
+  vscanf(p, ap); // expected-warning{{passing 'printf' format string where 'scanf' format string is expected}}
+
+  va_list vs;
+  va_start(vs, s);
+  vprintf(s, vs); // expected-warning{{passing 'scanf' format string where 'printf' format string is expected}}
+  va_end(vs);
+}
+
 // PR8641
 void pr8641(void) {
   printf("%#x\n", 10);