[clang] [Sema] Fix missing warnings for unused args with invalid printf specs. (PR #158514)

via cfe-commits cfe-commits at lists.llvm.org
Sun Sep 14 14:53:47 PDT 2025 

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Lakreite (lakreite)

<details>
<summary>Changes</summary>

Before this change, the analyzer didn't emit warnings for unused arguments when the format string contained invalid `printf` specifier (printf, os_log, NSLog) at the end of the format string.
Before:
```c
    printf("%1", 123); // incomplete format specifier
    printf("%d %d %d %1", 123, 123, 123, 123); // incomplete format specifier
    printf("%1 %d", 123, 123); // incomplete format specifier | data argument not used by format string
```
After:
```c
  printf("%1", 123); // incomplete format specifier | data argument not used by format string
  printf("%d %d %d %1", 123, 123, 123, 123); // incomplete format specifier | data argument not used by format string
```
Added new test cases in:
- clang/test/Sema/format-strings.c
- clang/test/SemaObjC/format-strings-objc.m
- clang/test/SemaOpenCL/printf-format-strings.cl

---
Full diff: https://github.com/llvm/llvm-project/pull/158514.diff


4 Files Affected:

- (modified) clang/lib/AST/PrintfFormatString.cpp (+1-1) 
- (modified) clang/test/Sema/format-strings.c (+14-14) 
- (modified) clang/test/SemaObjC/format-strings-objc.m (+5-5) 
- (modified) clang/test/SemaOpenCL/printf-format-strings.cl (+6-6) 


``````````diff
diff --git a/clang/lib/AST/PrintfFormatString.cpp b/clang/lib/AST/PrintfFormatString.cpp
index 855550475721a..f829696a26473 100644
--- a/clang/lib/AST/PrintfFormatString.cpp
+++ b/clang/lib/AST/PrintfFormatString.cpp
@@ -440,7 +440,7 @@ bool clang::analyze_format_string::ParsePrintfString(FormatStringHandler &H,
     // Did a fail-stop error of any kind occur when parsing the specifier?
     // If so, don't do any more processing.
     if (FSR.shouldStop())
-      return true;
+      return false;
     // Did we exhaust the string or encounter an error that
     // we can recover from?
     if (!FSR.hasValue())
diff --git a/clang/test/Sema/format-strings.c b/clang/test/Sema/format-strings.c
index af30ad5d15fe2..e2f03089c12be 100644
--- a/clang/test/Sema/format-strings.c
+++ b/clang/test/Sema/format-strings.c
@@ -207,9 +207,9 @@ void check_invalid_specifier(FILE* fp, char *buf)
 
 void check_null_char_string(char* b)
 {
-  printf("\0this is bogus%d",1); // expected-warning {{string contains '\0'}}
-  snprintf(b,10,"%%%%%d\0%d",1,2); // expected-warning {{string contains '\0'}}
-  printf("%\0d",1); // expected-warning {{string contains '\0'}}
+  printf("\0this is bogus%d",1); // expected-warning {{string contains '\0'}} expected-warning {{data argument not used by format string}}
+  snprintf(b,10,"%%%%%d\0%d",1,2); // expected-warning {{string contains '\0'}} expected-warning {{data argument not used by format string}}
+  printf("%\0d",1); // expected-warning {{string contains '\0'}} expected-warning {{data argument not used by format string}}
 }
 
 void check_empty_format_string(char* buf, ...)
@@ -297,7 +297,7 @@ void test10(int x, float f, int i, long long lli) {
   printf("%W%d\n", x, x); // expected-warning{{invalid conversion specifier 'W'}}  expected-warning {{data argument not used by format string}}
   printf("%"); // expected-warning{{incomplete format specifier}}
   printf("%.d", x); // no-warning
-  printf("%.", x);  // expected-warning{{incomplete format specifier}}
+  printf("%.", x);  // expected-warning{{incomplete format specifier}} expected-warning {{data argument not used by format string}}
   printf("%f", 4); // expected-warning{{format specifies type 'double' but the argument has type 'int'}}
   printf("%qd", lli); // no-warning
   printf("%qd", x); // expected-warning{{format specifies type 'long long' but the argument has type 'int'}}
@@ -390,8 +390,8 @@ void test_unicode_conversions(wchar_t *s) {
 // This is an IEEE extension (IEEE Std 1003.1).
 // FIXME: This is probably not portable everywhere.
 void test_positional_arguments(void) {
-  printf("%0$", (int)2); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}}
-  printf("%1$*0$d", (int) 2); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}}
+  printf("%0$", (int)2); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}} expected-warning{{data argument not used by format string}}
+  printf("%1$*0$d", (int) 2); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}} expected-warning{{data argument not used by format string}}
   printf("%1$d", (int) 2); // no-warning
   printf("%1$d", (int) 2, 2); // expected-warning{{data argument not used by format string}}
   printf("%1$d%1$f", (int) 2); // expected-warning{{format specifies type 'double' but the argument has type 'int'}}
@@ -595,16 +595,16 @@ void pr9751(void) {
   printf("%y", 5); // expected-warning{{invalid conversion specifier 'y'}}
 
   const char kFormat5[] = "%."; // expected-note{{format string is defined here}}
-  printf(kFormat5, 5); // expected-warning{{incomplete format specifier}}
-  printf("%.", 5); // expected-warning{{incomplete format specifier}}
+  printf(kFormat5, 5); // expected-warning{{incomplete format specifier}} expected-warning{{data argument not used by format string}}
+  printf("%.", 5); // expected-warning{{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 
   const char kFormat6[] = "%s"; // expected-note{{format string is defined here}}
   printf(kFormat6, 5); // expected-warning{{format specifies type 'char *' but the argument has type 'int'}}
   printf("%s", 5); // expected-warning{{format specifies type 'char *' but the argument has type 'int'}}
 
   const char kFormat7[] = "%0$"; // expected-note{{format string is defined here}}
-  printf(kFormat7, 5); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}}
-  printf("%0$", 5); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}}
+  printf(kFormat7, 5); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}} expected-warning{{data argument not used by format string}}
+  printf("%0$", 5); // expected-warning{{position arguments in format strings start counting at 1 (not 0)}} expected-warning{{data argument not used by format string}}
 
   const char kFormat8[] = "%1$d %d"; // expected-note{{format string is defined here}}
   printf(kFormat8, 4, 4); // expected-warning{{cannot mix positional and non-positional arguments in format string}}
@@ -615,8 +615,8 @@ void pr9751(void) {
   printf("", 4, 4); // expected-warning{{format string is empty}}
 
   const char kFormat10[] = "\0%d"; // expected-note{{format string is defined here}}
-  printf(kFormat10, 4); // expected-warning{{format string contains '\0' within the string body}}
-  printf("\0%d", 4); // expected-warning{{format string contains '\0' within the string body}}
+  printf(kFormat10, 4); // expected-warning{{format string contains '\0' within the string body}} expected-warning{{data argument not used by format string}}
+  printf("\0%d", 4); // expected-warning{{format string contains '\0' within the string body}} expected-warning{{data argument not used by format string}}
 
   const char kFormat11[] = "%*d"; // expected-note{{format string is defined here}}
   printf(kFormat11); // expected-warning{{'*' specified field width is missing a matching 'int' argument}}
@@ -720,8 +720,8 @@ extern void test14_bar(const char *, const char *, ...)
      __attribute__((__format__(__printf__, 1, 3)));
 
 void test14_zed(int *p) {
-  test14_foo("%", "%d", p); // expected-warning{{incomplete format specifier}}
-  test14_bar("%", "%d", p); // expected-warning{{incomplete format specifier}}
+  test14_foo("%", "%d", p); // expected-warning{{incomplete format specifier}} expected-warning{{data argument not used by format string}}
+  test14_bar("%", "%d", p); // expected-warning{{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 }
 
 #if !defined(__ANDROID__) && !defined(__Fuchsia__)
diff --git a/clang/test/SemaObjC/format-strings-objc.m b/clang/test/SemaObjC/format-strings-objc.m
index 40c1d31b1fd4c..aba1f6153a9a4 100644
--- a/clang/test/SemaObjC/format-strings-objc.m
+++ b/clang/test/SemaObjC/format-strings-objc.m
@@ -274,15 +274,15 @@ void testUnicode(void) {
 
 // Test Objective-C modifier flags.
 void testObjCModifierFlags(void) {
-  NSLog(@"%[]@", @"Foo"); // expected-warning {{missing object format flag}}
-  NSLog(@"%[", @"Foo"); // expected-warning {{incomplete format specifier}}
-  NSLog(@"%[tt", @"Foo");  // expected-warning {{incomplete format specifier}}
+  NSLog(@"%[]@", @"Foo"); // expected-warning {{missing object format flag}} expected-warning{{data argument not used by format string}}
+  NSLog(@"%[", @"Foo"); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
+  NSLog(@"%[tt", @"Foo");  // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
   NSLog(@"%[tt]@", @"Foo"); // no-warning
   NSLog(@"%[tt]@ %s", @"Foo", "hello"); // no-warning
   NSLog(@"%s %[tt]@", "hello", @"Foo"); // no-warning
-  NSLog(@"%[blark]@", @"Foo"); // expected-warning {{'blark' is not a valid object format flag}}
+  NSLog(@"%[blark]@", @"Foo"); // expected-warning {{'blark' is not a valid object format flag}} expected-warning{{data argument not used by format string}}
   NSLog(@"%2$[tt]@ %1$[tt]@", @"Foo", @"Bar"); // no-warning
-  NSLog(@"%2$[tt]@ %1$[tt]s", @"Foo", @"Bar"); // expected-warning {{object format flags cannot be used with 's' conversion specifier}}
+  NSLog(@"%2$[tt]@ %1$[tt]s", @"Foo", @"Bar"); // expected-warning {{object format flags cannot be used with 's' conversion specifier}} expected-warning{{data argument not used by format string}}
 }
 
 @interface RD23622446_Tester: NSObject
diff --git a/clang/test/SemaOpenCL/printf-format-strings.cl b/clang/test/SemaOpenCL/printf-format-strings.cl
index 6cdfc7e60b379..e5b1e5a914290 100644
--- a/clang/test/SemaOpenCL/printf-format-strings.cl
+++ b/clang/test/SemaOpenCL/printf-format-strings.cl
@@ -96,18 +96,18 @@ kernel void format_v4f32(float4 arg)
 
 kernel void format_only_v(int arg)
 {
-    printf("%v", arg); // expected-warning {{incomplete format specifier}}
+    printf("%v", arg); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 }
 
 kernel void format_missing_num(int arg)
 {
-    printf("%v4", arg); // expected-warning {{incomplete format specifier}}
+    printf("%v4", arg); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 }
 
 kernel void format_not_num(int arg)
 {
-    printf("%vNd", arg); // expected-warning {{incomplete format specifier}}
-    printf("%v*d", arg); // expected-warning {{incomplete format specifier}}
+    printf("%vNd", arg); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
+    printf("%v*d", arg); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 }
 
 kernel void format_v16i32(int16 arg)
@@ -127,7 +127,7 @@ kernel void format_v4i32_wrong_num_elts_2_to_4(int2 arg)
 
 kernel void format_missing_num_elts_format(int4 arg)
 {
-    printf("%vd\n", arg); // expected-warning {{incomplete format specifier}}
+    printf("%vd\n", arg); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 }
 
 kernel void format_v4f32_scalar(float arg)
@@ -142,7 +142,7 @@ kernel void format_v4f32_wrong_num_elts(float2 arg)
 
 kernel void format_missing_num_elts(float4 arg)
 {
-    printf("%vf\n", arg); // expected-warning {{incomplete format specifier}}
+    printf("%vf\n", arg); // expected-warning {{incomplete format specifier}} expected-warning{{data argument not used by format string}}
 }
 
 kernel void vector_precision_modifier_v4i32_to_v4f32(int4 arg)

``````````

</details>


https://github.com/llvm/llvm-project/pull/158514

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