[clang-tidy] modernize-use-std-format: Correct replacement types when signed stdint types are used, and when enums are printed in hex. #150343 #155200

DaveBrantonCTCT · 2025-08-25T03:46:24Z

These two examples illustrate the two problems

int8_t int_8_value;
printf("%d", int_8_value) ;

Will fail to replace correctly. The int8_t will cause this error message, and the replacement will be skipped.

Unknown corresponding signed type for non-BuiltinType 'int8_t'

SomeEnum enum_value;
printf("%x", enum_value) ;

This example will proceed with the replacement, but will fail to add the necessary cast to the enum's underlying type, and so the format string will break your build. That is, the replacement will be

SomeEnum enum_value;
fmt::print("{:x}", enum_value) ;

Instead of

SomeEnum enum_value;
fmt::print("{:x}", static_cast<int>(enum_value)) ;

Fixes #150343

github-actions · 2025-08-25T03:46:42Z

Thank you for submitting a Pull Request (PR) to the LLVM Project!

This PR will be automatically labeled and the relevant teams will be notified.

If you wish to, you can add reviewers by using the "Reviewers" section on this page.

If this is not working for you, it is probably because you do not have write permissions for the repository. In which case you can instead tag reviewers by name in a comment by using @ followed by their GitHub username.

If you have received no comments on your PR for a week, you can request a review by "ping"ing the PR by adding a comment “Ping”. The common courtesy "ping" rate is once a week. Please remember that you are asking for valuable time from other developers.

If you have further questions, they may be answered by the LLVM GitHub User Guide.

You can also ask questions in a comment on this PR, on the LLVM Discord or on the forums.

llvmbot · 2025-08-25T03:47:10Z

@llvm/pr-subscribers-clang-tools-extra

@llvm/pr-subscribers-clang-tidy

Author: None (DaveBrantonCTCT)

Changes

These two examples illustrate the two problems

int8_t int_8_value;
printf("%d", int_8_value) ;

Will fail to replace correctly. The int8_t will cause this error message, and the replacement will be skipped.

Unknown corresponding signed type for non-BuiltinType 'int8_t'

SomeEnum enum_value;
printf("%x", enum_value) ;

This example will proceed with the replacement, but will fail to add the necessary cast to the enum's underlying type, and so the format string will break your build. That is, the replacement will be

SomeEnum enum_value;
fmt::print("{:x}", enum_value) ;

Instead of

SomeEnum enum_value;
fmt::print("{:x}", static_cast&lt;int&gt;(enum_value)) ;
``

---
Full diff: https://github.com/llvm/llvm-project/pull/155200.diff


1 Files Affected:

- (modified) clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp (+68-11) 


``````````diff
diff --git a/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp b/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp
index 0df8e913100fc..76a14c5800589 100644
--- a/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp
+++ b/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp
@@ -42,7 +42,7 @@ static bool isRealCharType(const clang::QualType &Ty) {
 
 /// If possible, return the text name of the signed type that corresponds to the
 /// passed integer type. If the passed type is already signed then its name is
-/// just returned. Only supports BuiltinTypes.
+/// just returned. Supports BuiltinTypes and types from <cstdint>
 static std::optional<std::string>
 getCorrespondingSignedTypeName(const clang::QualType &QT) {
   using namespace clang;
@@ -80,6 +80,10 @@ getCorrespondingSignedTypeName(const clang::QualType &QT) {
   const bool InStd = SimplifiedTypeName.consume_front("std::");
   const StringRef Prefix = InStd ? "std::" : "";
 
+  if (SimplifiedTypeName.starts_with("int") &&
+      SimplifiedTypeName.ends_with("_t"))
+    return (Twine(Prefix) + SimplifiedTypeName).str();
+
   if (SimplifiedTypeName.starts_with("uint") &&
       SimplifiedTypeName.ends_with("_t"))
     return (Twine(Prefix) + SimplifiedTypeName.drop_front()).str();
@@ -453,8 +457,38 @@ bool FormatStringConverter::emitIntegerArgument(
     // std::format will print bool as either "true" or "false" by default,
     // but printf prints them as "0" or "1". Be compatible with printf by
     // requesting decimal output.
-    FormatSpec.push_back('d');
+
+    // In cases where `x` or `X` was specified in the format string
+    // these will technically have no effect, since the bool can only be zero or
+    // one. However, it seems best to leave them as-is anyway.
+    switch(ArgKind)
+    {
+      case ConversionSpecifier::Kind::xArg:
+        FormatSpec.push_back('x'); // Not strictly needed
+        break;
+      case ConversionSpecifier::Kind::XArg:
+        FormatSpec.push_back('X');
+        break;
+      default:
+        FormatSpec.push_back('d');
+    }
+    
   } else if (ArgType->isEnumeralType()) {
+
+    // If the format string contained `x` or `X`, then use these
+    // format modifiers. Otherwise the default will work.
+    switch(ArgKind)
+    {
+      case ConversionSpecifier::Kind::xArg:
+        FormatSpec.push_back('x');
+        break;
+      case ConversionSpecifier::Kind::XArg:
+        FormatSpec.push_back('X');
+        break;
+      default:
+        break;
+    }
+
     // std::format will try to find a specialization to print the enum
     // (and probably fail), whereas printf would have just expected it to
     // be passed as its underlying type. However, printf will have forced
@@ -478,8 +512,22 @@ bool FormatStringConverter::emitIntegerArgument(
     // unsigned unless we cast it.
     if (const std::optional<std::string> MaybeCastType =
             castTypeForArgument(ArgKind, ArgType))
+    {
+      switch(ArgKind)
+      {
+        case ConversionSpecifier::Kind::xArg:
+          FormatSpec.push_back('x');
+          break;
+        case ConversionSpecifier::Kind::XArg:
+          FormatSpec.push_back('X');
+          break;
+        default:
+          break;
+      }
+
       ArgFixes.emplace_back(
           ArgIndex, (Twine("static_cast<") + *MaybeCastType + ">(").str());
+    }
     else
       return conversionNotPossible(
           (Twine("argument ") + Twine(ArgIndex) + " cannot be cast to " +
@@ -488,9 +536,22 @@ bool FormatStringConverter::emitIntegerArgument(
            " integer type to match format"
            " specifier and StrictMode is enabled")
               .str());
-  } else if (isRealCharType(ArgType) || !ArgType->isIntegerType()) {
-    // Only specify integer if the argument is of a different type
-    FormatSpec.push_back('d');
+  } else
+  {
+    switch(ArgKind)
+    {
+      case ConversionSpecifier::Kind::xArg:
+        FormatSpec.push_back('x');
+        break;
+      case ConversionSpecifier::Kind::XArg:
+        FormatSpec.push_back('X');
+        break;
+      default:
+        if (isRealCharType(ArgType) || !ArgType->isIntegerType()) {
+        // Only specify integer if the argument is of a different type
+        FormatSpec.push_back('d');
+      }
+    }
   }
   return true;
 }
@@ -514,6 +575,8 @@ bool FormatStringConverter::emitType(const PrintfSpecifier &FS, const Expr *Arg,
   case ConversionSpecifier::Kind::dArg:
   case ConversionSpecifier::Kind::iArg:
   case ConversionSpecifier::Kind::uArg:
+  case ConversionSpecifier::Kind::xArg:
+  case ConversionSpecifier::Kind::XArg:
     if (!emitIntegerArgument(ArgKind, Arg, FS.getArgIndex() + ArgsOffset,
                              FormatSpec))
       return false;
@@ -526,12 +589,6 @@ bool FormatStringConverter::emitType(const PrintfSpecifier &FS, const Expr *Arg,
                             "static_cast<const void *>(");
     break;
   }
-  case ConversionSpecifier::Kind::xArg:
-    FormatSpec.push_back('x');
-    break;
-  case ConversionSpecifier::Kind::XArg:
-    FormatSpec.push_back('X');
-    break;
   case ConversionSpecifier::Kind::oArg:
     FormatSpec.push_back('o');
     break;

vbvictor

Please add tests and release notes about your change in clang-tools-extra/docs/ReleaseNotes.rst

github-actions · 2025-08-25T04:15:16Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff HEAD~1 HEAD --extensions cpp -- clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp

View the diff from clang-format here.

diff --git a/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp b/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp
index 76a14c580..104ce5eee 100644
--- a/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp
+++ b/clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp
@@ -461,32 +461,30 @@ bool FormatStringConverter::emitIntegerArgument(
     // In cases where `x` or `X` was specified in the format string
     // these will technically have no effect, since the bool can only be zero or
     // one. However, it seems best to leave them as-is anyway.
-    switch(ArgKind)
-    {
-      case ConversionSpecifier::Kind::xArg:
-        FormatSpec.push_back('x'); // Not strictly needed
-        break;
-      case ConversionSpecifier::Kind::XArg:
-        FormatSpec.push_back('X');
-        break;
-      default:
-        FormatSpec.push_back('d');
+    switch (ArgKind) {
+    case ConversionSpecifier::Kind::xArg:
+      FormatSpec.push_back('x'); // Not strictly needed
+      break;
+    case ConversionSpecifier::Kind::XArg:
+      FormatSpec.push_back('X');
+      break;
+    default:
+      FormatSpec.push_back('d');
     }
-    
+
   } else if (ArgType->isEnumeralType()) {
 
     // If the format string contained `x` or `X`, then use these
     // format modifiers. Otherwise the default will work.
-    switch(ArgKind)
-    {
-      case ConversionSpecifier::Kind::xArg:
-        FormatSpec.push_back('x');
-        break;
-      case ConversionSpecifier::Kind::XArg:
-        FormatSpec.push_back('X');
-        break;
-      default:
-        break;
+    switch (ArgKind) {
+    case ConversionSpecifier::Kind::xArg:
+      FormatSpec.push_back('x');
+      break;
+    case ConversionSpecifier::Kind::XArg:
+      FormatSpec.push_back('X');
+      break;
+    default:
+      break;
     }
 
     // std::format will try to find a specialization to print the enum
@@ -511,24 +509,21 @@ bool FormatStringConverter::emitIntegerArgument(
     // Even -Wformat doesn't warn for this. std::format will format as
     // unsigned unless we cast it.
     if (const std::optional<std::string> MaybeCastType =
-            castTypeForArgument(ArgKind, ArgType))
-    {
-      switch(ArgKind)
-      {
-        case ConversionSpecifier::Kind::xArg:
-          FormatSpec.push_back('x');
-          break;
-        case ConversionSpecifier::Kind::XArg:
-          FormatSpec.push_back('X');
-          break;
-        default:
-          break;
+            castTypeForArgument(ArgKind, ArgType)) {
+      switch (ArgKind) {
+      case ConversionSpecifier::Kind::xArg:
+        FormatSpec.push_back('x');
+        break;
+      case ConversionSpecifier::Kind::XArg:
+        FormatSpec.push_back('X');
+        break;
+      default:
+        break;
       }
 
       ArgFixes.emplace_back(
           ArgIndex, (Twine("static_cast<") + *MaybeCastType + ">(").str());
-    }
-    else
+    } else
       return conversionNotPossible(
           (Twine("argument ") + Twine(ArgIndex) + " cannot be cast to " +
            Twine(ArgKind == ConversionSpecifier::Kind::uArg ? "unsigned"
@@ -536,18 +531,16 @@ bool FormatStringConverter::emitIntegerArgument(
            " integer type to match format"
            " specifier and StrictMode is enabled")
               .str());
-  } else
-  {
-    switch(ArgKind)
-    {
-      case ConversionSpecifier::Kind::xArg:
-        FormatSpec.push_back('x');
-        break;
-      case ConversionSpecifier::Kind::XArg:
-        FormatSpec.push_back('X');
-        break;
-      default:
-        if (isRealCharType(ArgType) || !ArgType->isIntegerType()) {
+  } else {
+    switch (ArgKind) {
+    case ConversionSpecifier::Kind::xArg:
+      FormatSpec.push_back('x');
+      break;
+    case ConversionSpecifier::Kind::XArg:
+      FormatSpec.push_back('X');
+      break;
+    default:
+      if (isRealCharType(ArgType) || !ArgType->isIntegerType()) {
         // Only specify integer if the argument is of a different type
         FormatSpec.push_back('d');
       }

EugeneZelenko

Please mention changes in Release Notes.

EugeneZelenko · 2025-08-25T14:21:49Z

clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp

+    // In cases where `x` or `X` was specified in the format string
+    // these will technically have no effect, since the bool can only be zero or
+    // one. However, it seems best to leave them as-is anyway.
+    switch(ArgKind)


Please run Clang-Format.

EugeneZelenko · 2025-08-25T14:22:12Z

clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp

+        FormatSpec.push_back('X');
+        break;
+      default:
+        FormatSpec.push_back('d');


Suggested change

FormatSpec.push_back('d');

FormatSpec.push_back('d');

break;

EugeneZelenko · 2025-08-25T14:22:37Z

clang-tools-extra/clang-tidy/utils/FormatStringConverter.cpp

+        if (isRealCharType(ArgType) || !ArgType->isIntegerType()) {
+        // Only specify integer if the argument is of a different type
+        FormatSpec.push_back('d');
+      }


Suggested change

}

}

break;

…enums are printed in hex.

EugeneZelenko · 2025-09-01T21:13:03Z

llvm/docs/ReleaseNotes.md

@@ -150,6 +150,9 @@ Changes to the Debug Info
 Changes to the LLVM tools
 ---------------------------------

+* modernize-use-std-format now correctly replaces signed types, and correctly 


Such entry should be in clang-tools-extra/docs/ReleaseNotes.rst. See other entries there as examples.

Thank you, have put this in the right place.

EugeneZelenko · 2025-09-02T01:46:57Z

clang-tools-extra/docs/ReleaseNotes.rst

@@ -249,6 +249,10 @@ Changes in existing checks
  <clang-tidy/checks/readability/uppercase-literal-suffix>` check to recognize
  literal suffixes added in C++23 and C23.

+- Improved :doc:`modernize-use-std-format 


Please keep alphabetcial order (by check name) in this list.

EugeneZelenko · 2025-09-02T01:47:29Z

clang-tools-extra/docs/ReleaseNotes.rst

@@ -249,6 +249,10 @@ Changes in existing checks
  <clang-tidy/checks/readability/uppercase-literal-suffix>` check to recognize
  literal suffixes added in C++23 and C23.

+- Improved :doc:`modernize-use-std-format 
+  <clang-tidy/checks/modernize/use-std-format>` now correctly replaces signed types, and correctly 


Please follow 80 characters limit.

…ps://github.com/DaveBrantonCTCT/llvm-project into std-format-modernize-fix-enums-and-signed-types

EugeneZelenko · 2025-09-02T01:56:09Z

clang-tools-extra/docs/ReleaseNotes.rst

@@ -213,6 +213,11 @@ Changes in existing checks
  when the format string is converted to a different type by an implicit
  constructor call.

+- Improved :doc:`modernize-use-std-format 


Sorry, I missed existing modernize-use-std-format entry. Convention is to have single entry per check. Just merge existing statement with your text. At least previous release should have such examples.

vbvictor

Please write tests for your patch.

llvmbot added clang-tools-extra clang-tidy labels Aug 25, 2025

vbvictor reviewed Aug 25, 2025

View reviewed changes

EugeneZelenko reviewed Aug 25, 2025

View reviewed changes

EugeneZelenko requested review from PiotrZSL, carlosgalvezp, 5chmidti, localspook and HerrCai0907 August 25, 2025 14:24

Correct replacement code when signed stdint types are used, and when …

19b4ddf

…enums are printed in hex.

DaveBrantonCTCT force-pushed the std-format-modernize-fix-enums-and-signed-types branch from e37d17a to 19b4ddf Compare September 1, 2025 20:59

Added release notes

a85cce7

EugeneZelenko reviewed Sep 1, 2025

View reviewed changes

DaveBrantonCTCT added 2 commits September 2, 2025 10:52

Put docs in the right place

6dafba7

Merge branch 'main' into std-format-modernize-fix-enums-and-signed-types

a23e991

EugeneZelenko reviewed Sep 2, 2025

View reviewed changes

DaveBrantonCTCT added 3 commits September 2, 2025 13:48

Follow 80 character limit

49e42c1

Be alphabetical

4162ddc

Merge branch 'std-format-modernize-fix-enums-and-signed-types' of htt…

064cb9d

…ps://github.com/DaveBrantonCTCT/llvm-project into std-format-modernize-fix-enums-and-signed-types

EugeneZelenko reviewed Sep 2, 2025

View reviewed changes

Use existing entry

8514865

vbvictor requested changes Sep 5, 2025

View reviewed changes

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

[clang-tidy] modernize-use-std-format: Correct replacement types when signed stdint types are used, and when enums are printed in hex. #150343 #155200

[clang-tidy] modernize-use-std-format: Correct replacement types when signed stdint types are used, and when enums are printed in hex. #150343 #155200

DaveBrantonCTCT commented Aug 25, 2025 •

edited by vbvictor

Loading

Uh oh!

github-actions bot commented Aug 25, 2025

Uh oh!

llvmbot commented Aug 25, 2025 •

edited

Loading

Uh oh!

vbvictor left a comment

Uh oh!

github-actions bot commented Aug 25, 2025

Uh oh!

EugeneZelenko left a comment

Uh oh!

EugeneZelenko Aug 25, 2025

Uh oh!

EugeneZelenko Aug 25, 2025

Uh oh!

EugeneZelenko Aug 25, 2025

Uh oh!

EugeneZelenko Sep 1, 2025

Uh oh!

DaveBrantonCTCT Sep 2, 2025

Uh oh!

EugeneZelenko Sep 2, 2025

Uh oh!

EugeneZelenko Sep 2, 2025

Uh oh!

EugeneZelenko Sep 2, 2025

Uh oh!

vbvictor left a comment

Uh oh!

Uh oh!

[clang-tidy] modernize-use-std-format: Correct replacement types when signed stdint types are used, and when enums are printed in hex. #150343 #155200

Are you sure you want to change the base?

[clang-tidy] modernize-use-std-format: Correct replacement types when signed stdint types are used, and when enums are printed in hex. #150343 #155200

Conversation

DaveBrantonCTCT commented Aug 25, 2025 • edited by vbvictor Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

github-actions bot commented Aug 25, 2025

Uh oh!

llvmbot commented Aug 25, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

vbvictor left a comment

Choose a reason for hiding this comment

Uh oh!

github-actions bot commented Aug 25, 2025

Uh oh!

EugeneZelenko left a comment

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

Choose a reason for hiding this comment

Uh oh!

vbvictor left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

DaveBrantonCTCT commented Aug 25, 2025 •

edited by vbvictor

Loading

llvmbot commented Aug 25, 2025 •

edited

Loading