[clang-tidy] Fix c_str() removal and cast addition when re-ordering arguments

[mikecrowe]

Summary

The modernize-use-std-print check would get confused if it had to
re-order field-width and precision arguments at the same time as adding
casts or removing calls to c_str().

Fix this by tracking the argument indices and combining c_str() removal
with argument re-ordering. Add missing test cases to lit check.

Fixes https://github.com/llvm/llvm-project/issues/64033

[mikecrowe]

Fixing this was rather messier than I expected, but this solution does seem to work for the test cases. Here's my original commit message before I trimmed it, in case it provides any more insight.

[clang-tidy] Fix c_str() removal and cast addition when re-ordering arguments

The modernize-use-std-print check would get confused if it had to
re-order field-width and precision arguments at the same time as adding
casts or removing calls to c_str(). For example applying the check with
StrictMode enabled to:

 printf("%*s=%*d\n", 4, s.c_str(), 3, ui);

yields:

 std::println("{:>{}}={:{}}", s.c_str(), s4, ui, static_cast<int>(3));

rather than the expected:

 std::println("{:>{}}={:{}}", s, 4, static_cast<int>(ui), 3);

Fix this by:

- storing the ArgIndex rather than the Expr pointer for any arguments
  that need casts to be added in ArgFixes so that the index can be
  modified when the arguments are re-ordered. Use a struct rather than a
  tuple for clarity.

- Making applyFixes do argument re-ordering first, but also taking care
  of c_str() removal at the same time if necessary. Update the argument
  index of any ArgFixes too.

- Apply the ArgFixes afterwards.

- Finally apply and c_str() removals that remain.

- Add lit check test cases for the combinations of argument reordering,
  casts and c_str() removal. This required moving the definition of
  struct iterator earlier in use-std-print.cpp.

[mikecrowe]

Rebase on top of D156616 and add more tests

[mikecrowe]

Reinstate version I incorrectly replaced with D154287

[mikecrowe]

@PiotrZSL, I think that this is quite an important fix since without it the check completely mangles the code. Should it be put in the 17.x release branch too?

[PiotrZSL]

In D156616#4621914, @mikecrowe wrote:

@PiotrZSL, I think that this is quite an important fix since without it the check completely mangles the code. Should it be put in the 17.x release branch too?

If issue happens only when StrictMode is set to True, then I wouldn't worry too much, and then this could wait for Clang 18 that is just half year away.

[mikecrowe]

In D156616#4621945, @PiotrZSL wrote:

In D156616#4621914, @mikecrowe wrote:

@PiotrZSL, I think that this is quite an important fix since without it the check completely mangles the code. Should it be put in the 17.x release branch too?

If issue happens only when StrictMode is set to True, then I wouldn't worry too much, and then this could wait for Clang 18 that is just half year away.

The removal of c_str() happens even without StrictMode set to True.

[PiotrZSL]

In D156616#4621975, @mikecrowe wrote:

The removal of c_str() happens even without StrictMode set to True.

I still think we will be fine. There are not many situations when arguments need to be reorder. And most probably not many users will change default configuration.
LLVM 17 is already past RC3, this issue is not critical, nor a regression, user can always disable check, or just manually fix few problematic cases in code.
Additionally user could always take "main" version, and use it just to apply fixes from this check.

[mikecrowe]

Additionally user could always take "main" version, and use it just to apply fixes from this check.

OK. Can this land on main then?

Thanks.

[mikecrowe]

Thanks for the review and landing this.

Mike.

clang-tools-extra/clang-tidy/modernize/CMakeLists.txt

add_clang_library(clangTidyModernizeModule
   UseDefaultMemberInitCheck.cpp
   UseEmplaceCheck.cpp
   UseEqualsDefaultCheck.cpp
   UseEqualsDeleteCheck.cpp
   UseNodiscardCheck.cpp
   UseNoexceptCheck.cpp
   UseNullptrCheck.cpp
   UseOverrideCheck.cpp
+  UseStdFormatCheck.cpp
   UseStdPrintCheck.cpp
   UseTrailingReturnTypeCheck.cpp
   UseTransparentFunctorsCheck.cpp
   UseUncaughtExceptionsCheck.cpp
   UseUsingCheck.cpp
 
   LINK_LIBS
   clangTidy

clang-tools-extra/clang-tidy/modernize/ModernizeTidyModule.cpp

 #include "UseDefaultMemberInitCheck.h"
 #include "UseEmplaceCheck.h"
 #include "UseEqualsDefaultCheck.h"
 #include "UseEqualsDeleteCheck.h"
 #include "UseNodiscardCheck.h"
 #include "UseNoexceptCheck.h"
 #include "UseNullptrCheck.h"
 #include "UseOverrideCheck.h"
+#include "UseStdFormatCheck.h"
 #include "UseStdPrintCheck.h"
 #include "UseTrailingReturnTypeCheck.h"
 #include "UseTransparentFunctorsCheck.h"
 #include "UseUncaughtExceptionsCheck.h"
 #include "UseUsingCheck.h"
 
 using namespace clang::ast_matchers;
 
CheckFactories.registerCheck<DeprecatedHeadersCheck>(
         "modernize-deprecated-headers");
     CheckFactories.registerCheck<DeprecatedIosBaseAliasesCheck>(
         "modernize-deprecated-ios-base-aliases");
     CheckFactories.registerCheck<LoopConvertCheck>("modernize-loop-convert");
     CheckFactories.registerCheck<MacroToEnumCheck>("modernize-macro-to-enum");
     CheckFactories.registerCheck<MakeSharedCheck>("modernize-make-shared");
     CheckFactories.registerCheck<MakeUniqueCheck>("modernize-make-unique");
     CheckFactories.registerCheck<PassByValueCheck>("modernize-pass-by-value");
+    CheckFactories.registerCheck<UseStdFormatCheck>("modernize-use-std-format");
     CheckFactories.registerCheck<UseStdPrintCheck>("modernize-use-std-print");
     CheckFactories.registerCheck<RawStringLiteralCheck>(
         "modernize-raw-string-literal");
     CheckFactories.registerCheck<RedundantVoidArgCheck>(
         "modernize-redundant-void-arg");
     CheckFactories.registerCheck<ReplaceAutoPtrCheck>(
         "modernize-replace-auto-ptr");
     CheckFactories.registerCheck<ReplaceDisallowCopyAndAssignMacroCheck>(

clang-tools-extra/clang-tidy/modernize/UseStdFormatCheck.h

+//===--- UseStdFormatCheck.h - clang-tidy -----------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USESTDFORMATCHECK_H
+#define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USESTDFORMATCHECK_H
+
+#include "../ClangTidyCheck.h"
+
+#include "../ClangTidyCheck.h"
+#include "../utils/IncludeInserter.h"
+
+namespace clang::tidy::modernize {
+
+/// Convert calls to absl::StrFormat-like functions to std::format.
+///
+/// For the user-facing documentation see:
+/// http://clang.llvm.org/extra/clang-tidy/checks/modernize/use-std-format.html
+class UseStdFormatCheck : public ClangTidyCheck {
+public:
+  UseStdFormatCheck(StringRef Name, ClangTidyContext *Context);
+  bool isLanguageVersionSupported(const LangOptions &LangOpts) const override {
+    if (ReplacementFormatFunction == "std::format")
+      return LangOpts.CPlusPlus20;
+    return LangOpts.CPlusPlus;
+  }
+  void registerPPCallbacks(const SourceManager &SM, Preprocessor *PP,
+                           Preprocessor *ModuleExpanderPP) override;
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
+  void registerMatchers(ast_matchers::MatchFinder *Finder) override;
+  void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+  std::optional<TraversalKind> getCheckTraversalKind() const override {
+    return TK_IgnoreUnlessSpelledInSource;
+  }
+
+private:
+  bool StrictMode;
+  std::vector<StringRef> StrFormatLikeFunctions;
+  StringRef ReplacementFormatFunction;
+  utils::IncludeInserter IncludeInserter;
+  std::optional<StringRef> MaybeHeaderToInclude;
+};
+
+} // namespace clang::tidy::modernize
+
+#endif // LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_MODERNIZE_USESTDFORMATCHECK_H

clang-tools-extra/clang-tidy/modernize/UseStdFormatCheck.cpp

+//===--- UseStdFormatCheck.cpp - clang-tidy -------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseStdFormatCheck.h"
+#include "../utils/FormatStringConverter.h"
+#include "../utils/Matchers.h"
+#include "../utils/OptionsUtils.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Lex/Lexer.h"
+#include "clang/Tooling/FixIt.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang::tidy::modernize {
+
+namespace {
+AST_MATCHER(StringLiteral, isOrdinary) { return Node.isOrdinary(); }
+} // namespace
+
+UseStdFormatCheck::UseStdFormatCheck(StringRef Name, ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      StrictMode(Options.getLocalOrGlobal("StrictMode", false)),
+      StrFormatLikeFunctions(utils::options::parseStringList(
+          Options.get("StrFormatLikeFunctions", ""))),
+      ReplacementFormatFunction(
+          Options.get("ReplacementFormatFunction", "std::format")),
+      IncludeInserter(Options.getLocalOrGlobal("IncludeStyle",
+                                               utils::IncludeSorter::IS_LLVM),
+                      areDiagsSelfContained()),
+      MaybeHeaderToInclude(Options.get("FormatHeader")) {
+  if (StrFormatLikeFunctions.empty())
+    StrFormatLikeFunctions.push_back("absl::StrFormat");
+
+  if (!MaybeHeaderToInclude && ReplacementFormatFunction == "std::format")
+    MaybeHeaderToInclude = "<format>";
+}
+
+void UseStdFormatCheck::registerPPCallbacks(const SourceManager &SM,
+                                            Preprocessor *PP,
+                                            Preprocessor *ModuleExpanderPP) {
+  IncludeInserter.registerPreprocessor(PP);
+}
+
+void UseStdFormatCheck::registerMatchers(MatchFinder *Finder) {
+  Finder->addMatcher(
+      callExpr(argumentCountAtLeast(1),
+               hasArgument(0, stringLiteral(isOrdinary())),
+               callee(functionDecl(unless(cxxMethodDecl()),
+                                   matchers::matchesAnyListedName(
+                                       StrFormatLikeFunctions))
+                          .bind("func_decl")))
+          .bind("strformat"),
+      this);
+}
+
+void UseStdFormatCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  using utils::options::serializeStringList;
+  Options.store(Opts, "StrictMode", StrictMode);
+  Options.store(Opts, "StrFormatLikeFunctions",
+                serializeStringList(StrFormatLikeFunctions));
+  Options.store(Opts, "ReplacementFormatFunction", ReplacementFormatFunction);
+  Options.store(Opts, "IncludeStyle", IncludeInserter.getStyle());
+  if (MaybeHeaderToInclude)
+    Options.store(Opts, "FormatHeader", *MaybeHeaderToInclude);
+}
+
+void UseStdFormatCheck::check(const MatchFinder::MatchResult &Result) {
+  const unsigned FormatArgOffset = 0;
+  const auto *OldFunction = Result.Nodes.getNodeAs<FunctionDecl>("func_decl");
+  const auto *StrFormat = Result.Nodes.getNodeAs<CallExpr>("strformat");
+
+  utils::FormatStringConverter::Configuration ConverterConfig;
+  ConverterConfig.StrictMode = StrictMode;
+  utils::FormatStringConverter Converter(Result.Context, StrFormat,
+                                         FormatArgOffset, ConverterConfig,
+                                         getLangOpts());
+  const Expr *StrFormatCall = StrFormat->getCallee();
+  if (!Converter.canApply()) {
+    DiagnosticBuilder Diag = diag(StrFormat->getBeginLoc(),
+                                  "unable to use '%0' instead of %1 because %2")
+                             << ReplacementFormatFunction
+                             << OldFunction->getIdentifier()
+                             << Converter.conversionNotPossibleReason();
+    return;
+  }
+
+  DiagnosticBuilder Diag =
+      diag(StrFormatCall->getBeginLoc(), "use '%0' instead of %1")
+      << ReplacementFormatFunction << OldFunction->getIdentifier();
+  Diag << FixItHint::CreateReplacement(
+      CharSourceRange::getTokenRange(StrFormatCall->getBeginLoc(),
+                                     StrFormatCall->getEndLoc()),
+      ReplacementFormatFunction);
+  Converter.applyFixes(Diag, *Result.SourceManager);
+
+  if (MaybeHeaderToInclude)
+    Diag << IncludeInserter.createIncludeInsertion(
+        Result.Context->getSourceManager().getFileID(
+            StrFormatCall->getBeginLoc()),
+        *MaybeHeaderToInclude);
+}
+
+} // namespace clang::tidy::modernize

clang-tools-extra/clang-tidy/modernize/UseStdPrintCheck.cpp

void UseStdPrintCheck::check(const MatchFinder::MatchResult &Result) {
   unsigned FormatArgOffset = 0;
   const auto *OldFunction = Result.Nodes.getNodeAs<FunctionDecl>("func_decl");
   const auto *Printf = Result.Nodes.getNodeAs<CallExpr>("printf");
   if (!Printf) {
     Printf = Result.Nodes.getNodeAs<CallExpr>("fprintf");
     FormatArgOffset = 1;
   }
 
+  utils::FormatStringConverter::Configuration ConverterConfig;
+  ConverterConfig.StrictMode = StrictMode;
+  ConverterConfig.AllowTrailingNewlineRemoval = true;
   utils::FormatStringConverter Converter(
-      Result.Context, Printf, FormatArgOffset, StrictMode, getLangOpts());
+      Result.Context, Printf, FormatArgOffset, ConverterConfig, getLangOpts());
   const Expr *PrintfCall = Printf->getCallee();
   const StringRef ReplacementFunction = Converter.usePrintNewlineFunction()
                                             ? ReplacementPrintlnFunction
                                             : ReplacementPrintFunction;
   if (!Converter.canApply()) {
     diag(PrintfCall->getBeginLoc(),
          "unable to use '%0' instead of %1 because %2")
         << ReplacementFunction << OldFunction->getIdentifier()

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

 /// compatibility. This class is expecting to work on the already-cooked format
 /// string (i.e. all the escapes have been converted) so we have to convert them
 /// back. This means that we might not convert them back using the same form.
 class FormatStringConverter
     : public clang::analyze_format_string::FormatStringHandler {
 public:
   using ConversionSpecifier = clang::analyze_format_string::ConversionSpecifier;
   using PrintfSpecifier = analyze_printf::PrintfSpecifier;
+
+  struct Configuration {
+    bool StrictMode = false;
+    bool AllowTrailingNewlineRemoval = false;
+  };
+
   FormatStringConverter(ASTContext *Context, const CallExpr *Call,
-                        unsigned FormatArgOffset, bool StrictMode,
+                        unsigned FormatArgOffset, Configuration Config,
                         const LangOptions &LO);
 
   bool canApply() const { return ConversionNotPossibleReason.empty(); }
   const std::string &conversionNotPossibleReason() const {
     return ConversionNotPossibleReason;
   }
   void applyFixes(DiagnosticBuilder &Diag, SourceManager &SM);
   bool usePrintNewlineFunction() const { return UsePrintNewlineFunction; }
 
 private:
   ASTContext *Context;
+  const Configuration Config;
   const bool CastMismatchedIntegerTypes;
   const Expr *const *Args;
   const unsigned NumArgs;
   unsigned ArgsOffset;
   const LangOptions &LangOpts;
   std::string ConversionNotPossibleReason;
   bool FormatStringNeededRewriting = false;
   bool UsePrintNewlineFunction = false;

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

if (StrictMode) {
     return FuncDecl->isVariadic();
   }
   return false;
 }
 
 FormatStringConverter::FormatStringConverter(ASTContext *ContextIn,
                                              const CallExpr *Call,
                                              unsigned FormatArgOffset,
-                                             bool StrictMode,
+                                             const Configuration ConfigIn,
                                              const LangOptions &LO)
-    : Context(ContextIn),
-      CastMismatchedIntegerTypes(castMismatchedIntegerTypes(Call, StrictMode)),
+    : Context(ContextIn), Config(ConfigIn),
+      CastMismatchedIntegerTypes(
+          castMismatchedIntegerTypes(Call, ConfigIn.StrictMode)),
       Args(Call->getArgs()), NumArgs(Call->getNumArgs()),
       ArgsOffset(FormatArgOffset + 1), LangOpts(LO) {
   assert(ArgsOffset <= NumArgs);
   FormatExpr = llvm::dyn_cast<StringLiteral>(
       Args[FormatArgOffset]->IgnoreImplicitAsWritten());
   assert(FormatExpr);
   if (!FormatExpr->isOrdinary())
     return; // No wide string support yet

 void FormatStringConverter::finalizeFormatText() {
   appendFormatText(
       StringRef(PrintfFormatString.begin() + PrintfFormatStringPos,
                 PrintfFormatString.size() - PrintfFormatStringPos));
   PrintfFormatStringPos = PrintfFormatString.size();
 
   // It's clearer to convert printf("Hello\r\n"); to std::print("Hello\r\n")
   // than to std::println("Hello\r");
-  if (StringRef(StandardFormatString).ends_with("\\n") &&
+  if (Config.AllowTrailingNewlineRemoval &&
+      StringRef(StandardFormatString).ends_with("\\n") &&
       !StringRef(StandardFormatString).ends_with("\\\\n") &&
       !StringRef(StandardFormatString).ends_with("\\r\\n")) {
     UsePrintNewlineFunction = true;
     FormatStringNeededRewriting = true;
     StandardFormatString.erase(StandardFormatString.end() - 2,
                                StandardFormatString.end());
   }
 

clang-tools-extra/docs/ReleaseNotes.rst

- New :doc:`performance-enum-size
   class based on the range of its enumerators.
 
 - New :doc:`readability-reference-to-constructed-temporary
   <clang-tidy/checks/readability/reference-to-constructed-temporary>` check.
 
   Detects C++ code where a reference variable is used to extend the lifetime
   of a temporary object that has just been constructed.
 
+- New :doc:`modernize-use-std-format
+  <clang-tidy/checks/modernize/use-std-format>` check.
+
+  Converts calls to ``absl::StrFormat``, or other functions via
+  configuration options, to C++20's ``std::format``, or another function
+  via a configuration option, modifying the format string appropriately and
+  removing now-unnecessary calls to ``std::string::c_str()`` and
+  ``std::string::data()``.
+
+
 New check aliases
 ^^^^^^^^^^^^^^^^^
 
 Changes in existing checks
 ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 - Fixed bug in :doc:`bugprone-reserved-identifier
   <clang-tidy/checks/bugprone/reserved-identifier>`, so that it does not warn

clang-tools-extra/docs/clang-tidy/checks/list.rst

.. csv-table::
    `modernize-use-default-member-init <modernize/use-default-member-init.html>`_, "Yes"
    `modernize-use-emplace <modernize/use-emplace.html>`_, "Yes"
    `modernize-use-equals-default <modernize/use-equals-default.html>`_, "Yes"
    `modernize-use-equals-delete <modernize/use-equals-delete.html>`_, "Yes"
    `modernize-use-nodiscard <modernize/use-nodiscard.html>`_, "Yes"
    `modernize-use-noexcept <modernize/use-noexcept.html>`_, "Yes"
    `modernize-use-nullptr <modernize/use-nullptr.html>`_, "Yes"
    `modernize-use-override <modernize/use-override.html>`_, "Yes"
+   `modernize-use-std-format <modernize/use-std-format.html>`_, "Yes"
    `modernize-use-std-print <modernize/use-std-print.html>`_, "Yes"
    `modernize-use-trailing-return-type <modernize/use-trailing-return-type.html>`_, "Yes"
    `modernize-use-transparent-functors <modernize/use-transparent-functors.html>`_, "Yes"
    `modernize-use-uncaught-exceptions <modernize/use-uncaught-exceptions.html>`_, "Yes"
    `modernize-use-using <modernize/use-using.html>`_, "Yes"
    `mpi-buffer-deref <mpi/buffer-deref.html>`_, "Yes"
    `mpi-type-mismatch <mpi/type-mismatch.html>`_, "Yes"
    `objc-assert-equals <objc/assert-equals.html>`_, "Yes"

clang-tools-extra/docs/clang-tidy/checks/modernize/use-std-format.rst

+.. title:: clang-tidy - modernize-use-std-format
+
+modernize-use-std-format
+========================
+
+Converts calls to ``absl::StrFormat``, or other functions via
+configuration options, to C++20's ``std::format``, or another function
+via a configuration option, modifying the format string appropriately and
+removing now-unnecessary calls to ``std::string::c_str()`` and
+``std::string::data()``.
+
+In other words, it turns lines like:
+
+.. code-block:: c++
+
+  return absl::StrFormat("The %s is %3d\n", description.c_str(), value);
+
+into:
+
+.. code-block:: c++
+
+  return std::format("The {} is {:3}", description, value);
+
+The check uses the same format-string-conversion algorithm as
+`modernize-use-std-print <../modernize/use-std-print.html>`_ and its
+shortcomings are described in the documentation for that check.
+
+Options
+-------
+
+.. option:: StrictMode
+
+   When `true`, the check will add casts when converting from variadic
+   functions and printing signed or unsigned integer types (including
+   fixed-width integer types from ``<cstdint>``, ``ptrdiff_t``, ``size_t``
+   and ``ssize_t``) as the opposite signedness to ensure that the output
+   would matches that of a simple wrapper for ``std::sprintf`` that
+   accepted a C-style variable argument list. For example, with
+   `StrictMode` enabled:
+
+  .. code-block:: c++
+
+    extern std::string strprintf(const char *format, ...);
+    int i = -42;
+    unsigned int u = 0xffffffff;
+    return strprintf("%d %u\n", i, u);
+
+  would be converted to:
+
+  .. code-block:: c++
+
+    return std::format("{} {}\n", static_cast<unsigned int>(i), static_cast<int>(u));
+
+  to ensure that the output will continue to be the unsigned representation
+  of -42 and the signed representation of 0xffffffff (often 4294967254
+  and -1 respectively.) When `false` (which is the default), these casts
+  will not be added which may cause a change in the output. Note that this
+  option makes no difference for the default value of
+  `StrFormatLikeFunctions` since ``absl::StrFormat`` takes a function
+  parameter pack and is not a variadic function.
+
+.. option:: StrFormatLikeFunctions
+
+   A semicolon-separated list of (fully qualified) extra function names to
+   replace, with the requirement that the first parameter contains the
+   printf-style format string and the arguments to be formatted follow
+   immediately afterwards. The default value for this option is
+   `absl::StrFormat`.
+
+.. option:: ReplacementFormatFunction
+
+   The function that will be used to replace the function set by the
+   `StrFormatLikeFunctions` option rather than the default
+   `std::format`. It is expected that the function provides an interface
+   that is compatible with ``std::format``. A suitable candidate would be
+   `fmt::format`.
+
+.. option:: FormatHeader
+
+   The header that must be included for the declaration of
+   `ReplacementFormatFunction` so that a ``#include`` directive can be added if
+   required. If `ReplacementFormatFunction` is `std::format` then this option will
+   default to ``<format>``, otherwise this option will default to nothing
+   and no ``#include`` directive will be added.

clang-tools-extra/test/clang-tidy/checkers/modernize/use-std-format-custom.cpp

+// RUN: %check_clang_tidy -check-suffixes=,STRICT \
+// RUN:   -std=c++20 %s modernize-use-std-format %t --      \
+// RUN:   -config="{CheckOptions: \
+// RUN:             [ \
+// RUN:              { \
+// RUN:                key: StrictMode, value: true \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.StrFormatLikeFunctions, \
+// RUN:               value: 'unqualified_strprintf;::strprintf; mynamespace::strprintf2' \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.ReplacementFormatFunction, \
+// RUN:               value: 'fmt::format' \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.FormatHeader, \
+// RUN:               value: '<fmt/core.h>' \
+// RUN:              } \
+// RUN:             ] \
+// RUN:            }" \
+// RUN:   -- -isystem %clang_tidy_headers
+// RUN: %check_clang_tidy -check-suffixes=,NOTSTRICT \
+// RUN:   -std=c++20 %s modernize-use-std-format %t --      \
+// RUN:   -config="{CheckOptions: \
+// RUN:             [ \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.StrFormatLikeFunctions, \
+// RUN:               value: '::strprintf; mynamespace::strprintf2' \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.ReplacementFormatFunction, \
+// RUN:               value: 'fmt::format' \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.FormatHeader, \
+// RUN:               value: '<fmt/core.h>' \
+// RUN:              } \
+// RUN:             ] \
+// RUN:            }" \
+// RUN:   -- -isystem %clang_tidy_headers
+
+#include <cstdio>
+#include <string>
+// CHECK-FIXES: #include <fmt/core.h>
+
+std::string strprintf(const char *, ...);
+
+namespace mynamespace {
+  std::string strprintf2(const char *, ...);
+}
+
+std::string strprintf_test(const std::string &name, double value) {
+  return strprintf("'%s'='%f'\n", name.c_str(), value);
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'fmt::format' instead of 'strprintf' [modernize-use-std-format]
+  // CHECK-FIXES: return fmt::format("'{}'='{:f}'\n", name, value);
+
+  return mynamespace::strprintf2("'%s'='%f'\n", name.c_str(), value);
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'fmt::format' instead of 'strprintf2' [modernize-use-std-format]
+  // CHECK-FIXES: return fmt::format("'{}'='{:f}'\n", name, value);
+}
+
+std::string StrFormat_strict_conversion() {
+  const unsigned char uc = 'A';
+  return strprintf("Integer %hhd from unsigned char\n", uc);
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'fmt::format' instead of 'strprintf' [modernize-use-std-format]
+  // CHECK-FIXES-NOTSTRICT: return fmt::format("Integer {} from unsigned char\n", uc);
+  // CHECK-FIXES-STRICT: return fmt::format("Integer {} from unsigned char\n", static_cast<signed char>(uc));
+}
+
+// Ensure that MatchesAnyListedNameMatcher::NameMatcher::match() can cope with a
+// NamedDecl that has no name when we're trying to match unqualified_strprintf.
+std::string A(const std::string &in)
+{
+    return "_" + in;
+}

clang-tools-extra/test/clang-tidy/checkers/modernize/use-std-format-fmt.cpp

+// RUN: %check_clang_tidy %s modernize-use-std-format %t -- \
+// RUN:   -config="{CheckOptions: \
+// RUN:             [ \
+// RUN:              { \
+// RUN:                key: StrictMode, value: true \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.StrFormatLikeFunctions, \
+// RUN:               value: 'fmt::sprintf' \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.ReplacementFormatFunction, \
+// RUN:               value: 'fmt::format' \
+// RUN:              }, \
+// RUN:              { \
+// RUN:               key: modernize-use-std-format.FormatHeader, \
+// RUN:               value: '<fmt/core.h>' \
+// RUN:              } \
+// RUN:             ] \
+// RUN:            }" \
+// RUN:   -- -isystem %clang_tidy_headers
+
+// CHECK-FIXES: #include <fmt/core.h>
+#include <string>
+
+namespace fmt
+{
+// Use const char * for the format since the real type is hard to mock up.
+template <typename... Args>
+std::string sprintf(const char *format, const Args&... args);
+} // namespace fmt
+
+std::string fmt_sprintf_simple() {
+  return fmt::sprintf("Hello %s %d", "world", 42);
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'fmt::format' instead of 'sprintf' [modernize-use-std-format]
+  // CHECK-FIXES: fmt::format("Hello {} {}", "world", 42);
+}

clang-tools-extra/test/clang-tidy/checkers/modernize/use-std-format.cpp

+// RUN: %check_clang_tidy \
+// RUN:   -std=c++20 %s modernize-use-std-format %t -- \
+// RUN:   -config="{CheckOptions: [{key: StrictMode, value: true}]}" \
+// RUN:   -- -isystem %clang_tidy_headers
+// RUN: %check_clang_tidy \
+// RUN:   -std=c++20 %s modernize-use-std-format %t -- \
+// RUN:   -config="{CheckOptions: [{key: StrictMode, value: false}]}" \
+// RUN:   -- -isystem %clang_tidy_headers
+#include <string>
+// CHECK-FIXES: #include <format>
+
+namespace absl
+{
+// Use const char * for the format since the real type is hard to mock up.
+template <typename... Args>
+std::string StrFormat(const char *format, const Args&... args);
+} // namespace absl
+
+template <typename T>
+struct iterator {
+  T *operator->();
+  T &operator*();
+};
+
+std::string StrFormat_simple() {
+  return absl::StrFormat("Hello");
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: return std::format("Hello");
+}
+
+std::string StrFormat_complex(const char *name, double value) {
+  return absl::StrFormat("'%s'='%f'", name, value);
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: return std::format("'{}'='{:f}'", name, value);
+}
+
+std::string StrFormat_integer_conversions() {
+  return absl::StrFormat("int:%d int:%d char:%c char:%c", 65, 'A', 66, 'B');
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: return std::format("int:{} int:{:d} char:{:c} char:{}", 65, 'A', 66, 'B');
+}
+
+// FormatConverter is capable of removing newlines from the end of the format
+// string. Ensure that isn't incorrectly happening for std::format.
+std::string StrFormat_no_newline_removal() {
+  return absl::StrFormat("a line\n");
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: return std::format("a line\n");
+}
+
+// FormatConverter is capable of removing newlines from the end of the format
+// string. Ensure that isn't incorrectly happening for std::format.
+std::string StrFormat_cstr_removal(const std::string &s1, const std::string *s2) {
+  return absl::StrFormat("%s %s %s %s", s1.c_str(), s1.data(), s2->c_str(), s2->data());
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: return std::format("{} {} {} {}", s1, s1, *s2, *s2);
+}
+
+std::string StrFormat_strict_conversion() {
+  const unsigned char uc = 'A';
+  return absl::StrFormat("Integer %hhd from unsigned char\n", uc);
+  // CHECK-MESSAGES: [[@LINE-1]]:10: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: return std::format("Integer {} from unsigned char\n", uc);
+}
+
+std::string StrFormat_field_width_and_precision() {
+  auto s1 = absl::StrFormat("width only:%*d width and precision:%*.*f precision only:%.*f", 3, 42, 4, 2, 3.14159265358979323846, 5, 2.718);
+  // CHECK-MESSAGES: [[@LINE-1]]:13: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: std::format("width only:{:{}} width and precision:{:{}.{}f} precision only:{:.{}f}", 42, 3, 3.14159265358979323846, 4, 2, 2.718, 5);
+
+  auto s2 = absl::StrFormat("width and precision positional:%1$*2$.*3$f after", 3.14159265358979323846, 4, 2);
+  // CHECK-MESSAGES: [[@LINE-1]]:13: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: std::format("width and precision positional:{0:{1}.{2}f} after", 3.14159265358979323846, 4, 2);
+
+  const int width = 10, precision = 3;
+  const unsigned int ui1 = 42, ui2 = 43, ui3 = 44;
+  auto s3 = absl::StrFormat("casts width only:%*d width and precision:%*.*d precision only:%.*d\n", 3, ui1, 4, 2, ui2, 5, ui3);
+  // CHECK-MESSAGES: [[@LINE-1]]:13: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES-NOTSTRICT: std::format("casts width only:{:{}} width and precision:{:{}.{}} precision only:{:.{}}", ui1, 3, ui2, 4, 2, ui3, 5);
+  // CHECK-FIXES-STRICT: std::format("casts width only:{:{}} width and precision:{:{}.{}} precision only:{:.{}}", static_cast<int>(ui1), 3, static_cast<int>(ui2), 4, 2, static_cast<int>(ui3), 5);
+
+  auto s4 = absl::StrFormat("c_str removal width only:%*s width and precision:%*.*s precision only:%.*s", 3, s1.c_str(), 4, 2, s2.c_str(), 5, s3.c_str());
+  // CHECK-MESSAGES: [[@LINE-1]]:13: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: std::format("c_str removal width only:{:>{}} width and precision:{:>{}.{}} precision only:{:.{}}", s1, 3, s2, 4, 2, s3, 5);
+
+  const std::string *ps1 = &s1, *ps2 = &s2, *ps3 = &s3;
+  auto s5 = absl::StrFormat("c_str() removal pointer width only:%-*s width and precision:%-*.*s precision only:%-.*s", 3, ps1->c_str(), 4, 2, ps2->c_str(), 5, ps3->c_str());
+  // CHECK-MESSAGES: [[@LINE-1]]:13: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: std::format("c_str() removal pointer width only:{:{}} width and precision:{:{}.{}} precision only:{:.{}}", *ps1, 3, *ps2, 4, 2, *ps3, 5);
+
+  iterator<std::string> is1, is2, is3;
+  auto s6 = absl::StrFormat("c_str() removal iterator width only:%-*s width and precision:%-*.*s precision only:%-.*s", 3, is1->c_str(), 4, 2, is2->c_str(), 5, is3->c_str());
+  // CHECK-MESSAGES: [[@LINE-1]]:13: warning: use 'std::format' instead of 'StrFormat' [modernize-use-std-format]
+  // CHECK-FIXES: std::format("c_str() removal iterator width only:{:{}} width and precision:{:{}.{}} precision only:{:.{}}", *is1, 3, *is2, 4, 2, *is3, 5);
+
+  return s1 + s2 + s3 + s4 + s5 + s6;
+}