[clang-tidy] Add option to ignore user-defined literals in readability-magic-numbers

Some user-defined literals operate on implementation-defined types, like
"unsigned long long" and "long double", which are not well supported by
this check. Currently, the check gives warnings when using UDLs, without
giving possiblity to the user to whitelist common UDLs. A good compromise
until a proper fix is found (if any) is to allow the user to disable
warnings on UDLs.

Partially fixes #61656

Differential Revision: https://reviews.llvm.org/D146913

clang-tools-extra/clang-tidy/readability/MagicNumbersCheck.cpp

@@ -81,6 +81,8 @@ MagicNumbersCheck::MagicNumbersCheck(StringRef Name, ClangTidyContext *Context)
       IgnorePowersOf2IntegerValues(
           Options.get("IgnorePowersOf2IntegerValues", false)),
       IgnoreTypeAliases(Options.get("IgnoreTypeAliases", false)),
+      IgnoreUserDefinedLiterals(
+          Options.get("IgnoreUserDefinedLiterals", false)),
       RawIgnoredIntegerValues(
           Options.get("IgnoredIntegerValues", DefaultIgnoredIntegerValues)),
       RawIgnoredFloatingPointValues(Options.get(
@@ -130,6 +132,7 @@ void MagicNumbersCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
   Options.store(Opts, "IgnorePowersOf2IntegerValues",
                 IgnorePowersOf2IntegerValues);
   Options.store(Opts, "IgnoreTypeAliases", IgnoreTypeAliases);
+  Options.store(Opts, "IgnoreUserDefinedLiterals", IgnoreUserDefinedLiterals);
   Options.store(Opts, "IgnoredIntegerValues", RawIgnoredIntegerValues);
   Options.store(Opts, "IgnoredFloatingPointValues",
                 RawIgnoredFloatingPointValues);
@@ -243,5 +246,14 @@ bool MagicNumbersCheck::isBitFieldWidth(
                       });
 }
 
+bool MagicNumbersCheck::isUserDefinedLiteral(
+    const clang::ast_matchers::MatchFinder::MatchResult &Result,
+    const clang::Expr &Literal) const {
+  DynTypedNodeList Parents = Result.Context->getParents(Literal);
+  if (Parents.empty())
+    return false;
+  return Parents[0].get<UserDefinedLiteral>() != nullptr;
+}
+
 } // namespace tidy::readability
 } // namespace clang

clang-tools-extra/clang-tidy/readability/MagicNumbersCheck.h

@@ -49,6 +49,10 @@ private:
   bool isBitFieldWidth(const clang::ast_matchers::MatchFinder::MatchResult &Result,
                        const IntegerLiteral &Literal) const;
 
+  bool isUserDefinedLiteral(
+      const clang::ast_matchers::MatchFinder::MatchResult &Result,
+      const clang::Expr &Literal) const;
+
   template <typename L>
   void checkBoundMatch(const ast_matchers::MatchFinder::MatchResult &Result,
                        const char *BoundName) {
@@ -72,6 +76,10 @@ private:
     if (isBitFieldWidth(Result, *MatchedLiteral))
       return;
 
+    if (IgnoreUserDefinedLiterals &&
+        isUserDefinedLiteral(Result, *MatchedLiteral))
+      return;
+
     const StringRef LiteralSourceText = Lexer::getSourceText(
         CharSourceRange::getTokenRange(MatchedLiteral->getSourceRange()),
         *Result.SourceManager, getLangOpts());
@@ -85,6 +93,7 @@ private:
   const bool IgnoreBitFieldsWidths;
   const bool IgnorePowersOf2IntegerValues;
   const bool IgnoreTypeAliases;
+  const bool IgnoreUserDefinedLiterals;
   const StringRef RawIgnoredIntegerValues;
   const StringRef RawIgnoredFloatingPointValues;
 

clang-tools-extra/docs/ReleaseNotes.rst

@@ -223,6 +223,9 @@ Changes in existing checks
   behavior of using `i` as the prefix for enum tags, set the `EnumConstantPrefix`
   option to `i` instead of using `EnumConstantHungarianPrefix`.
 
+- Added support to optionally ignore user-defined literals in
+  :doc:`readability-magic-numbers<clang-tidy/checks/readability/magic-numbers>`.
+
 - Fixed a false positive in :doc:`readability-container-size-empty
   <clang-tidy/checks/readability/container-size-empty>` check when comparing
   ``std::array`` objects to default constructed ones. The behavior for this and

clang-tools-extra/docs/clang-tidy/checks/readability/magic-numbers.rst

@@ -57,7 +57,7 @@ Example with magic values refactored:
 
    const size_t NUMBER_OF_ELEMENTS = 30;
    using containerType = CustomType<int, NUMBER_OF_ELEMENTS>;
-   
+
    struct OtherType {
       containerType container;
    }
@@ -144,3 +144,8 @@ Options
 
    Boolean value indicating whether to accept magic numbers in ``typedef`` or
    ``using`` declarations. Default value is `false`.
+
+.. option:: IgnoreUserDefinedLiterals
+
+   Boolean value indicating whether to accept magic numbers in user-defined
+   literals. Default value is `false`.

clang-tools-extra/test/clang-tidy/checkers/readability/magic-numbers-userliteral.cpp

@@ -1,10 +1,18 @@
-// RUN: %check_clang_tidy -std=c++14-or-later %s readability-magic-numbers %t --
+// RUN: %check_clang_tidy -check-suffixes=UDL-ALLOWED -std=c++14-or-later %s readability-magic-numbers %t \
+// RUN: -config='{CheckOptions: \
+// RUN:  [{key: readability-magic-numbers.IgnoreUserDefinedLiterals, value: false}]}' \
+// RUN: --
+// RUN: %check_clang_tidy -check-suffixes=UDL-IGNORED -std=c++14-or-later %s readability-magic-numbers %t \
+// RUN: -config='{CheckOptions: \
+// RUN:  [{key: readability-magic-numbers.IgnoreUserDefinedLiterals, value: true}]}' \
+// RUN: --
 
 namespace std {
   class string {};
   using size_t = decltype(sizeof(int));
   string operator ""s(const char *, std::size_t);
   int operator "" s(unsigned long long);
+  float operator "" s(long double);
 }
 
 void UserDefinedLiteral() {
@@ -12,5 +20,9 @@ void UserDefinedLiteral() {
   "Hello World"s;
   const int i = 3600s;
   int j = 3600s;
-  // CHECK-MESSAGES: :[[@LINE-1]]:11: warning: 3600s is a magic number; consider replacing it with a named constant [readability-magic-numbers]
+  // CHECK-MESSAGES-UDL-ALLOWED: :[[@LINE-1]]:11: warning: 3600s is a magic number; consider replacing it with a named constant [readability-magic-numbers]
+  // CHECK-MESSAGES-UDL-IGNORED-NOT: :[[@LINE-2]]:11: warning: 3600s is a magic number; consider replacing it with a named constant [readability-magic-numbers]
+  float k = 3600.0s;
+  // CHECK-MESSAGES-UDL-ALLOWED: :[[@LINE-1]]:13: warning: 3600.0s is a magic number; consider replacing it with a named constant [readability-magic-numbers]
+  // CHECK-MESSAGES-UDL-IGNORED-NOT: :[[@LINE-1]]:13: warning: 3600.0s is a magic number; consider replacing it with a named constant [readability-magic-numbers]
 }