[clang-tidy] readability-container-size-empty - detect missing usage of .empty() on string_literals

[felix642]

Summary

Detect comparison between string and empty string_literals.

Fixes #64547

[PiotrZSL]

• Release notes entry is missing.
• Commit/Change description should be updated

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

171

Probably best would be to write matcher like this:

AST_MATCHER_P(UserDefinedLiteral, hasLiteral, Matcher<Expr>, InnerMatcher) {
   if (const Expr* CookedLiteral  = Node.getCookedLiteral()) {
      return InnerMatcher.matches(CookedLiteral, Finder, Builder);
   }
   return false;
}

and use it instead of hasDescendant

userDefinedLiteral(hasLiteral(stringLiteral(hasSize(0)))),

clang-tools-extra/test/clang-tidy/checkers/readability/container-size-empty.cpp

791

Add this new line

[felix642]

Fixed tests and addressed comments.

[felix642]

Hi @PiotrZSL, thank you for the feedback.

I have addressed most of your comments, but I'm not sure to understand what you mean by "Commit/Change description should be updated". Would you be able to clarify that for me?

[PiotrZSL]

LGTM, run clang-format on this code....

[felix642]

Clang-format

[rnk]

clang-tools-extra/test/clang-tidy/checkers/readability/container-size-empty.cpp

26

I discovered that this test started to fail when I landed my revert (0d9919d362a7a70b2a7970861d897ecc47ec9e4d) of f2583f3acf596cc545c8c0e3cb28e712f4ebf21b. I "fixed" the test by changing this to operator""_s in ba52a10fca6fc7b791894c584233db012def68a5, but I'm not sure if that changes the meaning of the test. Please review that or follow up on this.

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

Finder->addMatcher(
                    hasMemberName("size"))),
                WrongUse,
                unless(hasAncestor(
                    cxxMethodDecl(ofClass(equalsBoundNode("container"))))))
           .bind("SizeCallExpr"),
       this);
 
   // Comparison to empty string or empty constructor.
-  const auto WrongComparend = anyOf(
-      stringLiteral(hasSize(0)), cxxConstructExpr(isDefaultConstruction()),
+  const auto WrongComparend =
+      anyOf(stringLiteral(hasSize(0)),
+            userDefinedLiteral(hasDescendant(stringLiteral(hasSize(0)))),
+            cxxConstructExpr(isDefaultConstruction()),
             cxxUnresolvedConstructExpr(argumentCountIs(0)));
   // Match the object being compared.
   const auto STLArg =
       anyOf(unaryOperator(
                 hasOperatorName("*"),
                 hasUnaryOperand(
                     expr(hasType(pointsTo(ValidContainer))).bind("Pointee"))),
             expr(hasType(ValidContainer)).bind("STLObject"));
 

clang-tools-extra/test/clang-tidy/checkers/readability/container-size-empty.cpp

template <typename T> struct set {
   set();
   bool operator==(const set<T>& other) const;
   bool operator!=(const set<T>& other) const;
   unsigned long size() const;
   bool empty() const;
 };
 }
 
+namespace string_literals{
+string operator""s(const char *, size_t);
+}
+
 }
 
 template <typename T>
 class TemplatedContainer {
 public:
   bool operator==(const TemplatedContainer<T>& other) const;
   bool operator!=(const TemplatedContainer<T>& other) const;
   int size() const;

 // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: the 'empty' method should be used to check for emptiness instead of comparing to an empty object [readability-container-size-empty]
 // CHECK-FIXES: {{^  }}return value.empty();{{$}}
 // CHECK-MESSAGES: :741:8: note: method 'DummyType'::empty() defined here
 }
 
 bool testIgnoredDummyType(const IgnoredDummyType& value) {
   return value == IgnoredDummyType();
 }
+
+bool testStringLiterals(const std::string& s)
+{
+  using namespace std::string_literals;
+  return s == ""s;
+  // CHECK-MESSAGES: :[[@LINE-1]]:10: warning: the 'empty' method should be used
+  // CHECK-FIXES: {{^  }}return s.empty()
+}
+
+bool testNotEmptyStringLiterals(const std::string& s)
+{
+  using namespace std::string_literals;
+  return s == "foo"s;
+}
 No newline at end of file