[clang-tidy] check `std::string_view` and custom string-like classes in `readability-string-compare` (#88636)

This PR aims to expand the list of classes that are considered to be
"strings" by `readability-string-compare` check.

1. Currently only `std::string;:compare` is checked, but
`std::string_view` has a similar `compare` method. This PR enables
checking of `std::string_view::compare` by default.
2. Some codebases use custom string-like classes that have public
interfaces similar to `std::string` or `std::string_view`. Example:
[TStringBase](https://github.com/yandex/yatool/blob/main/util/generic/strbase.h#L38),
A new option, `readability-string-compare.StringClassNames`, is added to
allow specifying a custom list of string-like classes.

Related to, but does not solve #28396 (only adds support for custom
string-like classes, not custom functions)

2 files changed, 58 insertions, 0 deletions

diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare-custom-string-classes.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare-custom-string-classes.cpp
new file mode 100644
index 0000000..faf1358
--- /dev/null
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare-custom-string-classes.cpp
@@ -0,0 +1,35 @@
+// RUN: %check_clang_tidy %s readability-string-compare %t -- -config='{CheckOptions: {readability-string-compare.StringLikeClasses: "CustomStringTemplateBase;CustomStringNonTemplateBase"}}' -- -isystem %clang_tidy_headers
+#include <string>
+
+struct CustomStringNonTemplateBase {
+  int compare(const CustomStringNonTemplateBase& Other) const {
+    return 123;  // value is not important for check
+  }
+};
+
+template <typename T>
+struct CustomStringTemplateBase {
+  int compare(const CustomStringTemplateBase& Other) const {
+    return 123;
+  }
+};
+
+struct CustomString1 : CustomStringNonTemplateBase {};
+struct CustomString2 : CustomStringTemplateBase<char> {};
+
+void CustomStringClasses() {
+  std::string_view sv1("a");
+  std::string_view sv2("b");
+  if (sv1.compare(sv2)) {  // No warning - if a std class is not listed in StringLikeClasses, it won't be checked.
+  }
+
+  CustomString1 custom1;
+  if (custom1.compare(custom1)) {
+  }
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: do not use 'compare' to test equality of strings; use the string equality operator instead [readability-string-compare]
+
+  CustomString2 custom2;
+  if (custom2.compare(custom2)) {
+  }
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: do not use 'compare' to test equality of strings; use the string equality operator instead [readability-string-compare]
+}
diff --git a/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare.cpp b/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare.cpp
index 2c08b86..c4fea43 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/readability/string-compare.cpp
@@ -67,11 +67,27 @@ void Test() {
   if (str1.compare(comp())) {
   }
   // CHECK-MESSAGES: [[@LINE-2]]:7: warning: do not use 'compare' to test equality of strings;
+
+  std::string_view sv1("a");
+  std::string_view sv2("b");
+  if (sv1.compare(sv2)) {
+  }
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: do not use 'compare' to test equality of strings; use the string equality operator instead [readability-string-compare]
+}
+
+struct DerivedFromStdString : std::string {};
+
+void TestDerivedClass() {
+  DerivedFromStdString derived;
+  if (derived.compare(derived)) {
+  }
+  // CHECK-MESSAGES: [[@LINE-2]]:7: warning: do not use 'compare' to test equality of strings; use the string equality operator instead [readability-string-compare]
 }
 
 void Valid() {
   std::string str1("a", 1);
   std::string str2("b", 1);
+
   if (str1 == str2) {
   }
   if (str1 != str2) {
@@ -96,4 +112,11 @@ void Valid() {
   }
   if (str1.compare(str2) == -1) {
   }
+
+  std::string_view sv1("a");
+  std::string_view sv2("b");
+  if (sv1 == sv2) {
+  }
+  if (sv1.compare(sv2) > 0) {
+  }
 }