[clang-tidy] Improve string type matcher for abseil-string-find-starts-with check.

[hokein]

Summary

This patch improves the check to match the desugared "string" type (so that it
can handle custom-implemented string classes), see the newly-added test.

[alexfh]

LG

clang-tidy/abseil/StringFindStartswithCheck.cpp

: ClangTidyCheck(Name, Context),
           Options.getLocalOrGlobal("IncludeStyle", "llvm"))),
       AbseilStringsMatchHeader(
           Options.get("AbseilStringsMatchHeader", "absl/strings/match.h")) {}
 
 void StringFindStartswithCheck::registerMatchers(MatchFinder *Finder) {
   auto ZeroLiteral = integerLiteral(equals(0));
   auto StringClassMatcher = cxxRecordDecl(hasAnyName(SmallVector<StringRef, 4>(
       StringLikeClasses.begin(), StringLikeClasses.end())));
+  auto StringType = hasUnqualifiedDesugaredType(
+      recordType(hasDeclaration(StringClassMatcher)));
 
   auto StringFind = cxxMemberCallExpr(
       // .find()-call on a string...
-      callee(cxxMethodDecl(hasName("find"), ofClass(StringClassMatcher))),
+      callee(cxxMethodDecl(hasName("find"))),
+      on(hasType(StringType)),
       // ... with some search expression ...
       hasArgument(0, expr().bind("needle")),
       // ... and either "0" as second argument or the default argument (also 0).
       anyOf(hasArgument(1, ZeroLiteral), hasArgument(1, cxxDefaultArgExpr())));
 
   Finder->addMatcher(
       // Match [=!]= with a zero on one side and a string.find on the other.
       binaryOperator(

test/clang-tidy/abseil-string-find-startswith.cpp

-// RUN: %check_clang_tidy %s abseil-string-find-startswith %t
+// RUN: %check_clang_tidy %s abseil-string-find-startswith %t -- \
+// RUN:   -config="{CheckOptions: [{key: 'abseil-string-find-startswith.StringLikeClasses', value: '::std::basic_string;::basic_string'}]}" \
+// RUN:   -- -std=c++11
 
 namespace std {
 template <typename T> class allocator {};
 template <typename T> class char_traits {};
 template <typename C, typename T = std::char_traits<C>,
           typename A = std::allocator<C>>
 struct basic_string {
   basic_string();
   basic_string(const basic_string &);
   basic_string(const C *, const A &a = A());
   ~basic_string();
   int find(basic_string<C> s, int pos = 0);
   int find(const char *s, int pos = 0);
 };
 typedef basic_string<char> string;
 typedef basic_string<wchar_t> wstring;
+
+struct cxx_string {
+  int find(const char *s, int pos = 0);
+};
 } // namespace std
 
+struct basic_string : public std::cxx_string {
+  basic_string();
+};
+typedef basic_string global_string;
+
 std::string foo(std::string);
 std::string bar();
 
 #define A_MACRO(x, y) ((x) == (y))
 
-void tests(std::string s) {
+void tests(std::string s, global_string s2) {
   s.find("a") == 0;
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use absl::StartsWith instead of find() == 0 [abseil-string-find-startswith]
   // CHECK-FIXES: {{^[[:space:]]*}}absl::StartsWith(s, "a");{{$}}
 
   s.find(s) == 0;
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use absl::StartsWith
   // CHECK-FIXES: {{^[[:space:]]*}}absl::StartsWith(s, s);{{$}}
 
   s.find("aaa") != 0;
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use !absl::StartsWith
   // CHECK-FIXES: {{^[[:space:]]*}}!absl::StartsWith(s, "aaa");{{$}}
 
   s.find(foo(foo(bar()))) != 0;
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use !absl::StartsWith
   // CHECK-FIXES: {{^[[:space:]]*}}!absl::StartsWith(s, foo(foo(bar())));{{$}}
 
   if (s.find("....") == 0) { /* do something */ }
   // CHECK-MESSAGES: :[[@LINE-1]]:7: warning: use absl::StartsWith
   // CHECK-FIXES: {{^[[:space:]]*}}if (absl::StartsWith(s, "....")) { /* do something */ }{{$}}
 
   0 != s.find("a");
   // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use !absl::StartsWith
   // CHECK-FIXES: {{^[[:space:]]*}}!absl::StartsWith(s, "a");{{$}}
 
+  s2.find("a") == 0;
+  // CHECK-MESSAGES: :[[@LINE-1]]:3: warning: use absl::StartsWith
+  // CHECK-FIXES: {{^[[:space:]]*}}absl::StartsWith(s2, "a");{{$}}
+
   // expressions that don't trigger the check are here.
   A_MACRO(s.find("a"), 0);
   s.find("a", 1) == 0;
   s.find("a", 1) == 1;
   s.find("a") == 1;
 }