[clang-tidy] Give readability-redundant-string-init a customizable list of string types to fix

Summary:
This patch adds a feature requested in https://reviews.llvm.org/D69238 to enable `readability-redundant-string-init` to take a list of strings to apply the fix to rather than hard-coding `basic_string`. It adds a `StringNames` option of semicolon-delimited names of string classes to which to apply this fix. Tests ensure this works with test class out::TestString as well as std::string and std::wstring as before. It should be applicable to llvm::StringRef, QString, etc.

Note: This commit was previously reverted due to a failing unit test. That test has been fixed in this version.

Reviewers: MyDeveloperDay, aaron.ballman, hokein, alexfh, JonasToth, gribozavr2

Patch by: poelmanc

Subscribers: gribozavr2, xazax.hun, Eugene.Zelenko, cfe-commits

Tags: #clang-tools-extra, #clang

Differential Revision: https://reviews.llvm.org/D69548

Author: Mitchell Balan

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

@@ -8,6 +8,7 @@
 
 #include "RedundantStringInitCheck.h"
 #include "../utils/Matchers.h"
+#include "../utils/OptionsUtils.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
 
 using namespace clang::ast_matchers;
@@ -17,19 +18,43 @@ namespace clang {
 namespace tidy {
 namespace readability {
 
+const char DefaultStringNames[] = "::std::basic_string";
+
+RedundantStringInitCheck::RedundantStringInitCheck(StringRef Name,
+                                                   ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context),
+      StringNames(utils::options::parseStringList(
+          Options.get("StringNames", DefaultStringNames))) {}
+
+void RedundantStringInitCheck::storeOptions(ClangTidyOptions::OptionMap &Opts) {
+  Options.store(Opts, "StringNames", DefaultStringNames);
+}
+
 void RedundantStringInitCheck::registerMatchers(MatchFinder *Finder) {
   if (!getLangOpts().CPlusPlus)
     return;
+  const auto hasStringTypeName = hasAnyName(
+      SmallVector<StringRef, 3>(StringNames.begin(), StringNames.end()));
+
+  // Version of StringNames with namespaces removed
+  std::vector<std::string> stringNamesNoNamespace;
+  for (const std::string &name : StringNames) {
+    std::string::size_type colonPos = name.rfind(':');
+    stringNamesNoNamespace.push_back(
+        name.substr(colonPos == std::string::npos ? 0 : colonPos + 1));
+  }
+  const auto hasStringCtorName = hasAnyName(SmallVector<StringRef, 3>(
+      stringNamesNoNamespace.begin(), stringNamesNoNamespace.end()));
 
   // Match string constructor.
-  const auto StringConstructorExpr = expr(anyOf(
-      cxxConstructExpr(argumentCountIs(1),
-                       hasDeclaration(cxxMethodDecl(hasName("basic_string")))),
-      // If present, the second argument is the alloc object which must not
-      // be present explicitly.
-      cxxConstructExpr(argumentCountIs(2),
-                       hasDeclaration(cxxMethodDecl(hasName("basic_string"))),
-                       hasArgument(1, cxxDefaultArgExpr()))));
+  const auto StringConstructorExpr = expr(
+      anyOf(cxxConstructExpr(argumentCountIs(1),
+                             hasDeclaration(cxxMethodDecl(hasStringCtorName))),
+            // If present, the second argument is the alloc object which must
+            // not be present explicitly.
+            cxxConstructExpr(argumentCountIs(2),
+                             hasDeclaration(cxxMethodDecl(hasStringCtorName)),
+                             hasArgument(1, cxxDefaultArgExpr()))));
 
   // Match a string constructor expression with an empty string literal.
   const auto EmptyStringCtorExpr = cxxConstructExpr(
@@ -48,7 +73,7 @@ void RedundantStringInitCheck::registerMatchers(MatchFinder *Finder) {
       namedDecl(
           varDecl(
               hasType(hasUnqualifiedDesugaredType(recordType(
-                  hasDeclaration(cxxRecordDecl(hasName("basic_string")))))),
+                  hasDeclaration(cxxRecordDecl(hasStringTypeName))))),
               hasInitializer(expr(ignoringImplicit(anyOf(
                   EmptyStringCtorExpr, EmptyStringCtorExprWithTemporaries)))))
               .bind("vardecl"),

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

@@ -10,6 +10,8 @@
 #define LLVM_CLANG_TOOLS_EXTRA_CLANG_TIDY_READABILITY_REDUNDANT_STRING_INIT_H
 
 #include "../ClangTidyCheck.h"
+#include <string>
+#include <vector>
 
 namespace clang {
 namespace tidy {
@@ -18,10 +20,13 @@ namespace readability {
 /// Finds unnecessary string initializations.
 class RedundantStringInitCheck : public ClangTidyCheck {
 public:
-  RedundantStringInitCheck(StringRef Name, ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context) {}
+  RedundantStringInitCheck(StringRef Name, ClangTidyContext *Context);
+  void storeOptions(ClangTidyOptions::OptionMap &Opts) override;
   void registerMatchers(ast_matchers::MatchFinder *Finder) override;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) override;
+
+private:
+  std::vector<std::string> StringNames;
 };
 
 } // namespace readability

clang-tools-extra/docs/ReleaseNotes.rst

@@ -170,6 +170,10 @@ Improvements to clang-tidy
   The check now supports the ``AllowOverrideAndFinal`` option to eliminate
   conflicts with ``gcc -Wsuggest-override`` or ``gcc -Werror=suggest-override``.
 
+- The :doc:`readability-redundant-string-init
+  <clang-tidy/checks/readability-redundant-string-init>` check now supports a
+  `StringNames` option enabling its application to custom string classes.
+
 Improvements to include-fixer
 -----------------------------
 

clang-tools-extra/docs/clang-tidy/checks/readability-redundant-string-init.rst

@@ -5,7 +5,8 @@ readability-redundant-string-init
 
 Finds unnecessary string initializations.
 
-Examples:
+Examples
+--------
 
 .. code-block:: c++
 
@@ -17,3 +18,15 @@ Examples:
 
   std::string a;
   std::string b;
+
+Options
+-------
+
+.. option:: StringNames
+
+    Default is `::std::basic_string`.
+
+    Semicolon-delimited list of class names to apply this check to.
+    By default `::std::basic_string` applies to ``std::string`` and
+    ``std::wstring``. Set to e.g. `::std::basic_string;llvm::StringRef;QString`
+    to perform this check on custom classes.

clang-tools-extra/test/clang-tidy/checkers/readability-redundant-string-init.cpp

@@ -1,4 +1,9 @@
-// RUN: %check_clang_tidy %s readability-redundant-string-init %t
+// RUN: %check_clang_tidy -std=c++11,c++14 %s readability-redundant-string-init %t \
+// RUN:   -config="{CheckOptions: \
+// RUN:             [{key: readability-redundant-string-init.StringNames, \
+// RUN:               value: '::std::basic_string;our::TestString'}] \
+// RUN:             }"
+// FIXME: Fix the checker to work in C++17 mode.
 
 namespace std {
 template <typename T>
@@ -143,3 +148,82 @@ extern void Param2(const std::string& param = "");
 void Param3(std::string param = "") {}
 void Param4(STRING param = "") {}
 
+namespace our {
+struct TestString {
+  TestString();
+  TestString(const TestString &);
+  TestString(const char *);
+  ~TestString();
+};
+}
+
+void ourTestStringTests() {
+  our::TestString a = "";
+  // CHECK-MESSAGES: [[@LINE-1]]:19: warning: redundant string initialization
+  // CHECK-FIXES: our::TestString a;
+  our::TestString b("");
+  // CHECK-MESSAGES: [[@LINE-1]]:19: warning: redundant string initialization
+  // CHECK-FIXES: our::TestString b;
+  our::TestString c = R"()";
+  // CHECK-MESSAGES: [[@LINE-1]]:19: warning: redundant string initialization
+  // CHECK-FIXES: our::TestString c;
+  our::TestString d(R"()");
+  // CHECK-MESSAGES: [[@LINE-1]]:19: warning: redundant string initialization
+  // CHECK-FIXES: our::TestString d;
+
+  our::TestString u = "u";
+  our::TestString w("w");
+  our::TestString x = R"(x)";
+  our::TestString y(R"(y)");
+  our::TestString z;
+}
+
+namespace their {
+using TestString = our::TestString;
+}
+
+// their::TestString is the same type so should warn / fix
+void theirTestStringTests() {
+  their::TestString a = "";
+  // CHECK-MESSAGES: [[@LINE-1]]:21: warning: redundant string initialization
+  // CHECK-FIXES: their::TestString a;
+  their::TestString b("");
+  // CHECK-MESSAGES: [[@LINE-1]]:21: warning: redundant string initialization
+  // CHECK-FIXES: their::TestString b;
+}
+
+namespace other {
+// Identical declarations to above but different type
+struct TestString {
+  TestString();
+  TestString(const TestString &);
+  TestString(const char *);
+  ~TestString();
+};
+
+// Identical declarations to above but different type
+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();
+};
+typedef basic_string<char> string;
+typedef basic_string<wchar_t> wstring;
+}
+
+// other::TestString, other::string, other::wstring are unrelated to the types
+// being checked. No warnings / fixes should be produced for these types.
+void otherTestStringTests() {
+  other::TestString a = "";
+  other::TestString b("");
+  other::string c = "";
+  other::string d("");
+  other::wstring e = L"";
+  other::wstring f(L"");
+}