[clang-tidy] Fix readability-redundant-string-init for c++17/c++2a

Summary:
`readability-redundant-string-init` was one of several clang-tidy checks documented as failing for C++17. (The failure mode in C++17 is that it changes `std::string Name = ""`; to `std::string Name = Name;`, which actually compiles but crashes at run-time.)

Analyzing the AST with `clang -Xclang -ast-dump` showed that the outer `CXXConstructExprs` that previously held the correct SourceRange were being elided in C++17/2a, but the containing `VarDecl` expressions still had all the relevant information. So this patch changes the fix to get its source ranges from `VarDecl`.

It adds one test `std::string g = "u", h = "", i = "uuu", j = "", k;` to confirm proper warnings and fixit replacements in a single `DeclStmt` where some strings require replacement and others don't. The readability-redundant-string-init.cpp and readability-redundant-string-init-msvc.cpp tests now pass for C++11/14/17/2a.

Reviewers: gribozavr, etienneb, alexfh, hokein, aaron.ballman, gribozavr2

Patch by: poelmanc

Subscribers: NoQ, MyDeveloperDay, Eugene.Zelenko, dylanmckay, cfe-commits

Tags: #clang, #clang-tools-extra

Differential Revision: https://reviews.llvm.org/D69238

1 files changed, 7 insertions, 6 deletions

diff --git a/clang-tools-extra/clang-tidy/readability/RedundantStringInitCheck.cpp b/clang-tools-extra/clang-tidy/readability/RedundantStringInitCheck.cpp
index 42f802cd0af..6bf0edb7231 100644
--- a/clang-tools-extra/clang-tidy/readability/RedundantStringInitCheck.cpp
+++ b/clang-tools-extra/clang-tidy/readability/RedundantStringInitCheck.cpp
@@ -73,7 +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"),
@@ -82,11 +82,12 @@ void RedundantStringInitCheck::registerMatchers(MatchFinder *Finder) {
 }
 
 void RedundantStringInitCheck::check(const MatchFinder::MatchResult &Result) {
-  const auto *CtorExpr = Result.Nodes.getNodeAs<Expr>("expr");
-  const auto *Decl = Result.Nodes.getNodeAs<NamedDecl>("decl");
-  diag(CtorExpr->getExprLoc(), "redundant string initialization")
-      << FixItHint::CreateReplacement(CtorExpr->getSourceRange(),
-                                      Decl->getName());
+  const auto *VDecl = Result.Nodes.getNodeAs<VarDecl>("vardecl");
+  // VarDecl's getSourceRange() spans 'string foo = ""' or 'string bar("")'.
+  // So start at getLocation() to span just 'foo = ""' or 'bar("")'.
+  SourceRange ReplaceRange(VDecl->getLocation(), VDecl->getEndLoc());
+  diag(VDecl->getLocation(), "redundant string initialization")
+      << FixItHint::CreateReplacement(ReplaceRange, VDecl->getName());
 }
 
 } // namespace readability