Add modernize-use-default check to clang-tidy.

Summary:
Add a check that replaces empty bodies of special member functions with '= default;'.
For now, it is only implemented for the default constructor and the destructor, which are the easier cases.
The copy-constructor and the copy-assignment operator cases will be implemented later.

I applied this check to the llvm code base and found 627 warnings (385 in llvm, 9 in compiler-rt, 220 in clang and 13 in clang-tools-extra).
Applying the fixes didn't break any build or test, it only caused a -Wpedantic warning in lib/Target/Mips/MipsOptionRecord.h:33 becaused it replaced
virtual ~MipsOptionRecord(){}; to virtual ~MipsOptionRecord()= default;;

Reviewers: klimek

Subscribers: george.burgess.iv, Eugene.Zelenko, alexfh, cfe-commits

Differential Revision: http://reviews.llvm.org/D13871

llvm-svn: 250897

1 files changed, 63 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/modernize/UseDefaultCheck.cpp b/clang-tools-extra/clang-tidy/modernize/UseDefaultCheck.cpp
new file mode 100644
index 00000000000..829371b3e1e
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/modernize/UseDefaultCheck.cpp
@@ -0,0 +1,63 @@
+//===--- UseDefaultCheck.cpp - clang-tidy----------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "UseDefaultCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace modernize {
+
+static const char CtorDtor[] = "CtorDtorDecl";
+
+void UseDefaultCheck::registerMatchers(MatchFinder *Finder) {
+  if (getLangOpts().CPlusPlus) {
+    Finder->addMatcher(
+        cxxConstructorDecl(isDefinition(),
+                           unless(hasAnyConstructorInitializer(anything())),
+                           parameterCountIs(0))
+            .bind(CtorDtor),
+        this);
+    Finder->addMatcher(cxxDestructorDecl(isDefinition()).bind(CtorDtor), this);
+  }
+}
+
+void UseDefaultCheck::check(const MatchFinder::MatchResult &Result) {
+  // Both CXXConstructorDecl and CXXDestructorDecl inherit from CXXMethodDecl.
+  const auto *CtorDtorDecl = Result.Nodes.getNodeAs<CXXMethodDecl>(CtorDtor);
+
+  // Discard explicitly deleted/defaulted constructors/destructors, those that
+  // are not user-provided (automatically generated constructor/destructor), and
+  // those with non-empty bodies.
+  if (CtorDtorDecl->isDeleted() || CtorDtorDecl->isExplicitlyDefaulted() ||
+      !CtorDtorDecl->isUserProvided() || !CtorDtorDecl->hasTrivialBody())
+    return;
+
+  const auto *Body = dyn_cast<CompoundStmt>(CtorDtorDecl->getBody());
+  // This should never happen, since 'hasTrivialBody' checks that this is
+  // actually a CompoundStmt.
+  assert(Body && "Definition body is not a CompoundStmt");
+
+  diag(CtorDtorDecl->getLocStart(),
+       "use '= default' to define a trivial " +
+           std::string(dyn_cast<CXXConstructorDecl>(CtorDtorDecl)
+                           ? "default constructor"
+                           : "destructor"))
+      << FixItHint::CreateReplacement(
+          CharSourceRange::getTokenRange(Body->getLBracLoc(),
+                                         Body->getRBracLoc()),
+          "= default;");
+}
+
+} // namespace modernize
+} // namespace tidy
+} // namespace clang