[clang-tidy] Add check 'misc-string-compare'.

I have a created a new check for clang tidy: misc-string-compare. This will check for incorrect usage of std::string::compare when used to check equality or inequality of string instead of the string equality or inequality operators.

Example:
```
  std::string str1, str2;
  if (str1.compare(str2)) {
  }
```

Reviewers: hokein, aaron.ballman, alexfh, malcolm.parsons

Subscribers: xazax.hun, Eugene.Zelenko, cfe-commits, malcolm.parsons, Prazek, mgorny, JDevlieghere

Differential Revision: https://reviews.llvm.org/D27210

llvm-svn: 290747

1 files changed, 82 insertions, 0 deletions

diff --git a/clang-tools-extra/clang-tidy/misc/StringCompareCheck.cpp b/clang-tools-extra/clang-tidy/misc/StringCompareCheck.cpp
new file mode 100644
index 00000000000..b6a42953335
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/misc/StringCompareCheck.cpp
@@ -0,0 +1,82 @@
+//===--- MiscStringCompare.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 "StringCompareCheck.h"
+#include "../utils/FixItHintUtils.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+#include "clang/Tooling/FixIt.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace misc {
+
+static const StringRef CompareMessage = "do not use 'compare' to test equality "
+                                        "of strings; use the string equality "
+                                        "operator instead";
+
+void StringCompareCheck::registerMatchers(MatchFinder *Finder) {
+  if (!getLangOpts().CPlusPlus)
+    return;
+
+  const auto StrCompare = cxxMemberCallExpr(
+      callee(cxxMethodDecl(hasName("compare"),
+                           ofClass(classTemplateSpecializationDecl(
+                               hasName("::std::basic_string"))))),
+      hasArgument(0, expr().bind("str2")), argumentCountIs(1),
+      callee(memberExpr().bind("str1")));
+
+  // First and second case: cast str.compare(str) to boolean.
+  Finder->addMatcher(implicitCastExpr(hasImplicitDestinationType(booleanType()),
+                                      has(StrCompare))
+                         .bind("match1"),
+                     this);
+
+  // Third and fourth case: str.compare(str) == 0 and str.compare(str) != 0.
+  Finder->addMatcher(
+      binaryOperator(anyOf(hasOperatorName("=="), hasOperatorName("!=")),
+                     hasEitherOperand(StrCompare.bind("compare")),
+                     hasEitherOperand(integerLiteral(equals(0)).bind("zero")))
+          .bind("match2"),
+      this);
+}
+
+void StringCompareCheck::check(const MatchFinder::MatchResult &Result) {
+  if (const auto *Matched = Result.Nodes.getNodeAs<Stmt>("match1")) {
+    diag(Matched->getLocStart(), CompareMessage);
+    return;
+  }
+
+  if (const auto *Matched = Result.Nodes.getNodeAs<Stmt>("match2")) {
+    const ASTContext &Ctx = *Result.Context;
+
+    if (const auto *Zero = Result.Nodes.getNodeAs<Stmt>("zero")) {
+      const auto *Str1 = Result.Nodes.getNodeAs<MemberExpr>("str1");
+      const auto *Str2 = Result.Nodes.getNodeAs<Stmt>("str2");
+      const auto *Compare = Result.Nodes.getNodeAs<Stmt>("compare");
+
+      auto Diag = diag(Matched->getLocStart(), CompareMessage);
+
+      if (Str1->isArrow())
+        Diag << FixItHint::CreateInsertion(Str1->getLocStart(), "*");
+
+      Diag << tooling::fixit::createReplacement(*Zero, *Str2, Ctx)
+           << tooling::fixit::createReplacement(*Compare, *Str1->getBase(),
+                                                Ctx);
+    }
+  }
+
+  // FIXME: Add fixit to fix the code for case one and two (match1).
+}
+
+} // namespace misc
+} // namespace tidy
+} // namespace clang