1 files changed, 140 insertions, 0 deletions
diff --git a/clang-tools-extra/clang-tidy/abseil/RedundantStrcatCallsCheck.cpp b/clang-tools-extra/clang-tidy/abseil/RedundantStrcatCallsCheck.cpp
new file mode 100644
index 00000000000..19806685f89
--- /dev/null
+++ b/clang-tools-extra/clang-tidy/abseil/RedundantStrcatCallsCheck.cpp
@@ -0,0 +1,140 @@
+//===--- RedundantStrcatCallsCheck.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 "RedundantStrcatCallsCheck.h"
+#include "clang/AST/ASTContext.h"
+#include "clang/ASTMatchers/ASTMatchFinder.h"
+
+using namespace clang::ast_matchers;
+
+namespace clang {
+namespace tidy {
+namespace abseil {
+
+// TODO: Features to add to the check:
+//  - Make it work if num_args > 26.
+//  - Remove empty literal string arguments.
+//  - Collapse consecutive literal string arguments into one (remove the ,).
+//  - Replace StrCat(a + b)  ->  StrCat(a, b)  if a or b are strings.
+//  - Make it work in macros if the outer and inner StrCats are both in the
+//    argument.
+
+void RedundantStrcatCallsCheck::registerMatchers(MatchFinder* Finder) {
+  if (!getLangOpts().CPlusPlus) 
+  	return;
+  const auto CallToStrcat =
+      callExpr(callee(functionDecl(hasName("::absl::StrCat"))));
+  const auto CallToStrappend =
+      callExpr(callee(functionDecl(hasName("::absl::StrAppend"))));
+  // Do not match StrCat() calls that are descendants of other StrCat calls.
+  // Those are handled on the ancestor call.
+  const auto CallToEither = callExpr(
+      callee(functionDecl(hasAnyName("::absl::StrCat", "::absl::StrAppend"))));
+  Finder->addMatcher(
+      callExpr(CallToStrcat, unless(hasAncestor(CallToEither))).bind("StrCat"),
+      this);
+  Finder->addMatcher(CallToStrappend.bind("StrAppend"), this);
+}
+
+namespace {
+
+struct StrCatCheckResult {
+  int NumCalls = 0;
+  std::vector<FixItHint> Hints;
+};
+
+void RemoveCallLeaveArgs(const CallExpr* Call, StrCatCheckResult* CheckResult) {
+  // Remove 'Foo('
+  CheckResult->Hints.push_back(
+      FixItHint::CreateRemoval(CharSourceRange::getCharRange(
+          Call->getBeginLoc(), Call->getArg(0)->getBeginLoc())));
+  // Remove the ')'
+  CheckResult->Hints.push_back(
+      FixItHint::CreateRemoval(CharSourceRange::getCharRange(
+          Call->getRParenLoc(), Call->getEndLoc().getLocWithOffset(1))));
+}
+
+const clang::CallExpr* ProcessArgument(const Expr* Arg,
+                                       const MatchFinder::MatchResult& Result,
+                                       StrCatCheckResult* CheckResult) {
+  const auto IsAlphanum = hasDeclaration(cxxMethodDecl(hasName("AlphaNum")));
+  static const auto* const Strcat = new auto(hasName("::absl::StrCat"));
+  const auto IsStrcat = cxxBindTemporaryExpr(
+      has(callExpr(callee(functionDecl(*Strcat))).bind("StrCat")));
+  if (const auto* SubStrcatCall = selectFirst<const CallExpr>(
+          "StrCat",
+          match(stmt(anyOf(
+                    cxxConstructExpr(IsAlphanum, hasArgument(0, IsStrcat)),
+                    IsStrcat)),
+                *Arg->IgnoreParenImpCasts(), *Result.Context))) {
+    RemoveCallLeaveArgs(SubStrcatCall, CheckResult);
+    return SubStrcatCall;
+  }
+  return nullptr;
+}
+
+StrCatCheckResult ProcessCall(const CallExpr* RootCall, bool IsAppend,
+                              const MatchFinder::MatchResult& Result) {
+  StrCatCheckResult CheckResult;
+  std::deque<const CallExpr*> CallsToProcess = {RootCall};
+
+  while (!CallsToProcess.empty()) {
+    ++CheckResult.NumCalls;
+
+    const CallExpr* CallExpr = CallsToProcess.front();
+    CallsToProcess.pop_front();
+
+    int StartArg = CallExpr == RootCall && IsAppend;
+    for (const auto *Arg : CallExpr->arguments()) {
+      if (StartArg-- > 0) 
+      	continue;
+      if (const clang::CallExpr* Sub =
+              ProcessArgument(Arg, Result, &CheckResult)) {
+        CallsToProcess.push_back(Sub);
+      }
+    }
+  }
+  return CheckResult;
+}
+}  // namespace
+
+void RedundantStrcatCallsCheck::check(const MatchFinder::MatchResult& Result) {
+  bool IsAppend;
+
+  const CallExpr* RootCall;
+  if ((RootCall = Result.Nodes.getNodeAs<CallExpr>("StrCat"))) 
+  	IsAppend = false;
+  else if ((RootCall = Result.Nodes.getNodeAs<CallExpr>("StrAppend"))) 
+  	IsAppend = true;
+  else 
+  	return;
+
+  if (RootCall->getBeginLoc().isMacroID()) {
+    // Ignore calls within macros.
+    // In many cases the outer StrCat part of the macro and the inner StrCat is
+    // a macro argument. Removing the inner StrCat() converts one macro
+    // argument into many.
+    return;
+  }
+
+  const StrCatCheckResult CheckResult =
+      ProcessCall(RootCall, IsAppend, Result);
+  if (CheckResult.NumCalls == 1) {
+    // Just one call, so nothing to fix.
+    return;
+  }
+
+  diag(RootCall->getBeginLoc(), 
+  	   "multiple calls to 'absl::StrCat' can be flattened into a single call")
+      << CheckResult.Hints;
+}
+
+}  // namespace abseil
+}  // namespace tidy
+}  // namespace clang