[clang-tidy] In TransformerClangTidyCheck, require Explanation field.

Summary:
In general, the `Explanation` field is optional in `RewriteRule` cases. But,
because the primary purpose of clang-tidy checks is to provide users with
diagnostics, we assume that a missing explanation is a bug.  This change adds an
assertion that checks all cases for an explanation, and updates the code to rely
on that assertion correspondingly.

Reviewers: ilya-biryukov

Subscribers: xazax.hun, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D62340

llvm-svn: 361647

2 files changed, 24 insertions, 11 deletions

diff --git a/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.cpp b/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.cpp
index f142de46441..12be8a6dce7 100644
--- a/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.cpp
+++ b/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.cpp
@@ -13,6 +13,17 @@ namespace tidy {
 namespace utils {
 using tooling::RewriteRule;
 
+TransformerClangTidyCheck::TransformerClangTidyCheck(tooling::RewriteRule R,
+                                                     StringRef Name,
+                                                     ClangTidyContext *Context)
+    : ClangTidyCheck(Name, Context), Rule(std::move(R)) {
+  for (const auto &Case : Rule.Cases) {
+    assert(Case.Explanation != nullptr &&
+           "clang-tidy checks must have an explanation by default;"
+           " explicitly provide an empty explanation if none is desired");
+  }
+}
+
 void TransformerClangTidyCheck::registerMatchers(
     ast_matchers::MatchFinder *Finder) {
   Finder->addDynamicMatcher(tooling::detail::buildMatcher(Rule), this);
@@ -44,15 +55,13 @@ void TransformerClangTidyCheck::check(
   if (Transformations->empty())
     return;
 
-  StringRef Message = "no explanation";
-  if (Case.Explanation) {
-    if (Expected<std::string> E = Case.Explanation(Result))
-      Message = *E;
-    else
-      llvm::errs() << "Error in explanation: " << llvm::toString(E.takeError())
-                   << "\n";
+  Expected<std::string> Explanation = Case.Explanation(Result);
+  if (!Explanation) {
+    llvm::errs() << "Error in explanation: "
+                 << llvm::toString(Explanation.takeError()) << "\n";
+    return;
   }
-  DiagnosticBuilder Diag = diag(RootLoc, Message);
+  DiagnosticBuilder Diag = diag(RootLoc, *Explanation);
   for (const auto &T : *Transformations) {
     Diag << FixItHint::CreateReplacement(T.Range, T.Replacement);
   }
diff --git a/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.h b/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.h
index 6d0f86795bf..faf946ceb0f 100644
--- a/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.h
+++ b/clang-tools-extra/clang-tidy/utils/TransformerClangTidyCheck.h
@@ -31,10 +31,14 @@ namespace utils {
 // };
 class TransformerClangTidyCheck : public ClangTidyCheck {
 public:
+  // All cases in \p R must have a non-null \c Explanation, even though \c
+  // Explanation is optional for RewriteRule in general. Because the primary
+  // purpose of clang-tidy checks is to provide users with diagnostics, we
+  // assume that a missing explanation is a bug.  If no explanation is desired,
+  // indicate that explicitly (for example, by passing `text("no explanation")`
+  //  to `makeRule` as the `Explanation` argument).
   TransformerClangTidyCheck(tooling::RewriteRule R, StringRef Name,
-                            ClangTidyContext *Context)
-      : ClangTidyCheck(Name, Context), Rule(std::move(R)) {}
-
+                            ClangTidyContext *Context);
   void registerMatchers(ast_matchers::MatchFinder *Finder) final;
   void check(const ast_matchers::MatchFinder::MatchResult &Result) final;