[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

1 files changed, 9 insertions, 6 deletions

diff --git a/clang-tools-extra/unittests/clang-tidy/TransformerClangTidyCheckTest.cpp b/clang-tools-extra/unittests/clang-tidy/TransformerClangTidyCheckTest.cpp
index 1426dbbc09b..6b8763810e9 100644
--- a/clang-tools-extra/unittests/clang-tidy/TransformerClangTidyCheckTest.cpp
+++ b/clang-tools-extra/unittests/clang-tidy/TransformerClangTidyCheckTest.cpp
@@ -26,15 +26,18 @@ RewriteRule invertIf() {
   using tooling::change;
   using tooling::node;
   using tooling::statement;
+  using tooling::text;
   using tooling::stencil::cat;
 
   StringRef C = "C", T = "T", E = "E";
-  return tooling::makeRule(ifStmt(hasCondition(expr().bind(C)),
-                                  hasThen(stmt().bind(T)),
-                                  hasElse(stmt().bind(E))),
-                           change(statement(RewriteRule::RootID),
-                                  cat("if(!(", node(C), ")) ", statement(E),
-                                      " else ", statement(T))));
+  RewriteRule Rule = tooling::makeRule(
+      ifStmt(hasCondition(expr().bind(C)), hasThen(stmt().bind(T)),
+             hasElse(stmt().bind(E))),
+      change(
+          statement(RewriteRule::RootID),
+          cat("if(!(", node(C), ")) ", statement(E), " else ", statement(T))),
+      text("negate condition and reverse `then` and `else` branches"));
+  return Rule;
 }
 
 class IfInverterCheck : public TransformerClangTidyCheck {