Index: clang-tools-extra/trunk/clangd/Diagnostics.cpp
===================================================================
--- clang-tools-extra/trunk/clangd/Diagnostics.cpp
+++ clang-tools-extra/trunk/clangd/Diagnostics.cpp
@@ -297,7 +297,7 @@
     return D;
   };
 
-  auto AddFix = [&]() -> bool {
+  auto AddFix = [&](bool SyntheticMessage) -> bool {
     assert(!Info.getFixItHints().empty() &&
            "diagnostic does not have attached fix-its");
     if (!InsideMainFile)
@@ -312,7 +312,27 @@
     }
 
     llvm::SmallString<64> Message;
-    Info.FormatDiagnostic(Message);
+    // If requested and possible, create a message like "change 'foo' to 'bar'".
+    if (SyntheticMessage && Info.getNumFixItHints() == 1) {
+      const auto &FixIt = Info.getFixItHint(0);
+      bool Invalid = false;
+      StringRef Remove = Lexer::getSourceText(
+          FixIt.RemoveRange, Info.getSourceManager(), *LangOpts, &Invalid);
+      StringRef Insert = FixIt.CodeToInsert;
+      if (!Invalid) {
+        llvm::raw_svector_ostream M(Message);
+        if (!Remove.empty() && !Insert.empty())
+          M << "change '" << Remove << "' to '" << Insert << "'";
+        else if (!Remove.empty())
+          M << "remove '" << Remove << "'";
+        else if (!Insert.empty())
+          M << "insert '" << Insert << "'";
+        // Don't allow source code to inject newlines into diagnostics.
+        std::replace(Message.begin(), Message.end(), '\n', ' ');
+      }
+    }
+    if (Message.empty()) // either !SytheticMessage, or we failed to make one.
+      Info.FormatDiagnostic(Message);
     LastDiag->Fixes.push_back(Fix{Message.str(), std::move(Edits)});
     return true;
   };
@@ -325,7 +345,7 @@
     FillDiagBase(*LastDiag);
 
     if (!Info.getFixItHints().empty())
-      AddFix();
+      AddFix(true /* try to invent a message instead of repeating the diag */);
   } else {
     // Handle a note to an existing diagnostic.
     if (!LastDiag) {
@@ -337,7 +357,7 @@
     if (!Info.getFixItHints().empty()) {
       // A clang note with fix-it is not a separate diagnostic in clangd. We
       // attach it as a Fix to the main diagnostic instead.
-      if (!AddFix())
+      if (!AddFix(false /* use the note as the message */))
         IgnoreDiagnostics::log(DiagLevel, Info);
     } else {
       // A clang note without fix-its corresponds to clangd::Note.
Index: clang-tools-extra/trunk/unittests/clangd/ClangdUnitTests.cpp
===================================================================
--- clang-tools-extra/trunk/unittests/clangd/ClangdUnitTests.cpp
+++ clang-tools-extra/trunk/unittests/clangd/ClangdUnitTests.cpp
@@ -92,14 +92,6 @@
   return Res;
 }
 
-/// Matches diagnostic that has exactly one fix with the same range and message
-/// as the diagnostic itself.
-testing::Matcher<const clangd::Diag &> DiagWithEqualFix(clangd::Range Range,
-                                                        std::string Replacement,
-                                                        std::string Message) {
-  return AllOf(Diag(Range, Message), WithFix(Fix(Range, Replacement, Message)));
-}
-
 TEST(DiagnosticsTest, DiagnosticRanges) {
   // Check we report correct ranges, including various edge-cases.
   Annotations Test(R"cpp(
@@ -111,19 +103,19 @@
       $unk[[unknown]]();
     }
   )cpp");
-  llvm::errs() << Test.code();
   EXPECT_THAT(
       buildDiags(Test.code()),
       ElementsAre(
           // This range spans lines.
-          AllOf(DiagWithEqualFix(
-                    Test.range("typo"), "foo",
-                    "use of undeclared identifier 'goo'; did you mean 'foo'?"),
+          AllOf(Diag(Test.range("typo"),
+                     "use of undeclared identifier 'goo'; did you mean 'foo'?"),
+                WithFix(
+                    Fix(Test.range("typo"), "foo", "change 'go\\ o' to 'foo'")),
                 // This is a pretty normal range.
                 WithNote(Diag(Test.range("decl"), "'foo' declared here"))),
           // This range is zero-width, and at the end of a line.
-          DiagWithEqualFix(Test.range("semicolon"), ";",
-                           "expected ';' after expression"),
+          AllOf(Diag(Test.range("semicolon"), "expected ';' after expression"),
+                WithFix(Fix(Test.range("semicolon"), ";", "insert ';'"))),
           // This range isn't provided by clang, we expand to the token.
           Diag(Test.range("unk"), "use of undeclared identifier 'unknown'")));
 }
@@ -131,8 +123,9 @@
 TEST(DiagnosticsTest, FlagsMatter) {
   Annotations Test("[[void]] main() {}");
   EXPECT_THAT(buildDiags(Test.code()),
-              ElementsAre(DiagWithEqualFix(Test.range(), "int",
-                                           "'main' must return 'int'")));
+              ElementsAre(AllOf(Diag(Test.range(), "'main' must return 'int'"),
+                                WithFix(Fix(Test.range(), "int",
+                                            "change 'void' to 'int'")))));
   // Same code built as C gets different diagnostics.
   EXPECT_THAT(
       buildDiags(Test.code(), {"-x", "c"}),