Ask user for relevant diagnostics when clang translation unit creation fails.

Closes issue #450.

src/clang_translation_unit.cc

@@ -93,24 +93,26 @@ std::unique_ptr<ClangTranslationUnit> ClangTranslationUnit::Create(
   if (error_code != CXError_Success && cx_tu)
     EmitDiagnostics(filepath, args, cx_tu);
 
+  auto make_msg = [&]() {
+    return "Please try running the following, identify which flag causes the "
+           "issue, and report a bug. cquery will then filter the flag for you "
+           " automatically:\n$ " + StringJoin(args, " ");
+  };
+
   switch (error_code) {
     case CXError_Success:
       return MakeUnique<ClangTranslationUnit>(cx_tu);
     case CXError_Failure:
-      LOG_S(ERROR) << "libclang generic failure for " << filepath
+      LOG_S(ERROR) << "libclang generic failure for " << filepath << ". " << make_msg();
-                   << " with args " << StringJoin(args);
       return nullptr;
     case CXError_Crashed:
-      LOG_S(ERROR) << "libclang crashed for " << filepath << " with args "
+      LOG_S(ERROR) << "libclang crashed for " << filepath << ". " << make_msg();
-                   << StringJoin(args);
       return nullptr;
     case CXError_InvalidArguments:
-      LOG_S(ERROR) << "libclang had invalid arguments for "
+      LOG_S(ERROR) << "libclang had invalid arguments for " << filepath << ". " << make_msg();
-                   << " with args " << StringJoin(args) << filepath;
       return nullptr;
     case CXError_ASTReadError:
-      LOG_S(ERROR) << "libclang had ast read error for " << filepath
+      LOG_S(ERROR) << "libclang had ast read error for " << filepath << ". " << make_msg();
-                   << " with args " << StringJoin(args);
       return nullptr;
   }
 

src/project.cc

@@ -265,7 +265,12 @@ Project::Entry GetCompilationEntryFromCompileCommandEntry(
   if (!AnyStartsWith(result.args, "-Wno-unknown-warning-option"))
     result.args.push_back("-Wno-unknown-warning-option");
 
-  // Using -fparse-all-comments enables documententation in the indexer and in
+  // We sometimes dump the command to logs and ask the user to run it. Include
+  // -fsyntax-only so they don't do a full compile.
+  if (!AnyStartsWith(result.args, "-fsyntax-only"))
+    result.args.push_back("-fsyntax-only");
+
+  // Using -fparse-all-comments enables documentation in the indexer and in
   // code completion.
   if (init_opts->index.comments > 1 &&
       !AnyStartsWith(result.args, "-fparse-all-comments")) {
@@ -598,28 +603,28 @@ TEST_SUITE("Project") {
         /* expected */
         {"clang", "-working-directory", "/dir/", "-xc++", "-std=c++14",
          "-lstdc++", "&/dir/myfile.cc", "-resource-dir=/w/resource_dir/",
-         "-Wno-unknown-warning-option", "-fparse-all-comments"});
+         "-Wno-unknown-warning-option", "-fsyntax-only", "-fparse-all-comments"});
 
     CheckFlags(
         /* raw */ {"clang.exe"},
         /* expected */
         {"clang.exe", "-working-directory", "/dir/", "-xc++", "-std=c++14",
          "-resource-dir=/w/resource_dir/", "-Wno-unknown-warning-option",
-         "-fparse-all-comments"});
+          "-fsyntax-only", "-fparse-all-comments"});
 
     CheckFlags(
         /* raw */ {"goma", "clang"},
         /* expected */
         {"clang", "-working-directory", "/dir/", "-xc++", "-std=c++14",
          "-resource-dir=/w/resource_dir/", "-Wno-unknown-warning-option",
-         "-fparse-all-comments"});
+         "-fsyntax-only", "-fparse-all-comments"});
 
     CheckFlags(
         /* raw */ {"goma", "clang", "--foo"},
         /* expected */
         {"clang", "-working-directory", "/dir/", "-xc++", "-std=c++14", "--foo",
          "-resource-dir=/w/resource_dir/", "-Wno-unknown-warning-option",
-         "-fparse-all-comments"});
+         "-fsyntax-only", "-fparse-all-comments"});
   }
 
   TEST_CASE("Windows path normalization") {
@@ -628,7 +633,7 @@ TEST_SUITE("Project") {
         /* expected */
         {"clang", "-working-directory", "E:/workdir", "-xc++", "-std=c++14",
          "&E:/workdir/bar.cc", "-resource-dir=/w/resource_dir/",
-         "-Wno-unknown-warning-option", "-fparse-all-comments"});
+         "-Wno-unknown-warning-option", "-fsyntax-only", "-fparse-all-comments"});
 
     CheckFlags(
         "E:/workdir", "E:/workdir/bar.cc",
@@ -636,7 +641,7 @@ TEST_SUITE("Project") {
         /* expected */
         {"clang", "-working-directory", "E:/workdir", "-xc++", "-std=c++14",
          "&E:/workdir/bar.cc", "-resource-dir=/w/resource_dir/",
-         "-Wno-unknown-warning-option", "-fparse-all-comments"});
+         "-Wno-unknown-warning-option", "-fsyntax-only", "-fparse-all-comments"});
   }
 
   TEST_CASE("Path in args") {
@@ -646,7 +651,7 @@ TEST_SUITE("Project") {
         /* expected */
         {"cc", "-working-directory", "/home/user", "-xc", "-std=gnu11", "-O0",
          "&/home/user/foo/bar.c", "-resource-dir=/w/resource_dir/",
-         "-Wno-unknown-warning-option", "-fparse-all-comments"});
+         "-Wno-unknown-warning-option", "-fsyntax-only", "-fparse-all-comments"});
   }
 
   TEST_CASE("Implied binary") {
@@ -656,7 +661,7 @@ TEST_SUITE("Project") {
         /* expected */
         {"clang++", "-working-directory", "/home/user", "-xc++", "-std=c++14",
          "-DDONT_IGNORE_ME", "-resource-dir=/w/resource_dir/",
-         "-Wno-unknown-warning-option", "-fparse-all-comments"});
+         "-Wno-unknown-warning-option", "-fsyntax-only", "-fparse-all-comments"});
   }
 
   // Checks flag parsing for a random chromium file in comparison to what
@@ -1007,6 +1012,7 @@ TEST_SUITE("Project") {
          "lock_screen_sanity_unittest.cc",
          "-resource-dir=/w/resource_dir/",
          "-Wno-unknown-warning-option",
+         "-fsyntax-only",
          "-fparse-all-comments"});
   }
 
@@ -1332,6 +1338,7 @@ TEST_SUITE("Project") {
          "&/w/c/s/out/Release/../../apps/app_lifetime_monitor.cc",
          "-resource-dir=/w/resource_dir/",
          "-Wno-unknown-warning-option",
+         "-fsyntax-only",
          "-fparse-all-comments"});
   }