[Caching] Improve diagnostics around swift caching

Improve diagnostics message for swift caching build by trying to emit
the diagnostics early when there is more context to differentiate the
different kind of problems.

After the improvement, CAS Error should be more closer to when there is
functional problem with the CAS, rather than mixing in other kinds of
problem (like scanning dependency failures) when operating with a CAS.

rdar://145676736

Author: cachemeifyoucan

include/swift/AST/DiagnosticsFrontend.def

@@ -525,7 +525,12 @@ REMARK(replay_output, none, "replay output file '%0': key '%1'", (StringRef, Str
 REMARK(output_cache_miss, none, "cache miss for input file '%0': key '%1'", (StringRef, StringRef))
 
 // CAS related diagnostics
-ERROR(error_cas, none, "CAS error encountered: %0", (StringRef))
+ERROR(error_invalid_cas_id, none, "cannot parse CASID '%0': %1", (StringRef, StringRef))
+ERROR(error_cas, none, "CAS error encountered during %0: %1", (StringRef, StringRef))
+ERROR(error_cas_fs_creation, none, "cannot create CAS file system: %0", (StringRef))
+ERROR(error_cache_key_creation, none, "cannot create cache key for compilation %0: %1", (StringRef, StringRef))
+ERROR(error_cas_file_ref, none, "failed to get CAS ref for file: %0", (StringRef))
+ERROR(error_cas_setup, none, "CAS setup error: %0", (StringRef))
 WARNING(cache_replay_failed, none, "cache replay failed: %0", (StringRef))
 
 ERROR(error_failed_cached_diag, none, "failed to serialize cached diagnostics: %0", (StringRef))

lib/AST/ModuleDependencies.cpp

@@ -680,8 +680,11 @@ SwiftDependencyTracker::createTreeFromDependencies() {
   for (auto &file : TrackedFiles) {
     auto includeTreeFile = clang::cas::IncludeTree::File::create(
         FS->getCAS(), file.first, file.second.FileRef);
-    if (!includeTreeFile)
-      return includeTreeFile.takeError();
+    if (!includeTreeFile) {
+      return llvm::createStringError("CASFS createTree failed for " +
+                                     file.first + ": " +
+                                     toString(includeTreeFile.takeError()));
+    }
     Files.push_back(
         {includeTreeFile->getRef(),
          (clang::cas::IncludeTree::FileList::FileSizeTy)file.second.Size});
@@ -690,7 +693,8 @@ SwiftDependencyTracker::createTreeFromDependencies() {
   auto includeTreeList =
       clang::cas::IncludeTree::FileList::create(FS->getCAS(), Files, {});
   if (!includeTreeList)
-    return includeTreeList.takeError();
+    return llvm::createStringError("casfs include-tree filelist error: " +
+                                   toString(includeTreeList.takeError()));
 
   return *includeTreeList;
 }
@@ -707,7 +711,7 @@ bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
 
     // CASOption mismatch, return error.
     Instance.getDiags().diagnose(
-        SourceLoc(), diag::error_cas,
+        SourceLoc(), diag::error_cas_setup,
         "conflicting CAS options used in scanning service");
     return true;
   }
@@ -720,7 +724,7 @@ bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
   auto CachingFS =
       llvm::cas::createCachingOnDiskFileSystem(Instance.getObjectStore());
   if (!CachingFS) {
-    Instance.getDiags().diagnose(SourceLoc(), diag::error_cas,
+    Instance.getDiags().diagnose(SourceLoc(), diag::error_cas_setup,
                                  toString(CachingFS.takeError()));
     return true;
   }