[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 +525,13 @@ 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, "CAS cannot parse id '%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 filesystem: %0", (StringRef))
+ERROR(error_cache_key_creation, none, "cannot create cache key for compilation %0: %1", (StringRef, StringRef))
+ERROR(error_cas_file_ref, none, "cannot load file %0 from CAS filesystem", (StringRef))
+ERROR(error_cas_conflict_options, none, "cannot setup CAS due to conflicting '-cas-*' options", ())
+ERROR(error_cas_initialization, none, "CAS cannot be initialized from the specified '-cas-*' options: %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;
 }
@@ -706,9 +710,7 @@ bool SwiftDependencyScanningService::setupCachingDependencyScanningService(
       return false;
 
     // CASOption mismatch, return error.
-    Instance.getDiags().diagnose(
-        SourceLoc(), diag::error_cas,
-        "conflicting CAS options used in scanning service");
+    Instance.getDiags().diagnose(SourceLoc(), diag::error_cas_conflict_options);
     return true;
   }
 
@@ -720,7 +722,7 @@ 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_fs_creation,
                                  toString(CachingFS.takeError()));
     return true;
   }