BitStream reader: propagate errors

The bitstream reader handles errors poorly. This has two effects:

 * Bugs in file handling (especially modules) manifest as an "unexpected end of
   file" crash
 * Users of clang as a library end up aborting because the code unconditionally
   calls `report_fatal_error`

The bitstream reader should be more resilient and return Expected / Error as
soon as an error is encountered, not way late like it does now. This patch
starts doing so and adopting the error handling where I think it makes sense.
There's plenty more to do: this patch propagates errors to be minimally useful,
and follow-ups will propagate them further and improve diagnostics.

https://bugs.llvm.org/show_bug.cgi?id=42311
<rdar://problem/33159405>

Differential Revision: https://reviews.llvm.org/D63518

llvm-svn: 364464

1 files changed, 3 insertions, 2 deletions

diff --git a/clang-tools-extra/clangd/CodeComplete.cpp b/clang-tools-extra/clangd/CodeComplete.cpp
index 208376a80cd..5bb24941c11 100644
--- a/clang-tools-extra/clangd/CodeComplete.cpp
+++ b/clang-tools-extra/clangd/CodeComplete.cpp
@@ -1105,8 +1105,9 @@ bool semaCodeComplete(std::unique_ptr<CodeCompleteConsumer> Consumer,
   if (Includes)
     Clang->getPreprocessor().addPPCallbacks(
         collectIncludeStructureCallback(Clang->getSourceManager(), Includes));
-  if (!Action.Execute()) {
-    log("Execute() failed when running codeComplete for {0}", Input.FileName);
+  if (llvm::Error Err = Action.Execute()) {
+    log("Execute() failed when running codeComplete for {0}: {1}",
+        Input.FileName, toString(std::move(Err)));
     return false;
   }
   Action.EndSourceFile();