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, 5 insertions, 1 deletions

diff --git a/clang/lib/Frontend/Rewrite/FrontendActions.cpp b/clang/lib/Frontend/Rewrite/FrontendActions.cpp
index aaef44b79dc..0f1a0584c72 100644
--- a/clang/lib/Frontend/Rewrite/FrontendActions.cpp
+++ b/clang/lib/Frontend/Rewrite/FrontendActions.cpp
@@ -129,7 +129,11 @@ bool FixItRecompile::BeginInvocation(CompilerInstance &CI) {
       FixItOpts->FixOnlyWarnings = FEOpts.FixOnlyWarnings;
       FixItRewriter Rewriter(CI.getDiagnostics(), CI.getSourceManager(),
                              CI.getLangOpts(), FixItOpts.get());
-      FixAction->Execute();
+      if (llvm::Error Err = FixAction->Execute()) {
+        // FIXME this drops the error on the floor.
+        consumeError(std::move(Err));
+        return false;
+      }
 
       err = Rewriter.WriteFixedFiles(&RewrittenFiles);