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, 20 insertions, 7 deletions

diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 9cbc9ed1f79..cf0267549e7 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -941,7 +941,9 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
       getSourceManager().clearIDTables();
 
     if (Act.BeginSourceFile(*this, FIF)) {
-      Act.Execute();
+      if (llvm::Error Err = Act.Execute()) {
+        consumeError(std::move(Err)); // FIXME this drops errors on the floor.
+      }
       Act.EndSourceFile();
     }
   }
@@ -2043,9 +2045,16 @@ GlobalModuleIndex *CompilerInstance::loadGlobalModuleIndex(
       hasPreprocessor()) {
     llvm::sys::fs::create_directories(
       getPreprocessor().getHeaderSearchInfo().getModuleCachePath());
-    GlobalModuleIndex::writeIndex(
-        getFileManager(), getPCHContainerReader(),
-        getPreprocessor().getHeaderSearchInfo().getModuleCachePath());
+    if (llvm::Error Err = GlobalModuleIndex::writeIndex(
+            getFileManager(), getPCHContainerReader(),
+            getPreprocessor().getHeaderSearchInfo().getModuleCachePath())) {
+      // FIXME this drops the error on the floor. This code is only used for
+      // typo correction and drops more than just this one source of errors
+      // (such as the directory creation failure above). It should handle the
+      // error.
+      consumeError(std::move(Err));
+      return nullptr;
+    }
     ModuleManager->resetForReload();
     ModuleManager->loadGlobalIndex();
     GlobalIndex = ModuleManager->getGlobalIndex();
@@ -2070,9 +2079,13 @@ GlobalModuleIndex *CompilerInstance::loadGlobalModuleIndex(
       }
     }
     if (RecreateIndex) {
-      GlobalModuleIndex::writeIndex(
-          getFileManager(), getPCHContainerReader(),
-          getPreprocessor().getHeaderSearchInfo().getModuleCachePath());
+      if (llvm::Error Err = GlobalModuleIndex::writeIndex(
+              getFileManager(), getPCHContainerReader(),
+              getPreprocessor().getHeaderSearchInfo().getModuleCachePath())) {
+        // FIXME As above, this drops the error on the floor.
+        consumeError(std::move(Err));
+        return nullptr;
+      }
       ModuleManager->resetForReload();
       ModuleManager->loadGlobalIndex();
       GlobalIndex = ModuleManager->getGlobalIndex();