[NFC] Fix issues with -verify mode

This commit fixes two weird bugs in -verify mode:

1. SourceLocs from the wrong SourceManager could be passed through a ForwardingDiagnosticConsumer into the DiagnosticVerifier.

2. -verify-additional-file did not error out correctly when the file couldn’t be opened.

No tests, as we only have basic tests for the diagnostic verifier.

Author: beccadax

include/swift/Basic/SourceManager.h

@@ -290,6 +290,11 @@ class SourceManager {
   bool isLocInVirtualFile(SourceLoc Loc) const {
     return getVirtualFile(Loc) != nullptr;
   }
+
+  /// Return a SourceLoc in \c this corresponding to \p otherLoc, which must be
+  /// owned by \p otherManager. Returns an invalid SourceLoc if it cannot be
+  /// translated.
+  SourceLoc getLocForForeignLoc(SourceLoc otherLoc, SourceManager &otherMgr);
 };
 
 } // end namespace swift

lib/Basic/SourceLoc.cpp

@@ -395,3 +395,27 @@ SourceManager::getLocFromExternalSource(StringRef Path, unsigned Line,
     return SourceLoc();
   return getLocForOffset(BufferId, *Offset);
 }
+
+SourceLoc
+SourceManager::getLocForForeignLoc(SourceLoc otherLoc,
+                                   SourceManager &otherMgr) {
+  if (&otherMgr == this || otherLoc.isInvalid())
+    return otherLoc;
+
+  assert(otherMgr.isOwning(otherLoc));
+
+  if (auto otherBufferID = otherMgr.findBufferContainingLocInternal(otherLoc)) {
+    auto offset = otherMgr.getLocOffsetInBuffer(otherLoc, *otherBufferID);
+
+    auto otherBufferName = otherMgr.getIdentifierForBuffer(*otherBufferID);
+    auto thisBufferID = getIDForBufferIdentifier(otherBufferName);
+    if (!thisBufferID) {
+      thisBufferID = addMemBufferCopy(
+              otherMgr.getEntireTextForBuffer(*otherBufferID), otherBufferName);
+    }
+
+    return getLocForOffset(*thisBufferID, offset);
+  }
+
+  return SourceLoc();
+}

lib/Frontend/DiagnosticVerifier.cpp

@@ -972,6 +972,22 @@ void DiagnosticVerifier::handleDiagnostic(SourceManager &SM,
     CapturedDiagnostics.emplace_back(message, StringRef(), Info.Kind, Info.Loc,
                                      0, 0, fixIts, eduNotes);
   }
+
+  // If this diagnostic came from a different SourceManager (as can happen
+  // while compiling a module interface), translate its SourceLocs to match the
+  // verifier's SourceManager.
+  if (&SM != &(this->SM)) {
+    auto &capturedDiag = CapturedDiagnostics.back();
+    auto &correctSM = this->SM;
+
+    capturedDiag.Loc = correctSM.getLocForForeignLoc(capturedDiag.Loc, SM);
+    for (auto &fixIt : capturedDiag.FixIts) {
+      auto newStart = correctSM.getLocForForeignLoc(fixIt.getRange().getStart(),
+                                                    SM);
+      fixIt.getRange() = CharSourceRange(newStart,
+                                         fixIt.getRange().getByteLength());
+    }
+  }
 }
 
 /// Once all diagnostics have been captured, perform verification.

lib/Frontend/Frontend.cpp

@@ -307,6 +307,7 @@ bool CompilerInstance::setupDiagnosticVerifierIfNeeded() {
         Diagnostics.diagnose(SourceLoc(), diag::error_open_input_file,
                              filename, result.getError().message());
         hadError |= true;
+        continue;
       }
 
       auto bufferID = SourceMgr.addNewSourceBuffer(std::move(result.get()));