Teach the related-id checker to ignore things from other buffers

lib/AST/Decl.cpp

@@ -422,7 +422,15 @@ unsigned Decl::getAttachedMacroDiscriminator(
         foundDiscriminator = discriminator;
     });
 
+  if (foundDiscriminator)
     return *foundDiscriminator;
+
+  // If that failed, conjure up a discriminator.
+  ASTContext &ctx = getASTContext();
+  assert(ctx.Diags.hadAnyError());
+  return ctx.getNextMacroDiscriminator(
+      MacroDiscriminatorContext::getParentOf(getLoc(), getDeclContext()),
+      DeclBaseName());
 }
 
 const Decl *Decl::getInnermostDeclWithAvailability() const {

tools/SourceKit/lib/SwiftLang/SwiftSourceDocInfo.cpp

@@ -2398,6 +2398,10 @@ private:
   }
 
   bool passId(CharSourceRange Range) {
+    // FIXME: Ignore things that don't come from this buffer.
+    if (!SourceMgr.getRangeForBuffer(BufferID).contains(Range.getStart()))
+      return !Cancelled;
+
     unsigned Offset = SourceMgr.getLocOffsetInBuffer(Range.getStart(),BufferID);
     Ranges.insert({Offset, Range.getByteLength()});
     return !Cancelled;