internal/lsp: return context cancellation from LookupBuiltin

Change-Id: If90d111fbe89d2be445b15ec3721d48280540de9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/216305
Run-TryBot: Rebecca Stambler <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Heschi Kreinick <[email protected]>

Author: stamblerre

internal/lsp/cache/view.go

@@ -204,6 +204,9 @@ func (v *view) LookupBuiltin(ctx context.Context, name string) (*ast.Object, err
 		return nil, err
 	}
 	data := v.builtin.handle.Get(ctx)
+	if ctx.Err() != nil {
+		return nil, ctx.Err()
+	}
 	if data == nil {
 		return nil, errors.Errorf("unexpected nil builtin package")
 	}

internal/lsp/source/completion_format.go

@@ -246,7 +246,9 @@ func (c *completer) formatBuiltin(cand candidate) CompletionItem {
 		item.Kind = protocol.FunctionCompletion
 		astObj, err := c.snapshot.View().LookupBuiltin(c.ctx, obj.Name())
 		if err != nil {
-			log.Error(c.ctx, "no builtin package", err)
+			if c.ctx.Err() == nil {
+				log.Error(c.ctx, "no builtin package", err)
+			}
 			break
 		}
 		decl, ok := astObj.Decl.(*ast.FuncDecl)