gopls/internal/lsp/source: address problems detected by staticcheck

While working on performance I disabled staticcheck. Reenabling it
today turned up several suggestions, and a few real bugs.

Change-Id: I032d0cfb12ec8fda2573a2663faec4126b321afc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/557496
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

gopls/internal/lsp/source/change_signature.go

@@ -134,6 +134,7 @@ func RemoveUnusedParameter(ctx context.Context, fh file.Handle, rng protocol.Ran
 	if err != nil {
 		return nil, err
 	}
+
 	// Finally, rewrite the original declaration. We do this after inlining all
 	// calls, as there may be calls in the same file as the declaration. But none
 	// of the inlining should have changed the location of the original
@@ -149,7 +150,10 @@ func RemoveUnusedParameter(ctx context.Context, fh file.Handle, rng protocol.Ran
 			src = pgf.Src
 		}
 		fset := tokeninternal.FileSetFor(pgf.Tok)
-		src, err = rewriteSignature(fset, idx, src, newDecl)
+		src, err := rewriteSignature(fset, idx, src, newDecl)
+		if err != nil {
+			return nil, err
+		}
 		newContent[pgf.URI] = src
 	}
 

gopls/internal/lsp/source/codeaction.go

@@ -98,7 +98,7 @@ func CodeActions(ctx context.Context, snapshot *cache.Snapshot, fh file.Handle,
 			return nil, err
 		}
 		if want[protocol.RefactorRewrite] {
-			rewrites, err := getRewriteCodeActions(snapshot, pkg, pgf, fh, rng, snapshot.Options())
+			rewrites, err := getRewriteCodeActions(pkg, pgf, fh, rng, snapshot.Options())
 			if err != nil {
 				return nil, err
 			}
@@ -253,7 +253,7 @@ func newCodeAction(title string, kind protocol.CodeActionKind, cmd *protocol.Com
 }
 
 // getRewriteCodeActions returns refactor.rewrite code actions available at the specified range.
-func getRewriteCodeActions(snapshot *cache.Snapshot, pkg *cache.Package, pgf *ParsedGoFile, fh file.Handle, rng protocol.Range, options *settings.Options) (_ []protocol.CodeAction, rerr error) {
+func getRewriteCodeActions(pkg *cache.Package, pgf *ParsedGoFile, fh file.Handle, rng protocol.Range, options *settings.Options) (_ []protocol.CodeAction, rerr error) {
 	// golang/go#61693: code actions were refactored to run outside of the
 	// analysis framework, but as a result they lost their panic recovery.
 	//

gopls/internal/lsp/source/definition.go

@@ -150,8 +150,10 @@ func builtinDecl(ctx context.Context, snapshot *cache.Snapshot, obj types.Object
 		if err != nil {
 			return nil, nil, err
 		}
-
 		decl, err = getDecl(pgf.File, obj.Name())
+		if err != nil {
+			return nil, nil, err
+		}
 	} else {
 		// pseudo-package "builtin":
 		// use parsed $GOROOT/src/builtin/builtin.go
@@ -163,7 +165,9 @@ func builtinDecl(ctx context.Context, snapshot *cache.Snapshot, obj types.Object
 		if obj.Parent() == types.Universe {
 			// built-in function or type
 			decl, err = getDecl(pgf.File, obj.Name())
-
+			if err != nil {
+				return nil, nil, err
+			}
 		} else if obj.Name() == "Error" {
 			// error.Error method
 			decl, err = getDecl(pgf.File, "error")

gopls/internal/lsp/source/invertifcondition.go

@@ -92,7 +92,7 @@ func invertIfCondition(fset *token.FileSet, start, end token.Pos, src []byte, fi
 func endsWithReturn(elseBranch ast.Stmt) (bool, error) {
 	elseBlock, isBlockStatement := elseBranch.(*ast.BlockStmt)
 	if !isBlockStatement {
-		return false, fmt.Errorf("Unable to figure out whether this ends with return: %T", elseBranch)
+		return false, fmt.Errorf("unable to figure out whether this ends with return: %T", elseBranch)
 	}
 
 	if len(elseBlock.List) == 0 {

gopls/internal/lsp/source/rename.go

@@ -402,7 +402,7 @@ func renameOrdinary(ctx context.Context, snapshot *cache.Snapshot, f file.Handle
 	// transitive rdeps. (The exportedness of the field's struct
 	// or method's receiver is irrelevant.)
 	transitive := false
-	switch obj.(type) {
+	switch obj := obj.(type) {
 	case *types.TypeName:
 		// Renaming an exported package-level type
 		// requires us to inspect all transitive rdeps
@@ -418,7 +418,7 @@ func renameOrdinary(ctx context.Context, snapshot *cache.Snapshot, f file.Handle
 		}
 
 	case *types.Var:
-		if obj.(*types.Var).IsField() {
+		if obj.IsField() {
 			transitive = true // field
 		}