gopls/internal/golang: don't offer to move variadic parameters

While we can't handle moving variadic parameters, don't offer to move
them.

For golang/go#70599

Change-Id: I21e78b4e2ae8c061d3858f2f981d593a6b0cf5bc
Reviewed-on: https://go-review.googlesource.com/c/tools/+/633096
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Findley <rfindley@google.com>

Author: findleyr

gopls/internal/golang/codeaction.go

@@ -548,7 +548,12 @@ func refactorRewriteRemoveUnusedParam(ctx context.Context, req *codeActionsReque
 }
 
 func refactorRewriteMoveParamLeft(ctx context.Context, req *codeActionsRequest) error {
-	if info := findParam(req.pgf, req.loc.Range); info != nil && info.paramIndex > 0 {
+	if info := findParam(req.pgf, req.loc.Range); info != nil &&
+		info.paramIndex > 0 &&
+		!is[*ast.Ellipsis](info.field.Type) {
+
+		// ^^ we can't currently handle moving a variadic param.
+		// TODO(rfindley): implement.
 
 		transform := identityTransform(info.decl.Type.Params)
 		transform[info.paramIndex] = command.ChangeSignatureParam{OldIndex: info.paramIndex - 1}
@@ -566,19 +571,27 @@ func refactorRewriteMoveParamLeft(ctx context.Context, req *codeActionsRequest)
 }
 
 func refactorRewriteMoveParamRight(ctx context.Context, req *codeActionsRequest) error {
-	if info := findParam(req.pgf, req.loc.Range); info != nil && info.paramIndex >= 0 && // found a param
-		info.paramIndex < info.decl.Type.Params.NumFields()-1 { // not the last param
+	if info := findParam(req.pgf, req.loc.Range); info != nil && info.paramIndex >= 0 {
+		params := info.decl.Type.Params
+		nparams := params.NumFields()
+		if info.paramIndex < nparams-1 { // not the last param
+			if info.paramIndex == nparams-2 && is[*ast.Ellipsis](params.List[len(params.List)-1].Type) {
+				// We can't currently handle moving a variadic param.
+				// TODO(rfindley): implement.
+				return nil
+			}
 
-		transform := identityTransform(info.decl.Type.Params)
-		transform[info.paramIndex] = command.ChangeSignatureParam{OldIndex: info.paramIndex + 1}
-		transform[info.paramIndex+1] = command.ChangeSignatureParam{OldIndex: info.paramIndex}
-		cmd := command.NewChangeSignatureCommand("Move parameter right", command.ChangeSignatureArgs{
-			Location:     req.loc,
-			NewParams:    transform,
-			NewResults:   identityTransform(info.decl.Type.Results),
-			ResolveEdits: req.resolveEdits(),
-		})
-		req.addCommandAction(cmd, true)
+			transform := identityTransform(info.decl.Type.Params)
+			transform[info.paramIndex] = command.ChangeSignatureParam{OldIndex: info.paramIndex + 1}
+			transform[info.paramIndex+1] = command.ChangeSignatureParam{OldIndex: info.paramIndex}
+			cmd := command.NewChangeSignatureCommand("Move parameter right", command.ChangeSignatureArgs{
+				Location:     req.loc,
+				NewParams:    transform,
+				NewResults:   identityTransform(info.decl.Type.Results),
+				ResolveEdits: req.resolveEdits(),
+			})
+			req.addCommandAction(cmd, true)
+		}
 	}
 	return nil
 }

gopls/internal/test/marker/marker_test.go

@@ -11,6 +11,7 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"go/token"
@@ -2250,10 +2251,12 @@ func codeActionChanges(env *integration.Env, uri protocol.DocumentURI, rng proto
 		}
 	}
 	if len(candidates) != 1 {
+		var msg bytes.Buffer
+		fmt.Fprintf(&msg, "found %d CodeActions of kind %s for this diagnostic, want 1", len(candidates), kind)
 		for _, act := range actions {
-			env.T.Logf("found CodeAction Kind=%s Title=%q", act.Kind, act.Title)
+			fmt.Fprintf(&msg, "\n\tfound %q (%s)", act.Title, act.Kind)
 		}
-		return nil, fmt.Errorf("found %d CodeActions of kind %s for this diagnostic, want 1", len(candidates), kind)
+		return nil, errors.New(msg.String())
 	}
 	action := candidates[0]
 

gopls/internal/test/marker/testdata/codeaction/moveparam_issue70599.txt

@@ -94,7 +94,7 @@ package a
 // We should not offer movement involving variadic parameters if it is not well
 // supported.
 
-func Variadic(x int, y ...string) { //@codeaction("x", "refactor.rewrite.moveParamRight", err="type checking rewritten package")
+func Variadic(x int, y ...string) { //@codeaction("x", "refactor.rewrite.moveParamRight", err="0 CodeActions"), codeaction("y", "refactor.rewrite.moveParamLeft", err="0 CodeActions")
 }
 
 func _() {