cmd/gg: verify -dst argument in rebase

Fixes #127

Author: zombiezen

CHANGELOG.md

@@ -34,6 +34,8 @@ The format is based on [Keep a Changelog][], and this project adheres to
    ([#121](https://github.com/gg-scm/gg/issues/121))
 -  `commit --amend` no longer exits with an error if the commit contains a
    rename. ([#129](https://github.com/gg-scm/gg/issues/129))
+-  `rebase` displays a simpler error message if the `-dst` argument doesn't
+   exist. ([#127](https://github.com/gg-scm/gg/issues/127))
 
 ## [1.0.3][] - 2020-09-07
 

cmd/gg/rebase.go

@@ -28,15 +28,16 @@ import (
 const rebaseSynopsis = "move revision (and descendants) to a different branch"
 
 func rebase(ctx context.Context, cc *cmdContext, args []string) error {
+	const upstreamRev = "@{upstream}"
 	f := flag.NewFlagSet(true, "gg rebase [--src REV | --base REV] [--dst REV] [options]", rebaseSynopsis+`
 
 	Rebasing will replay a set of changes on top of the destination
 	revision and set the current branch to the final revision.
 
 	If neither `+"`--src`"+` or `+"`--base`"+` is specified, it acts as if
-	`+"`--base=@{upstream}`"+` was specified.`)
+	`+"`--base="+upstreamRev+"`"+` was specified.`)
 	base := f.String("base", "", "rebase everything from branching point of specified `rev`ision")
-	dst := f.String("dst", "@{upstream}", "rebase onto the specified `rev`ision")
+	dst := f.String("dst", upstreamRev, "rebase onto the specified `rev`ision")
 	src := f.String("src", "", "rebase the specified `rev`ision and descendants")
 	abort := f.Bool("abort", false, "abort an interrupted rebase")
 	continue_ := f.Bool("continue", false, "continue an interrupted rebase")
@@ -52,7 +53,7 @@ func rebase(ctx context.Context, cc *cmdContext, args []string) error {
 	if *abort && *continue_ {
 		return usagef("can't specify both --abort and --continue")
 	}
-	if (*abort || *continue_) && (*base != "" || *dst != "@{upstream}" || *src != "") {
+	if (*abort || *continue_) && (*base != "" || *dst != upstreamRev || *src != "") {
 		return usagef("can't specify other options with --abort or --continue")
 	}
 	if *abort {
@@ -61,6 +62,11 @@ func rebase(ctx context.Context, cc *cmdContext, args []string) error {
 	if *continue_ {
 		return continueRebase(ctx, cc)
 	}
+	// Verify that -dst exists to give the user a better error message.
+	// See https://github.com/gg-scm/gg/issues/127
+	if _, err := cc.git.ParseRev(ctx, *dst); err != nil {
+		return fmt.Errorf("destination: %w", err)
+	}
 	switch {
 	case *base != "" && *src != "":
 		return usagef("can't specify both -s and -b")

cmd/gg/rebase_test.go

@@ -569,6 +569,30 @@ func TestRebase_ResetUpstream(t *testing.T) {
 	})
 }
 
+func TestRebase_NoUpstream(t *testing.T) {
+	// Regression test for https://github.com/gg-scm/gg/issues/127
+
+	t.Parallel()
+	ctx := context.Background()
+	env, err := newTestEnv(ctx, t)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := env.initRepoWithHistory(ctx, "."); err != nil {
+		t.Fatal(err)
+	}
+
+	// Call gg rebase.
+	stdout, err := env.gg(ctx, env.root.String(), "rebase")
+	if err == nil {
+		t.Error("gg succeeded even though it should have returned an error")
+	} else {
+		t.Log(err)
+		t.Logf("%s", stdout)
+	}
+}
+
 func TestHistedit(t *testing.T) {
 	t.Parallel()
 	runRebaseArgVariants(t, func(t *testing.T, argFunc rebaseArgFunc) {
@@ -1001,6 +1025,30 @@ func TestHistedit_ContinueNoModifications(t *testing.T) {
 	})
 }
 
+func TestHistedit_NoUpstream(t *testing.T) {
+	// Regression test for https://github.com/gg-scm/gg/issues/127
+
+	t.Parallel()
+	ctx := context.Background()
+	env, err := newTestEnv(ctx, t)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if err := env.initRepoWithHistory(ctx, "."); err != nil {
+		t.Fatal(err)
+	}
+
+	// Call gg histedit.
+	stdout, err := env.gg(ctx, env.root.String(), "histedit")
+	if err == nil {
+		t.Error("gg succeeded even though it should have returned an error")
+	} else {
+		t.Log(err)
+		t.Logf("%s", stdout)
+	}
+}
+
 type rebaseArgFunc = func(mainCommit git.Hash) string
 
 func runRebaseArgVariants(t *testing.T, f func(*testing.T, rebaseArgFunc)) {