[pull] trunk from cli:trunk

.github/CONTRIBUTING.md

@@ -2,19 +2,19 @@
 
 Hi! Thanks for your interest in contributing to the GitHub CLI!
 
-We accept pull requests for bug fixes and features where we've discussed the approach in an issue and given the go-ahead for a community member to work on it. We'd also love to hear about ideas for new features as issues.
+We accept pull requests for issues labelled `help wanted`. We encourage issues and discussion posts for all other contributions.
 
 ### Please do:
 
 * Check issues to verify that a [bug][bug issues] or [feature request][feature request issues] issue does not already exist for the same problem or feature
 * Open an issue if things aren't working as expected
-* Open an issue to propose a significant change
+* Open an issue to propose a change
 * Open an issue to propose a design for an issue labelled [`needs-design` and `help wanted`][needs design and help wanted], following the [proposing a design guidelines](#proposing-a-design) instructions below
 * Open an issue to propose a new community supported `gh` package with details about support and redistribution
 * Mention `@cli/code-reviewers` when an issue you want to work on does not have clear Acceptance Criteria
 * Open a pull request for any issue labelled [`help wanted`][hw] and [`good first issue`][gfi]
 
-### Please _do not_:
+### Please _do NOT_:
 
 * Open a pull request for issues without the `help wanted` label or explicit Acceptance Criteria
 * Expand pull request scope to include changes that are not described in the issue's Acceptance Criteria

pkg/cmd/pr/create/create.go

@@ -166,6 +166,16 @@ func (r forkableRefs) UnqualifiedHeadRef() string {
 	return r.qualifiedHeadRef.BranchName()
 }
 
+// isSameRef checks if the head and base refs point to the same ref in the same repository.
+// For cross-repository PRs (e.g., from a fork), the qualified head ref will contain
+// an owner prefix (owner:branch), so even if branch names match, they refer to different repos.
+func isSameRef(refs creationRefs) bool {
+	if strings.Contains(refs.QualifiedHeadRef(), ":") {
+		return false
+	}
+	return refs.UnqualifiedHeadRef() == refs.BaseRef()
+}
+
 // CreateContext stores contextual data about the creation process and is for building up enough
 // data to create a pull request.
 type CreateContext struct {
@@ -367,6 +377,10 @@ func createRun(opts *CreateOptions) error {
 		return err
 	}
 
+	if isSameRef(ctx.PRRefs) {
+		return fmt.Errorf("head branch %q is the same as base branch %q, cannot create a pull request", ctx.PRRefs.UnqualifiedHeadRef(), ctx.PRRefs.BaseRef())
+	}
+
 	httpClient, err := opts.HttpClient()
 	if err != nil {
 		return err

pkg/cmd/pr/create/create_test.go

@@ -384,6 +384,31 @@ func Test_createRun(t *testing.T) {
 			},
 			expectedOut: "https://github.com/OWNER/REPO/pull/12\n",
 		},
+		{
+			name: "same head and base branch should error",
+			setup: func(opts *CreateOptions, t *testing.T) func() {
+				opts.TitleProvided = true
+				opts.BodyProvided = true
+				opts.Title = "my title"
+				opts.Body = "my body"
+				opts.HeadBranch = "master"
+				return func() {}
+			},
+			wantErr: `head branch "master" is the same as base branch "master", cannot create a pull request`,
+		},
+		{
+			name: "same head and base branch with explicit base should error",
+			setup: func(opts *CreateOptions, t *testing.T) func() {
+				opts.TitleProvided = true
+				opts.BodyProvided = true
+				opts.Title = "my title"
+				opts.Body = "my body"
+				opts.HeadBranch = "feature"
+				opts.BaseBranch = "feature"
+				return func() {}
+			},
+			wantErr: `head branch "feature" is the same as base branch "feature", cannot create a pull request`,
+		},
 		{
 			name: "dry-run-nontty-with-default-base",
 			tty:  false,
@@ -2879,3 +2904,73 @@ func TestProjectsV1Deprecation(t *testing.T) {
 		})
 	})
 }
+
+func Test_isSameRef(t *testing.T) {
+	tests := []struct {
+		name     string
+		refs     creationRefs
+		expected bool
+	}{
+		{
+			name: "same branch in same repo",
+			refs: skipPushRefs{
+				qualifiedHeadRef: shared.NewQualifiedHeadRefWithoutOwner("main"),
+				baseRefs: baseRefs{
+					baseBranchName: "main",
+				},
+			},
+			expected: true,
+		},
+		{
+			name: "different branches in same repo",
+			refs: skipPushRefs{
+				qualifiedHeadRef: shared.NewQualifiedHeadRefWithoutOwner("feature"),
+				baseRefs: baseRefs{
+					baseBranchName: "main",
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "same branch name in different repos (cross-repo PR)",
+			refs: skipPushRefs{
+				qualifiedHeadRef: shared.NewQualifiedHeadRef("other-owner", "main"),
+				baseRefs: baseRefs{
+					baseBranchName: "main",
+				},
+			},
+			expected: false,
+		},
+		{
+			name: "pushableRefs same branch same repo",
+			refs: pushableRefs{
+				headRepo:       ghrepo.New("OWNER", "REPO"),
+				headBranchName: "main",
+				baseRefs: baseRefs{
+					baseRepo:       api.InitRepoHostname(&api.Repository{Name: "REPO", Owner: api.RepositoryOwner{Login: "OWNER"}}, "github.com"),
+					baseBranchName: "main",
+				},
+			},
+			expected: true,
+		},
+		{
+			name: "pushableRefs same branch different repos (fork)",
+			refs: pushableRefs{
+				headRepo:       ghrepo.New("FORK-OWNER", "REPO"),
+				headBranchName: "main",
+				baseRefs: baseRefs{
+					baseRepo:       api.InitRepoHostname(&api.Repository{Name: "REPO", Owner: api.RepositoryOwner{Login: "OWNER"}}, "github.com"),
+					baseBranchName: "main",
+				},
+			},
+			expected: false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			result := isSameRef(tt.refs)
+			assert.Equal(t, tt.expected, result)
+		})
+	}
+}