Add diff parent command (git-town#1385)

features/git-town-diff-parent/current_branch/on_feature_branch/no_parent_branch.feature

@@ -0,0 +1,22 @@
+Feature: git town-parent-diff: diffing the current feature branch
+
+    As a user running parent-diff
+    With no arguments
+    On a feature branch that has no parent branch defined
+    I should see a prompt to supply a parent branch
+    So that the command can work as I expect
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature" with no parent
+    And I am on the "feature" branch
+    When I run "git-town diff-parent" and answer the prompts:
+      | PROMPT                                        | ANSWER  |
+      | Please specify the parent branch of 'feature' | [ENTER] |
+    Then it runs the commands
+      | BRANCH  | COMMAND                |
+      | feature | git diff main..feature |
+    And I am still on the "feature" branch
+    And Git Town is now aware of this branch hierarchy
+      | BRANCH  | PARENT |
+      | feature | main   |

features/git-town-diff-parent/current_branch/on_feature_branch/with_parent_branch.feature

@@ -0,0 +1,17 @@
+Feature: git town-parent-diff: diffing the current feature branch
+
+    As a developer makeing changes to a feature branched created with Git Town
+    I want that Git Town tells me which changes this feature branch contains
+    So that I know what work is left to do
+    And which work will be merged into the parent branch
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature-1"
+    And my repository has a feature branch named "feature-2" as a child of "feature-1"
+    And I am on the "feature-2" branch
+    When I run "git-town diff-parent"
+    Then it runs the commands
+      | BRANCH    | COMMAND                       |
+      | feature-2 | git diff feature-1..feature-2 |
+    And I am still on the "feature-2" branch

features/git-town-diff-parent/current_branch/on_main_branch.feature

@@ -0,0 +1,17 @@
+Feature: git town-diff-parent: errors when trying to diff the main branch
+
+  As a developer accidentally trying to diff the main branch
+  I should see an error that I cannot diff the main branch
+  Because the master branch cannot have a parent branch
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature"
+    And I am on the "main" branch
+    When I run "git-town diff-parent"
+    Then it runs no commands
+    And it prints the error:
+      """
+      You can only diff-parent feature branches
+      """
+    And I am still on the "main" branch

features/git-town-diff-parent/current_branch/on_non_feature_branch.feature

@@ -0,0 +1,17 @@
+Feature: git town-diff-parent: errors when trying to diff a perennial branch
+
+  As a developer accidentally trying to diff a perennial branch
+  I should see an error that I cannot diff perennial branches
+  Because perennial branches cannot have parent branches
+
+
+  Scenario: result
+    Given my repository has the perennial branch "qa"
+    And I am on the "qa" branch
+    When I run "git-town diff-parent"
+    Then it runs no commands
+    And it prints the error:
+      """
+      You can only diff-parent feature branches
+      """
+    And I am still on the "qa" branch

features/git-town-diff-parent/supplied_branch/branch_does_not_exist.feature

@@ -0,0 +1,15 @@
+Feature: git town-diff-parent: errors if supplied branch does not exist
+
+  As a developer mistyping the branch name to diff against its parent
+  I should get an error that the given branch does not exist
+  So that I can diff the correct branch
+
+  Scenario: result
+    Given I am on the "main" branch
+    When I run "git-town diff-parent non-existing-feature"
+    Then it runs no commands
+    And it prints the error:
+      """
+      There is no local branch named 'non-existing-feature'
+      """
+    And I end up on the "main" branch

features/git-town-diff-parent/supplied_branch/feature_branch/on_main_branch.feature

@@ -0,0 +1,14 @@
+Feature: git town-diff-parent: diffing a given feature branch
+
+  (see ../../current_branch/on_feature_branch/with_parent_branches.feature)
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature-1"
+    And my repository has a feature branch named "feature-2" as a child of "feature-1"
+    And I am on the "main" branch
+    When I run "git-town diff-parent feature-2"
+    Then it runs the commands
+      | BRANCH | COMMAND                       |
+      | main   | git diff feature-1..feature-2 |
+    And I am still on the "main" branch

features/git-town-diff-parent/supplied_branch/feature_branch/on_main_branch_no_parent.feature

@@ -0,0 +1,22 @@
+Feature: git town-parent-diff: diffing the current feature branch
+
+    As a user running parent-diff
+    With a supplied branch
+    On the main branch
+    I should see a prompt to identify a parent branch
+    So that the command can work as I expect
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature" with no parent
+    And I am on the "main" branch
+    When I run "git-town diff-parent feature" and answer the prompts:
+      | PROMPT                                        | ANSWER  |
+      | Please specify the parent branch of 'feature' | [ENTER] |
+    Then it runs the commands
+      | BRANCH | COMMAND                |
+      | main   | git diff main..feature |
+    And I am still on the "main" branch
+    And Git Town is now aware of this branch hierarchy
+      | BRANCH  | PARENT |
+      | feature | main   |

features/git-town-diff-parent/supplied_branch/feature_branch/on_parent_branch.feature

@@ -0,0 +1,14 @@
+Feature: git town-diff-parent: diffing a given feature branch
+
+  (see ../../current_branch/on_feature_branch/with_parent_branches.feature)
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature-1"
+    And my repository has a feature branch named "feature-2" as a child of "feature-1"
+    And I am on the "feature-1" branch
+    When I run "git-town diff-parent feature-2"
+    Then it runs the commands
+      | BRANCH    | COMMAND                       |
+      | feature-1 | git diff feature-1..feature-2 |
+    And I am still on the "feature-1" branch

features/git-town-diff-parent/supplied_branch/main_branch.feature

@@ -0,0 +1,15 @@
+Feature: git town-diff-parent: errors when trying to diff the main branch
+
+  (see ../current_branch/on_main_branch.feature)
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature"
+    And I am on the "feature" branch
+    When I run "git-town diff-parent main"
+    Then it runs no commands
+    And it prints the error:
+      """
+      You can only diff-parent feature branches
+      """
+    And I am still on the "feature" branch

features/git-town-diff-parent/supplied_branch/on_supplied_feature_branch/has_parent.feature

@@ -0,0 +1,14 @@
+Feature: git town-diff-parent: diffing a given feature branch
+
+  (see ../../current_branch/on_feature_branch/with_parent_branch.feature)
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature-1"
+    And my repository has a feature branch named "feature-2" as a child of "feature-1"
+    And I am on the "feature-2" branch
+    When I run "git-town diff-parent feature-2"
+    Then it runs the commands
+      | BRANCH    | COMMAND                       |
+      | feature-2 | git diff feature-1..feature-2 |
+    And I am still on the "feature-2" branch

features/git-town-diff-parent/supplied_branch/on_supplied_feature_branch/no_parent_branch.feature

@@ -0,0 +1,22 @@
+Feature: git town-parent-diff: diffing the current feature branch
+
+    As a user running parent-diff
+    With a supplied branch that matches my current branch
+    On a branch that has no parent branch defined
+    I should see a prompt to supply a parent branch
+    So that the command can work as I expect
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature" with no parent
+    And I am on the "feature" branch
+    When I run "git-town diff-parent feature" and answer the prompts:
+      | PROMPT                                        | ANSWER  |
+      | Please specify the parent branch of 'feature' | [ENTER] |
+    Then it runs the commands
+      | BRANCH  | COMMAND                |
+      | feature | git diff main..feature |
+    And I am still on the "feature" branch
+    And Git Town is now aware of this branch hierarchy
+      | BRANCH  | PARENT |
+      | feature | main   |

features/git-town-diff-parent/supplied_branch/perennial_branch.feature

@@ -0,0 +1,16 @@
+Feature: git town-diff-parent: errors when trying to diff a perennial branch
+
+  (see ../current_branch/on_perennial_branch.feature)
+
+
+  Scenario: result
+    Given my repository has a feature branch named "feature"
+    And my repository has the perennial branch "qa"
+    And I am on the "feature" branch
+    When I run "git-town diff-parent qa"
+    Then it runs no commands
+    And it prints the error:
+      """
+      You can only diff-parent feature branches
+      """
+    And I am still on the "feature" branch

src/cmd/diff_parent.go

@@ -0,0 +1,60 @@
+package cmd
+
+import (
+	"github.com/git-town/git-town/src/git"
+	"github.com/git-town/git-town/src/prompt"
+	"github.com/git-town/git-town/src/script"
+	"github.com/git-town/git-town/src/util"
+	"github.com/spf13/cobra"
+)
+
+type diffParentConfig struct {
+	branch       string
+	parentBranch string
+}
+
+var diffParentCommand = &cobra.Command{
+	Use:   "diff-parent [<branch>]",
+	Short: "Shows the changes committed to a feature branch",
+	Long: `Shows the changes committed to a feature branch
+
+Works on either the current branch or the branch name provided.
+
+Exits with error code 1 if the given branch is a perennial branch or the main branch.`,
+	Run: func(cmd *cobra.Command, args []string) {
+		config := getDiffParentConfig(args)
+		script.RunCommandSafe("git", "diff", config.parentBranch+".."+config.branch)
+	},
+	Args: cobra.MaximumNArgs(1),
+	PreRunE: func(cmd *cobra.Command, args []string) error {
+		return util.FirstError(
+			git.ValidateIsRepository,
+			validateIsConfigured,
+		)
+	},
+}
+
+// Does not return error because "Ensure" functions will call exit directly
+func getDiffParentConfig(args []string) (config diffParentConfig) {
+	initialBranch := git.GetCurrentBranchName()
+
+	if len(args) == 0 {
+		config.branch = initialBranch
+	} else {
+		config.branch = args[0]
+	}
+
+	if initialBranch != config.branch {
+		git.EnsureHasLocalBranch(config.branch)
+	}
+
+	git.Config().EnsureIsFeatureBranch(config.branch, "You can only diff-parent feature branches.")
+
+	prompt.EnsureKnowsParentBranches([]string{config.branch})
+	config.parentBranch = git.Config().GetParentBranch(config.branch)
+	return
+}
+
+func init() {
+	RootCmd.AddCommand(diffParentCommand)
+}

src/git/branch.go

@@ -29,6 +29,11 @@ func EnsureHasBranch(branchName string) {
 	util.Ensure(HasBranch(branchName), fmt.Sprintf("There is no branch named '%s'", branchName))
 }
 
+// EnsureHasLocalBranch enforces that a local branch with the given name exists
+func EnsureHasLocalBranch(branchName string) {
+	util.Ensure(HasLocalBranch(branchName), fmt.Sprintf("There is no local branch named '%s'", branchName))
+}
+
 // EnsureIsNotMainBranch enforces that a branch with the given name is not the main branch
 func EnsureIsNotMainBranch(branchName, errorMessage string) {
 	util.Ensure(!Config().IsMainBranch(branchName), errorMessage)

test/git_repository.go

@@ -260,6 +260,17 @@ func (repo *GitRepository) CreateFeatureBranch(name string) error {
 	return nil
 }
 
+// CreateFeatureBranch creates a feature branch with no defined parent in this repository.
+func (repo *GitRepository) CreateFeatureBranchNoParent(name string) error {
+	err := repo.Shell.RunMany([][]string{
+		{"git", "checkout", "-b", name},
+	})
+	if err != nil {
+		return fmt.Errorf("cannot create feature branch %q: %w", name, err)
+	}
+	return nil
+}
+
 // CreateFile creates a file with the given name and content in this repository.
 func (repo *GitRepository) CreateFile(name, content string) error {
 	filePath := filepath.Join(repo.Dir, name)

test/git_repository_test.go

@@ -196,6 +196,15 @@ func TestGitRepository_CreateFeatureBranch(t *testing.T) {
 	err := repo.CreateFeatureBranch("f1")
 	assert.Nil(t, err)
 	assert.True(t, repo.Configuration(true).IsFeatureBranch("f1"))
+	assert.Equal(t, []string{"main"}, repo.Configuration(true).GetAncestorBranches("f1"))
+}
+
+func TestGitRepository_CreateFeatureBranchNoParent(t *testing.T) {
+	repo := createTestGitTownRepo(t)
+	err := repo.CreateFeatureBranchNoParent("f1")
+	assert.Nil(t, err)
+	assert.True(t, repo.Configuration(true).IsFeatureBranch("f1"))
+	assert.Equal(t, []string(nil), repo.Configuration(true).GetAncestorBranches("f1"))
 }
 
 func TestGitRepository_CreateFile(t *testing.T) {

test/steps/branch_steps.go

@@ -116,6 +116,10 @@ func BranchSteps(suite *godog.Suite, fs *FeatureState) {
 		return nil
 	})
 
+	suite.Step(`^my repository has a feature branch named "([^"]*)" with no parent$`, func(branch string) error {
+		return fs.activeScenarioState.gitEnvironment.DeveloperRepo.CreateFeatureBranchNoParent(branch)
+	})
+
 	suite.Step(`^my repository has a feature branch named "([^"]+)" as a child of "([^"]+)"$`, func(childBranch, parentBranch string) error {
 		err := fs.activeScenarioState.gitEnvironment.DeveloperRepo.CreateChildFeatureBranch(childBranch, parentBranch)
 		if err != nil {