Add support for external diff commands (e.g. difftastic)

docs/Custom_Pagers.md

@@ -62,3 +62,25 @@ git:
 ```
 
 If you set `useConfig: true`, lazygit will use whatever pager is specified in `$GIT_PAGER`, `$PAGER`, or your *git config*. If the pager ends with something like ` | less` we will strip that part out, because less doesn't play nice with our rendering approach. If the custom pager uses less under the hood, that will also break rendering (hence the `--paging=never` flag for the `delta` pager).
+
+## Using external diff commands
+
+Some diff tools can't work as a simple pager like the ones above do, because they need access to the entire diff, so just post-processing git's diff is not enough for them. The most notable example is probably [difftastic](https://difftastic.wilfred.me.uk).
+
+These can be used in lazygit by using the `externalDiffCommand` config; in the case of difftastic, that could be
+
+```yaml
+git:
+  paging:
+    externalDiffCommand: difft --color=always
+```
+
+The `colorArg`, `pager`, and `useConfig` options are not used in this case.
+
+You can add whatever extra arguments you prefer for your difftool; for instance
+
+```yaml
+git:
+  paging:
+    externalDiffCommand: difft --color=always --display=inline --syntax-highlight=off
+```

pkg/commands/git_commands/commit.go

@@ -199,9 +199,11 @@ func (self *CommitCommands) AmendHeadCmdObj() oscommands.ICmdObj {
 func (self *CommitCommands) ShowCmdObj(sha string, filterPath string, ignoreWhitespace bool) oscommands.ICmdObj {
 	contextSize := self.UserConfig.Git.DiffContextSize
 
+	extDiffCmd := self.UserConfig.Git.Paging.ExternalDiffCommand
 	cmdArgs := NewGitCmd("show").
+		ConfigIf(extDiffCmd != "", "diff.external="+extDiffCmd).
+		ArgIfElse(extDiffCmd != "", "--ext-diff", "--no-ext-diff").
 		Arg("--submodule").
-		Arg("--no-ext-diff").
 		Arg("--color="+self.UserConfig.Git.Paging.ColorArg).
 		Arg(fmt.Sprintf("--unified=%d", contextSize)).
 		Arg("--stat").

pkg/commands/git_commands/commit_test.go

@@ -186,6 +186,7 @@ func TestCommitShowCmdObj(t *testing.T) {
 		filterPath       string
 		contextSize      int
 		ignoreWhitespace bool
+		extDiffCmd       string
 		expected         []string
 	}
 
@@ -195,28 +196,40 @@ func TestCommitShowCmdObj(t *testing.T) {
 			filterPath:       "",
 			contextSize:      3,
 			ignoreWhitespace: false,
-			expected:         []string{"show", "--submodule", "--no-ext-diff", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890"},
+			extDiffCmd:       "",
+			expected:         []string{"show", "--no-ext-diff", "--submodule", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890"},
 		},
 		{
 			testName:         "Default case with filter path",
 			filterPath:       "file.txt",
 			contextSize:      3,
 			ignoreWhitespace: false,
-			expected:         []string{"show", "--submodule", "--no-ext-diff", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890", "--", "file.txt"},
+			extDiffCmd:       "",
+			expected:         []string{"show", "--no-ext-diff", "--submodule", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890", "--", "file.txt"},
 		},
 		{
 			testName:         "Show diff with custom context size",
 			filterPath:       "",
 			contextSize:      77,
 			ignoreWhitespace: false,
-			expected:         []string{"show", "--submodule", "--no-ext-diff", "--color=always", "--unified=77", "--stat", "--decorate", "-p", "1234567890"},
+			extDiffCmd:       "",
+			expected:         []string{"show", "--no-ext-diff", "--submodule", "--color=always", "--unified=77", "--stat", "--decorate", "-p", "1234567890"},
 		},
 		{
 			testName:         "Show diff, ignoring whitespace",
 			filterPath:       "",
 			contextSize:      77,
 			ignoreWhitespace: true,
-			expected:         []string{"show", "--submodule", "--no-ext-diff", "--color=always", "--unified=77", "--stat", "--decorate", "-p", "1234567890", "--ignore-all-space"},
+			extDiffCmd:       "",
+			expected:         []string{"show", "--no-ext-diff", "--submodule", "--color=always", "--unified=77", "--stat", "--decorate", "-p", "1234567890", "--ignore-all-space"},
+		},
+		{
+			testName:         "Show diff with external diff command",
+			filterPath:       "",
+			contextSize:      3,
+			ignoreWhitespace: false,
+			extDiffCmd:       "difft --color=always",
+			expected:         []string{"-c", "diff.external=difft --color=always", "show", "--ext-diff", "--submodule", "--color=always", "--unified=3", "--stat", "--decorate", "-p", "1234567890"},
 		},
 	}
 
@@ -225,6 +238,7 @@ func TestCommitShowCmdObj(t *testing.T) {
 		t.Run(s.testName, func(t *testing.T) {
 			userConfig := config.GetDefaultConfig()
 			userConfig.Git.DiffContextSize = s.contextSize
+			userConfig.Git.Paging.ExternalDiffCommand = s.extDiffCmd
 
 			runner := oscommands.NewFakeRunner(t).ExpectGitArgs(s.expected, "", nil)
 			instance := buildCommitCommands(commonDeps{userConfig: userConfig, runner: runner})

pkg/commands/git_commands/git_command_builder.go

@@ -44,6 +44,14 @@ func (self *GitCommandBuilder) Config(value string) *GitCommandBuilder {
 	return self
 }
 
+func (self *GitCommandBuilder) ConfigIf(condition bool, ifTrue string) *GitCommandBuilder {
+	if condition {
+		self.Config(ifTrue)
+	}
+
+	return self
+}
+
 // the -C arg will make git do a `cd` to the directory before doing anything else
 func (self *GitCommandBuilder) Dir(path string) *GitCommandBuilder {
 	// repo path comes before the command

pkg/commands/git_commands/working_tree.go

@@ -243,10 +243,13 @@ func (self *WorkingTreeCommands) WorktreeFileDiffCmdObj(node models.IFile, plain
 	contextSize := self.UserConfig.Git.DiffContextSize
 	prevPath := node.GetPreviousPath()
 	noIndex := !node.GetIsTracked() && !node.GetHasStagedChanges() && !cached && node.GetIsFile()
+	extDiffCmd := self.UserConfig.Git.Paging.ExternalDiffCommand
+	useExtDiff := extDiffCmd != "" && !plain
 
 	cmdArgs := NewGitCmd("diff").
+		ConfigIf(useExtDiff, "diff.external="+extDiffCmd).
+		ArgIfElse(useExtDiff, "--ext-diff", "--no-ext-diff").
 		Arg("--submodule").
-		Arg("--no-ext-diff").
 		Arg(fmt.Sprintf("--unified=%d", contextSize)).
 		Arg(fmt.Sprintf("--color=%s", colorArg)).
 		ArgIf(ignoreWhitespace, "--ignore-all-space").
@@ -279,9 +282,13 @@ func (self *WorkingTreeCommands) ShowFileDiffCmdObj(from string, to string, reve
 		colorArg = "never"
 	}
 
+	extDiffCmd := self.UserConfig.Git.Paging.ExternalDiffCommand
+	useExtDiff := extDiffCmd != "" && !plain
+
 	cmdArgs := NewGitCmd("diff").
+		ConfigIf(useExtDiff, "diff.external="+extDiffCmd).
+		ArgIfElse(useExtDiff, "--ext-diff", "--no-ext-diff").
 		Arg("--submodule").
-		Arg("--no-ext-diff").
 		Arg(fmt.Sprintf("--unified=%d", contextSize)).
 		Arg("--no-renames").
 		Arg(fmt.Sprintf("--color=%s", colorArg)).

pkg/commands/git_commands/working_tree_test.go

@@ -231,7 +231,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--color=always", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--color=always", "--", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName: "cached",
@@ -245,7 +245,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--color=always", "--cached", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--color=always", "--cached", "--", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName: "plain",
@@ -259,7 +259,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--color=never", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--color=never", "--", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName: "File not tracked and file has no staged changes",
@@ -273,7 +273,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--color=always", "--no-index", "--", "/dev/null", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--color=always", "--no-index", "--", "/dev/null", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName: "Default case (ignore whitespace)",
@@ -287,7 +287,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 			ignoreWhitespace: true,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--color=always", "--ignore-all-space", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--color=always", "--ignore-all-space", "--", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName: "Show diff with custom context size",
@@ -301,7 +301,7 @@ func TestWorkingTreeDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      17,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=17", "--color=always", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=17", "--color=always", "--", "test.txt"}, expectedResult, nil),
 		},
 	}
 
@@ -343,7 +343,7 @@ func TestWorkingTreeShowFileDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--no-renames", "--color=always", "1234567890", "0987654321", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--no-renames", "--color=always", "1234567890", "0987654321", "--", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName:         "Show diff with custom context size",
@@ -354,7 +354,7 @@ func TestWorkingTreeShowFileDiff(t *testing.T) {
 			ignoreWhitespace: false,
 			contextSize:      123,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=123", "--no-renames", "--color=always", "1234567890", "0987654321", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=123", "--no-renames", "--color=always", "1234567890", "0987654321", "--", "test.txt"}, expectedResult, nil),
 		},
 		{
 			testName:         "Default case (ignore whitespace)",
@@ -365,7 +365,7 @@ func TestWorkingTreeShowFileDiff(t *testing.T) {
 			ignoreWhitespace: true,
 			contextSize:      3,
 			runner: oscommands.NewFakeRunner(t).
-				ExpectGitArgs([]string{"diff", "--submodule", "--no-ext-diff", "--unified=3", "--no-renames", "--color=always", "1234567890", "0987654321", "--ignore-all-space", "--", "test.txt"}, expectedResult, nil),
+				ExpectGitArgs([]string{"diff", "--no-ext-diff", "--submodule", "--unified=3", "--no-renames", "--color=always", "1234567890", "0987654321", "--ignore-all-space", "--", "test.txt"}, expectedResult, nil),
 		},
 	}
 

pkg/config/user_config.go

@@ -104,6 +104,7 @@ type PagingConfig struct {
 	ColorArg            string `yaml:"colorArg"`
 	Pager               string `yaml:"pager"`
 	UseConfig           bool   `yaml:"useConfig"`
+	ExternalDiffCommand string `yaml:"externalDiffCommand"`
 }
 
 type CommitConfig struct {
@@ -472,6 +473,7 @@ func GetDefaultConfig() *UserConfig {
 				ColorArg:            "always",
 				Pager:               "",
 				UseConfig:           false,
+				ExternalDiffCommand: "",
 			},
 			Commit: CommitConfig{
 				SignOff: false,