Use custom context size in range diff (#4082)

- **PR Description**

I just noticed that we don't respect the diff context size when showing
a range diff (both the "sticky" range diff when diffing mode is on, and
the more temporary one when selecting a range of commits). Here's a
quick fix for that.

I was too lazy to add tests for this, let me know if you would find this
important. Right now, it seems we only have tests for the context size
in the staging view, not in any of the other places where diffs can be
shown.

- **Please check if the PR fulfills these requirements**

* [x] Cheatsheets are up-to-date (run `go generate ./...`)
* [x] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [ ] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [ ] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [ ] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [ ] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

pkg/commands/git_commands/diff.go

@@ -19,6 +19,7 @@ func NewDiffCommands(gitCommon *GitCommon) *DiffCommands {
 func (self *DiffCommands) DiffCmdObj(diffArgs []string) oscommands.ICmdObj {
 	extDiffCmd := self.UserConfig().Git.Paging.ExternalDiffCommand
 	useExtDiff := extDiffCmd != ""
+	ignoreWhitespace := self.AppState.IgnoreWhitespaceInDiffView
 
 	return self.cmd.New(
 		NewGitCmd("diff").
@@ -27,6 +28,8 @@ func (self *DiffCommands) DiffCmdObj(diffArgs []string) oscommands.ICmdObj {
 			ArgIfElse(useExtDiff, "--ext-diff", "--no-ext-diff").
 			Arg("--submodule").
 			Arg(fmt.Sprintf("--color=%s", self.UserConfig().Git.Paging.ColorArg)).
+			ArgIf(ignoreWhitespace, "--ignore-all-space").
+			Arg(fmt.Sprintf("--unified=%d", self.AppState.DiffContextSize)).
 			Arg(diffArgs...).
 			Dir(self.repoPaths.worktreePath).
 			ToArgv(),

pkg/gui/controllers/helpers/diff_helper.go

@@ -34,10 +34,6 @@ func (self *DiffHelper) DiffArgs() []string {
 		output = append(output, "-R")
 	}
 
-	if self.c.GetAppState().IgnoreWhitespaceInDiffView {
-		output = append(output, "--ignore-all-space")
-	}
-
 	output = append(output, "--")
 
 	file := self.currentlySelectedFilename()
@@ -59,9 +55,6 @@ func (self *DiffHelper) GetUpdateTaskForRenderingCommitsDiff(commit *models.Comm
 	if refRange != nil {
 		from, to := refRange.From, refRange.To
 		args := []string{from.ParentRefName(), to.RefName(), "--stat", "-p"}
-		if self.c.GetAppState().IgnoreWhitespaceInDiffView {
-			args = append(args, "--ignore-all-space")
-		}
 		args = append(args, "--")
 		if path := self.c.Modes().Filtering.GetPath(); path != "" {
 			args = append(args, path)