Non-sticky range selection diff (#3869)

- **PR Description**

When selecting a range of commits, show the combined diff for them.

Along the way, fix a few minor issues with the current implementation of
diffing mode; see the individual commit messages for details.

Fixes #3862.

- **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))
* [x] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [x] 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

Author: stefanhaller

pkg/commands/models/branch.go

@@ -53,6 +53,10 @@ func (b *Branch) RefName() string {
 	return b.Name
 }
 
+func (b *Branch) ShortRefName() string {
+	return b.RefName()
+}
+
 func (b *Branch) ParentRefName() string {
 	return b.RefName() + "^"
 }

pkg/commands/models/commit.go

@@ -70,6 +70,10 @@ func (c *Commit) RefName() string {
 	return c.Hash
 }
 
+func (c *Commit) ShortRefName() string {
+	return c.Hash[:7]
+}
+
 func (c *Commit) ParentRefName() string {
 	if c.IsFirstCommit() {
 		return EmptyTreeCommitHash

pkg/commands/models/remote_branch.go

@@ -18,6 +18,10 @@ func (r *RemoteBranch) RefName() string {
 	return r.FullName()
 }
 
+func (r *RemoteBranch) ShortRefName() string {
+	return r.RefName()
+}
+
 func (r *RemoteBranch) ParentRefName() string {
 	return r.RefName() + "^"
 }

pkg/commands/models/stash_entry.go

@@ -17,6 +17,10 @@ func (s *StashEntry) RefName() string {
 	return fmt.Sprintf("stash@{%d}", s.Index)
 }
 
+func (s *StashEntry) ShortRefName() string {
+	return s.RefName()
+}
+
 func (s *StashEntry) ParentRefName() string {
 	return s.RefName() + "^"
 }

pkg/commands/models/tag.go

@@ -16,6 +16,10 @@ func (t *Tag) RefName() string {
 	return t.Name
 }
 
+func (t *Tag) ShortRefName() string {
+	return t.RefName()
+}
+
 func (t *Tag) ParentRefName() string {
 	return t.RefName() + "^"
 }

pkg/gui/context/commit_files_context.go

@@ -1,6 +1,8 @@
 package context
 
 import (
+	"fmt"
+
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands/models"
 	"github.com/jesseduffield/lazygit/pkg/gui/filetree"
@@ -75,6 +77,25 @@ func (self *CommitFilesContext) GetDiffTerminals() []string {
 	return []string{self.GetRef().RefName()}
 }
 
+func (self *CommitFilesContext) GetFromAndToForDiff() (string, string) {
+	if refs := self.GetRefRange(); refs != nil {
+		return refs.From.ParentRefName(), refs.To.RefName()
+	}
+	ref := self.GetRef()
+	return ref.ParentRefName(), ref.RefName()
+}
+
 func (self *CommitFilesContext) ModelSearchResults(searchStr string, caseSensitive bool) []gocui.SearchPosition {
 	return nil
 }
+
+func (self *CommitFilesContext) ReInit(ref types.Ref, refRange *types.RefRange) {
+	self.SetRef(ref)
+	self.SetRefRange(refRange)
+	if refRange != nil {
+		self.SetTitleRef(fmt.Sprintf("%s-%s", refRange.From.ShortRefName(), refRange.To.ShortRefName()))
+	} else {
+		self.SetTitleRef(ref.Description())
+	}
+	self.GetView().Title = self.Title()
+}

pkg/gui/context/local_commits_context.go

@@ -128,6 +128,19 @@ func (self *LocalCommitsContext) GetSelectedRef() types.Ref {
 	return commit
 }
 
+func (self *LocalCommitsContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	commits, startIdx, endIdx := self.GetSelectedItems()
+	if commits == nil || startIdx == endIdx {
+		return nil
+	}
+	from := commits[len(commits)-1]
+	to := commits[0]
+	if from.IsTODO() || to.IsTODO() {
+		return nil
+	}
+	return &types.RefRange{From: from, To: to}
+}
+
 // Returns the commit hash of the selected commit, or an empty string if no
 // commit is selected
 func (self *LocalCommitsContext) GetSelectedCommitHash() string {

pkg/gui/context/reflog_commits_context.go

@@ -71,6 +71,11 @@ func (self *ReflogCommitsContext) GetSelectedRef() types.Ref {
 	return commit
 }
 
+func (self *ReflogCommitsContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	// It doesn't make much sense to show a range diff between two reflog entries.
+	return nil
+}
+
 func (self *ReflogCommitsContext) GetCommits() []*models.Commit {
 	return self.getModel()
 }

pkg/gui/context/stash_context.go

@@ -61,6 +61,11 @@ func (self *StashContext) GetSelectedRef() types.Ref {
 	return stash
 }
 
+func (self *StashContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	// It doesn't make much sense to show a range diff between two stash entries.
+	return nil
+}
+
 func (self *StashContext) GetDiffTerminals() []string {
 	itemId := self.GetSelectedItemId()
 

pkg/gui/context/sub_commits_context.go

@@ -186,6 +186,19 @@ func (self *SubCommitsContext) GetSelectedRef() types.Ref {
 	return commit
 }
 
+func (self *SubCommitsContext) GetSelectedRefRangeForDiffFiles() *types.RefRange {
+	commits, startIdx, endIdx := self.GetSelectedItems()
+	if commits == nil || startIdx == endIdx {
+		return nil
+	}
+	from := commits[len(commits)-1]
+	to := commits[0]
+	if from.Divergence != to.Divergence {
+		return nil
+	}
+	return &types.RefRange{From: from, To: to}
+}
+
 func (self *SubCommitsContext) GetCommits() []*models.Commit {
 	return self.getModel()
 }