Add go wrapper around git diff-tree --raw -r -M

[McRaeAlex]

• Implemented calling git diff-tree
• Ensures wrapper function is called with valid arguments
• Parses output into go struct, using strong typing when possible

[McRaeAlex]

Context for this PR: This was split out of a larger PR I hope to upstream to gitea for showing all files in a file tree at once rather than having a show more button at the bottom.

Note that this wouldn't change the behaviour of the files list to the right of the file tree. (Lets have that discussion in the PR which modifies the frontend)

[lunny]

And if it's for the left tree of git comparing, I don't think the structure is enough. Maybe it should like

type TreeViewNode struct {
	Name         string          `json:"name"`
	Type         string          `json:"type"`
	Path         string          `json:"path"`
	SubModuleURL string          `json:"sub_module_url,omitempty"`
	Children     []*TreeViewNode `json:"children,omitempty"`
}

This will be introduced in https://github.com/go-gitea/gitea/pull/32721/files#diff-ab9647487f3912999527f743b0fcada9b0bf1858b95e0bb7a684cc9fa383b157

[McRaeAlex]

And if it's for the left tree of git comparing, I don't think the structure is enough. Maybe it should like

type TreeViewNode struct {
	Name         string          `json:"name"`
	Type         string          `json:"type"`
	Path         string          `json:"path"`
	SubModuleURL string          `json:"sub_module_url,omitempty"`
	Children     []*TreeViewNode `json:"children,omitempty"`
}

This will be introduced in https://github.com/go-gitea/gitea/pull/32721/files#diff-ab9647487f3912999527f743b0fcada9b0bf1858b95e0bb7a684cc9fa383b157

The way I did this for allspice was the same structure as this with a function for transforming from output of git diff-tree to something more consumable by the UI.

Heres the function we are using in allspice.

type FileDiffFile struct {
	Name        string
	NameHash    string
	IsSubmodule bool
	IsBinary    bool
	IsViewed    bool
	Status      string
}

// transformDiffTreeForUI transforms a DiffTree into a slice of FileDiffFile for UI rendering
// it also takes a map of file names to their viewed state, which is used to mark files as viewed
func transformDiffTreeForUI(diffTree *gitdiff.DiffTree, filesViewedState map[string]pull_model.ViewedState) []FileDiffFile {
	files := make([]FileDiffFile, 0, len(diffTree.Files))

	for _, file := range diffTree.Files {
		nameHash := git.HashFilePathForWebUI(file.HeadPath)
		isSubmodule := file.HeadMode == git.EntryModeCommit
		isBinary := file.HeadMode == git.EntryModeExec

		isViewed := false
		if fileViewedState, ok := filesViewedState[file.Path()]; ok {
			isViewed = (fileViewedState == pull_model.Viewed)
		}

		files = append(files, FileDiffFile{
			Name:        file.HeadPath,
			NameHash:    nameHash,
			IsSubmodule: isSubmodule,
			IsBinary:    isBinary,
			IsViewed:    isViewed,
			Status:      file.Status,
		})
	}

	return files
}

This allows it to be used in box.tmpl

gitea/templates/repo/diff/box.tmpl

Line 61 in f88dbf8

const diffDataFiles = [{{range $i, $file := .Diff.Files}}{Name:"{{$file.Name}}",NameHash:"{{$file.NameHash}}",Type:{{$file.Type}},IsBin:{{$file.IsBin}},IsSubmodule:{{$file.IsSubmodule}},Addition:{{$file.Addition}},Deletion:{{$file.Deletion}},IsViewed:{{$file.IsViewed}}},{{end}}];

with some other minor modifications (like removing the code which relies on Added and Deleted).

[delvh]

Inherently, this method belongs into modules/git.
However, I'm also fine with declaring it here as it is directly below its usage.
Moving it would be important if we wanted the same information elsewhere.

[McRaeAlex]

I am somewhat unfamiliar with what goes where in gitea. I put it here because the wrapper around git diff used by pull requests go here.

[delvh]

Generally:

• routers: routing logic
• services: logic
• models: database access
• modules: low-level stuff that doesn't depend on anything else, i.e. calling git.

But as I said, it's fine as it is for now.

[lunny]

And if it's for the left tree of git comparing, I don't think the structure is enough. Maybe it should like

type TreeViewNode struct {
	Name         string          `json:"name"`
	Type         string          `json:"type"`
	Path         string          `json:"path"`
	SubModuleURL string          `json:"sub_module_url,omitempty"`
	Children     []*TreeViewNode `json:"children,omitempty"`
}

This will be introduced in #32721 (files)

The way I did this for allspice was the same structure as this with a function for transforming from output of git diff-tree to something more consumable by the UI.

Heres the function we are using in allspice.

type FileDiffFile struct {
	Name        string
	NameHash    string
	IsSubmodule bool
	IsBinary    bool
	IsViewed    bool
	Status      string
}

// transformDiffTreeForUI transforms a DiffTree into a slice of FileDiffFile for UI rendering
// it also takes a map of file names to their viewed state, which is used to mark files as viewed
func transformDiffTreeForUI(diffTree *gitdiff.DiffTree, filesViewedState map[string]pull_model.ViewedState) []FileDiffFile {
	files := make([]FileDiffFile, 0, len(diffTree.Files))

	for _, file := range diffTree.Files {
		nameHash := git.HashFilePathForWebUI(file.HeadPath)
		isSubmodule := file.HeadMode == git.EntryModeCommit
		isBinary := file.HeadMode == git.EntryModeExec

		isViewed := false
		if fileViewedState, ok := filesViewedState[file.Path()]; ok {
			isViewed = (fileViewedState == pull_model.Viewed)
		}

		files = append(files, FileDiffFile{
			Name:        file.HeadPath,
			NameHash:    nameHash,
			IsSubmodule: isSubmodule,
			IsBinary:    isBinary,
			IsViewed:    isViewed,
			Status:      file.Status,
		})
	}

	return files
}

This allows it to be used in box.tmpl

gitea/templates/repo/diff/box.tmpl

Line 61 in f88dbf8

const diffDataFiles = [{{range $i, $file := .Diff.Files}}{Name:"{{$file.Name}}",NameHash:"{{$file.NameHash}}",Type:{{$file.Type}},IsBin:{{$file.IsBin}},IsSubmodule:{{$file.IsSubmodule}},Addition:{{$file.Addition}},Deletion:{{$file.Deletion}},IsViewed:{{$file.IsViewed}}},{{end}}];

with some other minor modifications (like removing the code which relies on Added and Deleted).

Since we are rewriting the logic, maybe we can consider the performance more. Perhaps we can avoid traversing twice. Using a callback in the runGitDiffTree function might be more efficient, eliminating the need to create a slice of DiffTreeRecord before transforming it into another slice.