WIP Add config pagerForStaging

Problems:
- sometimes the wrapping is off; I suspect Decolorize is missing some cases
- in the patch building panel, only shows the formatted diff as long as nothing
  has been staged, because then it wants to color the line starts of the
  included lines
- with delta, selection is almost invisible because we are only changing the
  background color, but delta colors the background too (diff-so-fancy doesn't)

docs/Config.md

@@ -280,6 +280,11 @@ git:
     # ydiff -p cat -s --wrap --width={{columnWidth}}
     pager: ""
 
+    # e.g.
+    # delta --dark --paging=never --color-only
+    # diff-so-fancy --patch
+    pagerForStaging: ""
+
     # If 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).
     useConfig: false
 

pkg/config/user_config.go

@@ -284,6 +284,15 @@ func (PagerType) JSONSchemaExtend(schema *jsonschema.Schema) {
 	}
 }
 
+type PagerForStagingType string
+
+func (PagerForStagingType) JSONSchemaExtend(schema *jsonschema.Schema) {
+	schema.Examples = []any{
+		"delta --dark --paging=never --color-only",
+		"diff-so-fancy --patch",
+	}
+}
+
 type PagingConfig struct {
 	// Value of the --color arg in the git diff command. Some pagers want this to be set to 'always' and some want it set to 'never'
 	ColorArg string `yaml:"colorArg" jsonschema:"enum=always,enum=never"`
@@ -292,6 +301,10 @@ type PagingConfig struct {
 	// delta --dark --paging=never
 	// ydiff -p cat -s --wrap --width={{columnWidth}}
 	Pager PagerType `yaml:"pager"`
+	// e.g.
+	// delta --dark --paging=never --color-only
+	// diff-so-fancy --patch
+	PagerForStaging PagerForStagingType `yaml:"pagerForStaging"`
 	// If 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).
 	UseConfig bool `yaml:"useConfig"`
 	// e.g. 'difft --color=always'

pkg/gui/controllers/helpers/patch_building_helper.go

@@ -91,7 +91,7 @@ func (self *PatchBuildingHelper) RefreshPatchBuildingPanel(opts types.OnFocusOpt
 
 	oldState := context.GetState()
 
-	state := patch_exploring.NewState(diff, selectedLineIdx, context.GetView(), oldState)
+	state := patch_exploring.NewState(diff, selectedLineIdx, context.GetView(), oldState, string(self.c.UserConfig().Git.Paging.PagerForStaging))
 	context.SetState(state)
 	if state == nil {
 		self.Escape()

pkg/gui/controllers/helpers/staging_helper.go

@@ -62,12 +62,14 @@ func (self *StagingHelper) RefreshStagingPanel(focusOpts types.OnFocusOpts) {
 	mainContext.GetMutex().Lock()
 	secondaryContext.GetMutex().Lock()
 
+	pagerCommand := string(self.c.UserConfig().Git.Paging.PagerForStaging)
+
 	mainContext.SetState(
-		patch_exploring.NewState(mainDiff, mainSelectedLineIdx, mainContext.GetView(), mainContext.GetState()),
+		patch_exploring.NewState(mainDiff, mainSelectedLineIdx, mainContext.GetView(), mainContext.GetState(), pagerCommand),
 	)
 
 	secondaryContext.SetState(
-		patch_exploring.NewState(secondaryDiff, secondarySelectedLineIdx, secondaryContext.GetView(), secondaryContext.GetState()),
+		patch_exploring.NewState(secondaryDiff, secondarySelectedLineIdx, secondaryContext.GetView(), secondaryContext.GetState(), pagerCommand),
 	)
 
 	mainState := mainContext.GetState()

pkg/gui/patch_exploring/state.go

@@ -1,12 +1,16 @@
 package patch_exploring
 
 import (
+	"bytes"
+	"io"
+	"os/exec"
 	"strings"
 
 	"github.com/jesseduffield/generics/set"
 	"github.com/jesseduffield/gocui"
 	"github.com/jesseduffield/lazygit/pkg/commands/patch"
 	"github.com/jesseduffield/lazygit/pkg/utils"
+	"github.com/mgutz/str"
 )
 
 // State represents the current state of the patch explorer context i.e. when
@@ -20,6 +24,7 @@ type State struct {
 	// Otherwise, we cancel the range when we move up or down.
 	rangeIsSticky bool
 	diff          string
+	diffFromPager string
 	patch         *patch.Patch
 	selectMode    selectMode
 
@@ -38,7 +43,7 @@ const (
 	HUNK
 )
 
-func NewState(diff string, selectedLineIdx int, view *gocui.View, oldState *State) *State {
+func NewState(diff string, selectedLineIdx int, view *gocui.View, oldState *State, pagerCommand string) *State {
 	if oldState != nil && diff == oldState.diff && selectedLineIdx == -1 {
 		// if we're here then we can return the old state. If selectedLineIdx was not -1
 		// then that would mean we were trying to click and potentially drag a range, which
@@ -52,7 +57,13 @@ func NewState(diff string, selectedLineIdx int, view *gocui.View, oldState *Stat
 		return nil
 	}
 
-	viewLineIndices, patchLineIndices := wrapPatchLines(diff, view)
+	diffFromPager := formatDiffForStaging(diff, pagerCommand)
+	diffToWrap := diff
+	if len(diffFromPager) > 0 {
+		diffToWrap = utils.Decolorise(diffFromPager)
+	}
+
+	viewLineIndices, patchLineIndices := wrapPatchLines(diffToWrap, view)
 
 	rangeStartLineIdx := 0
 	if oldState != nil {
@@ -85,11 +96,37 @@ func NewState(diff string, selectedLineIdx int, view *gocui.View, oldState *Stat
 		rangeStartLineIdx: rangeStartLineIdx,
 		rangeIsSticky:     false,
 		diff:              diff,
+		diffFromPager:     diffFromPager,
 		viewLineIndices:   viewLineIndices,
 		patchLineIndices:  patchLineIndices,
 	}
 }
 
+func formatDiffForStaging(diff string, pagerCommand string) string {
+	if len(pagerCommand) == 0 {
+		return ""
+	}
+
+	args := str.ToArgv(pagerCommand)
+	cmd := exec.Command(args[0], args[1:]...)
+	var stdout bytes.Buffer
+	cmd.Stdout = &stdout
+	cmd.Stderr = io.Discard
+	cmd.Stdin = strings.NewReader(diff)
+
+	err := cmd.Run()
+	if err != nil {
+		// TODO report error somehow
+		return ""
+	}
+	diffFromPager := stdout.String()
+	if len(strings.Split(diffFromPager, "\n")) != len(strings.Split(diff, "\n")) {
+		// TODO report error somehow
+		return ""
+	}
+	return diffFromPager
+}
+
 func (s *State) OnViewWidthChanged(view *gocui.View) {
 	if !view.Wrap {
 		return
@@ -294,6 +331,9 @@ func (s *State) AdjustSelectedLineIdx(change int) {
 }
 
 func (s *State) RenderForLineIndices(includedLineIndices []int) string {
+	if includedLineIndices == nil && len(s.diffFromPager) > 0 {
+		return s.diffFromPager
+	}
 	includedLineIndicesSet := set.NewFromSlice(includedLineIndices)
 	return s.patch.FormatView(patch.FormatViewOpts{
 		IncLineIndices: includedLineIndicesSet,

schema/config.json

@@ -1548,6 +1548,15 @@
             "ydiff -p cat -s --wrap --width={{columnWidth}}"
           ]
         },
+        "pagerForStaging": {
+          "type": "string",
+          "description": "e.g.\ndelta --dark --paging=never --color-only\ndiff-so-fancy --patch",
+          "default": "",
+          "examples": [
+            "delta --dark --paging=never --color-only",
+            "diff-so-fancy --patch"
+          ]
+        },
         "useConfig": {
           "type": "boolean",
           "description": "If 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).",