[repo-assist] fix(diff): add --no-pager and package header to git diff (#1243) (#2905)

* fix(diff): add --no-pager and package header to git diff

Previously, each package's diff was shown via a separate `git diff`
invocation with Show(), allowing git to invoke its own pager (e.g. less)
independently for each package. This caused inconsistent pagination:
large diffs opened a pager, small diffs scrolled past in the terminal.

Changes:
- Add --no-pager flag to git diff so git doesn't open its own pager
  per package; all diffs now stream consistently to stdout.
- Print a package name header before each diff so users can easily
  identify which package each diff belongs to when reviewing multiple
  packages.

Closes #1243

* bunch up diffs and render in one go

Co-authored-by: Jo Garnier <me@jguer.space>

README.md

@@ -119,11 +119,12 @@ pacman -S --needed git base-devel yay
   Make sure you have the `Color` option in your `/etc/pacman.conf`
   (see issue [#123](https://github.com/Jguer/yay/issues/123)).
 
-- **Sometimes diffs are printed to the terminal, and other times they are paged via less. How do I fix this?**
+- **How do I change the pager used for PKGBUILD diffs?**
 
-  yay uses `git diff` to display diffs, which by default tells less not to
-  page if the output can fit into one terminal length. This behavior can be
-  overridden by exporting your own flags (`export LESS=SRX`).
+  Diffs for all selected packages are collected and shown in a single pager
+  session. Set `pager` in `config.json` or `yay.opt.pager` in `init.lua`, or
+  set `PAGER` to override the default (`less`, or `cat` if less is unavailable).
+  Example: `yay.opt.pager = "delta"` or `export PAGER=less`.
 
 - **yay is not asking me to edit PKGBUILDS, and I don't like the diff menu! What can I do?**
 

doc/init.lua

@@ -9,6 +9,7 @@ yay.opt.aurrpcurl = ""
 yay.opt.build_dir = os.getenv("HOME") .. "/.cache/yay"
 yay.opt.editor = os.getenv("EDITOR") or os.getenv("VISUAL") or "vi"
 yay.opt.editor_flags = ""
+yay.opt.pager = os.getenv("PAGER") or ""
 yay.opt.makepkg_bin = "makepkg"
 yay.opt.makepkg_conf = ""
 yay.opt.pacman_bin = "pacman"

doc/lua.md

@@ -66,7 +66,7 @@ startup and reports the offending keys/values so misconfigurations fail fast.
 
 **Strings**
 
-`aururl`, `aurrpcurl`, `build_dir`, `editor`, `editor_flags`, `makepkg_bin`,
+`aururl`, `aurrpcurl`, `build_dir`, `editor`, `editor_flags`, `pager`, `makepkg_bin`,
 `makepkg_conf`, `pacman_bin`, `pacman_conf`, `redownload`, `rebuild`, `git_bin`,
 `gpg_bin`, `gpg_flags`, `mflags`, `sort_by`, `search_by`, `git_flags`,
 `remove_make`, `sudo_bin`, `sudo_flags`

doc/yay.8

@@ -307,9 +307,10 @@ using '--cleanmenu=false' on the command line
 Show the diff menu. This menu gives you the option to view diffs from
 build files before building.
 
-Diffs are shown via \fBgit diff\fR which uses
-less by default. This behaviour can be changed via git's config, the
-\fB$GIT_PAGER\fR or \fB$PAGER\fR environment variables.
+Diffs for all selected packages are collected and shown through a single
+pager. The pager is taken from the \fBpager\fR config option (also settable
+via Lua as \fByay.opt.pager\fR), then \fB$PAGER\fR, then \fBless\fR (or
+\fBcat\fR if less is unavailable).
 
 .TP
 .B \-\-editmenu
@@ -540,6 +541,11 @@ Overridden by \-\-builddir.
 When editor is not configured, use these variables to pick what editor
 to use when editing PKGBUILDS.
 
+.TP
+.B PAGER
+When pager is not configured, use this variable when showing PKGBUILD diffs.
+If unset, yay uses \fBless\fR when available, otherwise \fBcat\fR.
+
 .SH FILES
 .TP
 .B CONFIG DIRECTORY

pkg/menus/diff_menu.go

@@ -23,9 +23,35 @@ const (
 )
 
 func showPkgbuildDiffs(ctx context.Context, cmdBuilder exe.ICmdBuilder, logger *text.Logger,
-	pkgbuildDirs map[string]string, bases []string,
+	pkgbuildDirs map[string]string, bases []string, pagerConfig string,
 ) error {
-	var errs []error
+	combined, errs := collectPkgbuildDiffs(ctx, cmdBuilder, logger, pkgbuildDirs, bases)
+	if combined == "" {
+		return errors.Join(errs...)
+	}
+
+	if !isStdoutTerminal() {
+		logger.Print(combined)
+
+		return errors.Join(errs...)
+	}
+
+	if err := runPager(ctx, combined, pagerConfig); err != nil {
+		errs = append(errs, err)
+	}
+
+	return errors.Join(errs...)
+}
+
+// collectPkgbuildDiffs captures each selected package's git diff with --no-pager
+// and joins them with package headers into one buffer for a single pager session.
+func collectPkgbuildDiffs(ctx context.Context, cmdBuilder exe.ICmdBuilder, logger *text.Logger,
+	pkgbuildDirs map[string]string, bases []string,
+) (string, []error) {
+	var (
+		errs []error
+		buf  strings.Builder
+	)
 
 	for _, pkg := range bases {
 		dir := pkgbuildDirs[pkg]
@@ -53,7 +79,7 @@ func showPkgbuildDiffs(ctx context.Context, cmdBuilder exe.ICmdBuilder, logger *
 		}
 
 		args := []string{
-			"diff",
+			"--no-pager", "diff",
 			start + "..HEAD@{upstream}", "--src-prefix",
 			dir + "/", "--dst-prefix", dir + "/", "--", ".", ":(exclude).SRCINFO",
 		}
@@ -63,10 +89,24 @@ func showPkgbuildDiffs(ctx context.Context, cmdBuilder exe.ICmdBuilder, logger *
 			args = append(args, "--color=never")
 		}
 
-		_ = cmdBuilder.Show(cmdBuilder.BuildGitCmd(ctx, dir, args...))
+		stdout, stderr, err := cmdBuilder.Capture(cmdBuilder.BuildGitCmd(ctx, dir, args...))
+		if err != nil {
+			errs = append(errs, fmt.Errorf("%s%w", stderr, err))
+
+			continue
+		}
+
+		if stdout == "" {
+			continue
+		}
+
+		buf.WriteString(logger.SprintOperationInfo(gotext.Get("Showing diff for %s", text.Bold(pkg))))
+		buf.WriteByte('\n')
+		buf.WriteString(stdout)
+		buf.WriteString("\n\n")
 	}
 
-	return errors.Join(errs...)
+	return buf.String(), errs
 }
 
 // Check whether or not a diff exists between the last reviewed diff and
@@ -163,7 +203,7 @@ func DiffFn(ctx context.Context, run *runtime.Runtime, w io.Writer,
 		return errMenu
 	}
 
-	if errD := showPkgbuildDiffs(ctx, run.CmdBuilder, run.Logger, pkgbuildDirsByBase, toDiff); errD != nil {
+	if errD := showPkgbuildDiffs(ctx, run.CmdBuilder, run.Logger, pkgbuildDirsByBase, toDiff, run.Cfg.Pager); errD != nil {
 		return errD
 	}
 

pkg/menus/pager.go

@@ -0,0 +1,54 @@
+package menus
+
+import (
+	"context"
+	"os"
+	"os/exec"
+	"strings"
+
+	"golang.org/x/term"
+)
+
+// runPager pages content through a single pager process. Overridable in tests.
+var runPager = pageThroughPager
+
+// isStdoutTerminal reports whether stdout is a terminal. Overridable in tests.
+var isStdoutTerminal = func() bool {
+	return term.IsTerminal(int(os.Stdout.Fd()))
+}
+
+// resolvePager returns the pager command string.
+// Priority: config pager → PAGER → less → cat.
+func resolvePager(pagerConfig string) string {
+	if pagerConfig != "" {
+		return pagerConfig
+	}
+
+	if pager := os.Getenv("PAGER"); pager != "" {
+		return pager
+	}
+
+	if _, err := exec.LookPath("less"); err == nil {
+		return "less"
+	}
+
+	return "cat"
+}
+
+// pageThroughPager runs the configured pager with content on stdin.
+// The pager command is user-controlled (config / $PAGER), same model as $EDITOR.
+func pageThroughPager(ctx context.Context, content, pagerConfig string) error {
+	pager := resolvePager(pagerConfig)
+	cmd := exec.CommandContext(ctx, "sh", "-c", pager)
+	cmd.Stdin = strings.NewReader(content)
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	cmd.Env = os.Environ()
+
+	if os.Getenv("LESS") == "" {
+		// S: chop long lines; R: raw ANSI; X: no termcap init; F: quit if one screen
+		cmd.Env = append(cmd.Env, "LESS=SRXF")
+	}
+
+	return cmd.Run()
+}

pkg/menus/pager_test.go

@@ -0,0 +1,127 @@
+//go:build !integration
+
+package menus
+
+import (
+	"bytes"
+	"context"
+	"os/exec"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"github.com/Jguer/yay/v13/pkg/text"
+)
+
+func TestResolvePager(t *testing.T) {
+	// Not parallel: t.Setenv cannot be used after t.Parallel.
+	tests := []struct {
+		name        string
+		pagerConfig string
+		pager       string
+		want        string
+	}{
+		{name: "config wins", pagerConfig: "delta", pager: "less", want: "delta"},
+		{name: "PAGER when config empty", pagerConfig: "", pager: "most", want: "most"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Setenv("PAGER", tt.pager)
+
+			assert.Equal(t, tt.want, resolvePager(tt.pagerConfig))
+		})
+	}
+}
+
+func TestCollectPkgbuildDiffs(t *testing.T) {
+	t.Parallel()
+
+	var warnOut bytes.Buffer
+	logger := text.NewLogger(&bytes.Buffer{}, &warnOut, strings.NewReader(""), false, "test")
+
+	builder := &fakeMenusCmdBuilder{
+		captureFn: func(cmd *exec.Cmd) (string, string, error) {
+			joined := strings.Join(cmd.Args, " ")
+
+			switch {
+			case strings.Contains(joined, "--quiet --verify AUR_SEEN"):
+				return "", "", nil
+			case strings.Contains(joined, "rev-parse AUR_SEEN HEAD@{upstream}"):
+				return "aaa\nbbb\n", "", nil
+			case strings.Contains(joined, "rev-parse AUR_SEEN"):
+				return "aaa\n", "", nil
+			case strings.Contains(joined, "--no-pager diff"):
+				require.Contains(t, joined, "--no-pager")
+				pkg := "alpha"
+				if strings.Contains(joined, "beta/") {
+					pkg = "beta"
+				}
+
+				return "diff for " + pkg, "", nil
+			default:
+				t.Fatalf("unexpected git args: %s", joined)
+
+				return "", "", nil
+			}
+		},
+	}
+
+	dirs := map[string]string{
+		"alpha": "/tmp/alpha",
+		"beta":  "/tmp/beta",
+	}
+
+	out, errs := collectPkgbuildDiffs(context.Background(), builder, logger, dirs, []string{"alpha", "beta"})
+	require.Empty(t, errs)
+	require.Contains(t, out, "Showing diff for")
+	require.Contains(t, out, "diff for alpha")
+	require.Contains(t, out, "diff for beta")
+	// Headers for both packages appear before their diffs in one buffer.
+	alphaIdx := strings.Index(out, "diff for alpha")
+	betaIdx := strings.Index(out, "diff for beta")
+	require.Positive(t, alphaIdx)
+	require.Greater(t, betaIdx, alphaIdx)
+}
+
+func TestShowPkgbuildDiffsPagesOnce(t *testing.T) {
+	t.Parallel()
+
+	var paged strings.Builder
+	origRunPager := runPager
+	origIsTTY := isStdoutTerminal
+	t.Cleanup(func() {
+		runPager = origRunPager
+		isStdoutTerminal = origIsTTY
+	})
+
+	isStdoutTerminal = func() bool { return true }
+	runPager = func(_ context.Context, content, _ string) error {
+		paged.WriteString(content)
+
+		return nil
+	}
+
+	logger := text.NewLogger(&bytes.Buffer{}, &bytes.Buffer{}, strings.NewReader(""), false, "test")
+	builder := &fakeMenusCmdBuilder{
+		captureFn: func(cmd *exec.Cmd) (string, string, error) {
+			joined := strings.Join(cmd.Args, " ")
+			switch {
+			case strings.Contains(joined, "--quiet --verify AUR_SEEN"):
+				return "", "", exec.ErrNotFound // no AUR_SEEN → empty tree, always show
+			case strings.Contains(joined, "--no-pager diff"):
+				return "+++ changed", "", nil
+			default:
+				return "", "", nil
+			}
+		},
+	}
+
+	err := showPkgbuildDiffs(context.Background(), builder, logger,
+		map[string]string{"pkg": "/tmp/pkg"}, []string{"pkg"}, "")
+	require.NoError(t, err)
+	require.Contains(t, paged.String(), "+++ changed")
+	require.Contains(t, paged.String(), "Showing diff for")
+}

pkg/settings/config.go

@@ -28,6 +28,7 @@ type Configuration struct {
 	BuildDir               string `json:"buildDir" lua:"build_dir"`
 	Editor                 string `json:"editor" lua:"editor"`
 	EditorFlags            string `json:"editorflags" lua:"editor_flags"`
+	Pager                  string `json:"pager" lua:"pager"`
 	MakepkgBin             string `json:"makepkgbin" lua:"makepkg_bin"`
 	MakepkgConf            string `json:"makepkgconf" lua:"makepkg_conf"`
 	PacmanBin              string `json:"pacmanbin" lua:"pacman_bin"`
@@ -115,6 +116,7 @@ func (c *Configuration) expandEnv() {
 	c.BuildDir = expandEnvOrHome(c.BuildDir)
 	c.Editor = expandEnvOrHome(c.Editor)
 	c.EditorFlags = os.ExpandEnv(c.EditorFlags)
+	c.Pager = os.ExpandEnv(c.Pager)
 	c.MakepkgBin = expandEnvOrHome(c.MakepkgBin)
 	c.MakepkgConf = expandEnvOrHome(c.MakepkgConf)
 	c.PacmanBin = expandEnvOrHome(c.PacmanBin)
@@ -196,6 +198,7 @@ func DefaultConfig(version string) *Configuration {
 		KeepSrc:                false,
 		Editor:                 "",
 		EditorFlags:            "",
+		Pager:                  "",
 		Devel:                  false,
 		MakepkgBin:             "makepkg",
 		MakepkgConf:            "",