From 0816e807c9f9e29239f905856cf25d205a562bad Mon Sep 17 00:00:00 2001
From: Luke Shumaker <lukeshu@parabola.nu>
Date: Sat, 1 May 2021 15:41:23 -0600
Subject: That's what Commit.Force was for!

---
 fi-prune-empty2/main.go   |  5 ++++-
 fi-prune-empty2/prune.go  |  5 +++++
 fi-prune-empty2/stream.go | 40 +++++++++++++++++++++++++++++++---------
 3 files changed, 40 insertions(+), 10 deletions(-)

diff --git a/fi-prune-empty2/main.go b/fi-prune-empty2/main.go
index 0278a66..dd2594d 100644
--- a/fi-prune-empty2/main.go
+++ b/fi-prune-empty2/main.go
@@ -31,6 +31,8 @@ type Args struct {
 	help   bool
 	srcdir string
 
+	allowExcludedParents bool
+
 	pruneEmpty       PruneArg
 	pruneFastForward PruneArg
 	existingReplace  ExistingReplaceArg
@@ -44,6 +46,7 @@ func main() {
 
 	argparser.BoolVarP(&args.help, "help", "h", false, "Show this message")
 	argparser.StringVar(&args.srcdir, "srcdir", ".", "Path to the source git repository; this is required for '--prune-empty=auto' and '--prune-fastforward=auto'")
+	argparser.BoolVar(&args.allowExcludedParents, "allow-excluded-parents", false, "Whether to allow excluded parents to be referenced by commit-hash rather than by mark")
 
 	args.pruneEmpty = PruneAuto
 	argparser.Var(&args.pruneEmpty, "prune-empty", "Whether to prune empty commits; 'auto' means only prune commits which have become empty but are not empty in the --srcdir repo with GIT_NO_REPLACE_OBJECTS")
@@ -86,7 +89,7 @@ func main() {
 	frontend := libfastimport.NewFrontend(os.Stdin, os.Stdin, nil)
 	backend := libfastimport.NewBackend(os.Stdout, os.Stdout, nil)
 
-	filter := NewHandler(backend, NewDriver(args, backend))
+	filter := NewHandler(backend, NewDriver(args, backend), args.allowExcludedParents)
 	if err := fiutil.RunHandler(frontend, filter); err != nil {
 		fmt.Fprintf(os.Stderr, "%s: error: %v\n", os.Args[0], err)
 		os.Exit(1)
diff --git a/fi-prune-empty2/prune.go b/fi-prune-empty2/prune.go
index e3181b2..517f9c5 100644
--- a/fi-prune-empty2/prune.go
+++ b/fi-prune-empty2/prune.go
@@ -291,6 +291,11 @@ func (p *Pruner) isFastForward(commit Commit) (bool, error) {
 }
 
 func (p *Pruner) shouldPrune(commit Commit) (bool, error) {
+	if commit.ExcludedParents {
+		// If there are any excluded parents, then we can't
+		// reason about it.  Keep the commit.
+		return false, nil
+	}
 	switch p.pruneEmpty {
 	case PruneAlways:
 		isEmpty, err := p.isEmpty(commit)
diff --git a/fi-prune-empty2/stream.go b/fi-prune-empty2/stream.go
index be36d54..cadaf8b 100644
--- a/fi-prune-empty2/stream.go
+++ b/fi-prune-empty2/stream.go
@@ -75,6 +75,8 @@ type Commit struct {
 	OriginalOID Hash
 	Parents     []Mark
 	Tree        Tree
+
+	ExcludedParents bool
 }
 
 type Driver interface {
@@ -123,6 +125,8 @@ type Handler struct {
 	backend *libfastimport.Backend
 	driver  Driver
 
+	allowExcludedParents bool
+
 	// current refs
 	refs map[string]Mark
 
@@ -136,11 +140,13 @@ type Handler struct {
 	beg        time.Time
 }
 
-func NewHandler(backend *libfastimport.Backend, driver Driver) *Handler {
+func NewHandler(backend *libfastimport.Backend, driver Driver, allowExcludedParents bool) *Handler {
 	return &Handler{
 		backend: backend,
 		driver:  driver,
 
+		allowExcludedParents: allowExcludedParents,
+
 		// current refs
 		refs: map[string]Mark{},
 
@@ -214,7 +220,11 @@ func (h *Handler) CmdCommitEnd(cmd libfastimport.CmdCommitEnd) error {
 		return parents, nil
 	}()
 	if err != nil {
-		return err
+		if h.allowExcludedParents {
+			cmt.ExcludedParents = true
+		} else {
+			return err
+		}
 	}
 
 	sort.Stable(h.commitFile)
@@ -255,14 +265,26 @@ func (h *Handler) CmdCommitEnd(cmd libfastimport.CmdCommitEnd) error {
 
 		// apply the mutations from ProcessCommit to
 		// h.commitMeta
-		if len(cmtptr.Parents) == 0 {
-			h.commitMeta.From = EmptyHash
-			h.commitMeta.Merge = nil
+		if cmt.ExcludedParents {
+			h.commitMeta.From = h.driver.FixCommitIsh(h.commitMeta.From)
+			merge := make([]string, 0, len(h.commitMeta.Merge))
+			for i := range h.commitMeta.Merge {
+				fixed := h.driver.FixCommitIsh(h.commitMeta.Merge[i])
+				if fixed != "" {
+					merge = append(merge, fixed)
+				}
+			}
+			h.commitMeta.Merge = merge
 		} else {
-			h.commitMeta.From = fmt.Sprintf(":%d", cmtptr.Parents[0])
-			h.commitMeta.Merge = nil
-			for _, merge := range cmtptr.Parents[1:] {
-				h.commitMeta.Merge = append(h.commitMeta.Merge, fmt.Sprintf(":%d", merge))
+			if len(cmtptr.Parents) == 0 {
+				h.commitMeta.From = EmptyHash
+				h.commitMeta.Merge = nil
+			} else {
+				h.commitMeta.From = fmt.Sprintf(":%d", cmtptr.Parents[0])
+				h.commitMeta.Merge = nil
+				for _, merge := range cmtptr.Parents[1:] {
+					h.commitMeta.Merge = append(h.commitMeta.Merge, fmt.Sprintf(":%d", merge))
+				}
 			}
 		}
 
-- 
cgit v1.2.2