From 4127eeceb204b6b4d44b8fb9b3e8198aa6a23ea9 Mon Sep 17 00:00:00 2001
From: Anirudh Oppiliappan <anirudh@tangled.org>
Date: Wed, 18 Mar 2026 15:02:30 +0200
Subject: [PATCH] knotserver/git: compute changed files between commits and
 wire into workflow compiler

Signed-off-by: Anirudh Oppiliappan <anirudh@tangled.org>
---
 knotserver/git/diff.go | 48 ++++++++++++++++++++++++++++++++++++++++++
 knotserver/internal.go |  6 ++++++
 2 files changed, 54 insertions(+)

diff --git a/knotserver/git/diff.go b/knotserver/git/diff.go
index 38c761ab..46f4c0cd 100644
--- a/knotserver/git/diff.go
+++ b/knotserver/git/diff.go
@@ -158,6 +158,54 @@ func (g *GitRepo) formatSinglePatch(commit plumbing.Hash, extraArgs ...string) (
 	return raw, &formatPatch[0], nil
 }
 
+// ChangedFilesBetween returns the list of files changed between oldSha and newSha.
+// If oldSha is the zero hash (initial push), all files in newSha are returned.
+func (g *GitRepo) ChangedFilesBetween(oldSha, newSha string) ([]string, error) {
+	newCommit, err := g.ResolveRevision(newSha)
+	if err != nil {
+		return nil, err
+	}
+
+	if plumbing.NewHash(oldSha) == plumbing.ZeroHash {
+		tree, err := newCommit.Tree()
+		if err != nil {
+			return nil, err
+		}
+		var files []string
+		tree.Files().ForEach(func(f *object.File) error {
+			files = append(files, f.Name)
+			return nil
+		})
+		return files, nil
+	}
+
+	oldCommit, err := g.ResolveRevision(oldSha)
+	if err != nil {
+		return nil, err
+	}
+
+	dt, err := g.DiffTree(oldCommit, newCommit)
+	if err != nil {
+		return nil, err
+	}
+
+	seen := make(map[string]struct{})
+	for _, f := range dt.Diff {
+		if f.OldName != "" {
+			seen[f.OldName] = struct{}{}
+		}
+		if f.NewName != "" {
+			seen[f.NewName] = struct{}{}
+		}
+	}
+
+	files := make([]string, 0, len(seen))
+	for name := range seen {
+		files = append(files, name)
+	}
+	return files, nil
+}
+
 func (g *GitRepo) ResolveRevision(revStr string) (*object.Commit, error) {
 	rev, err := g.r.ResolveRevision(plumbing.Revision(revStr))
 	if err != nil {
diff --git a/knotserver/internal.go b/knotserver/internal.go
index 76f63260..625a72e8 100644
--- a/knotserver/internal.go
+++ b/knotserver/internal.go
@@ -385,12 +385,18 @@ func (h *InternalHandle) triggerPipeline(
 		DefaultBranch: defaultBranch,
 	}
 
+	changedFiles, err := gr.ChangedFilesBetween(line.OldSha.String(), line.NewSha.String())
+	if err != nil {
+		return fmt.Errorf("getting changed files: %w", err)
+	}
+
 	compiler := workflow.Compiler{
 		Trigger: tangled.Pipeline_TriggerMetadata{
 			Kind: string(workflow.TriggerKindPush),
 			Push: &trigger,
 			Repo: triggerRepo,
 		},
+		ChangedFiles: changedFiles,
 	}
 
 	cp := compiler.Compile(compiler.Parse(pipeline))
-- 
2.51.2