test(repo sync): verify squash-merge behavior (#535)

Adds a test that squash-merges a shamhub PR
and verifies that repo sync behaves as expected.

internal/forge/shamhub/cli.go

@@ -136,6 +136,7 @@ func (c *Cmd) Run(ts *testscript.TestScript, neg bool, args []string) {
 		}
 
 		prune := flag.Bool("prune", false, "prune the branch after merging")
+		squash := flag.Bool("squash", false, "squash-merge the commit")
 		ts.Check(flag.Parse(args))
 		args = flag.Args()
 		if len(args) != 2 {
@@ -158,6 +159,7 @@ func (c *Cmd) Run(ts *testscript.TestScript, neg bool, args []string) {
 			Repo:         repo,
 			Number:       pr,
 			DeleteBranch: *prune,
+			Squash:       *squash,
 		}
 		if at := ts.Getenv("GIT_COMMITTER_DATE"); at != "" {
 			t, err := time.Parse(time.RFC3339, at)

internal/forge/shamhub/merge.go

@@ -105,7 +105,10 @@ type MergeChangeRequest struct {
 	// should be deleted after the merge.
 	DeleteBranch bool
 
-	// TODO: option to use squash commit
+	// Squash requests that the CR be merged
+	// as a single squashed commit with the PR subject/body
+	// instead of a merge commit.
+	Squash bool
 }
 
 // MergeChange merges an open change against this forge.
@@ -180,14 +183,22 @@ func (sh *ShamHub) MergeChange(req MergeChangeRequest) error {
 		logw, flush := ioutil.LogWriter(sh.log, log.DebugLevel)
 		defer flush()
 
-		msg := fmt.Sprintf("Merge change #%d", req.Number)
-		cmd := exec.Command(sh.gitExe,
-			"commit-tree",
-			"-p", sh.changes[changeIdx].Base,
-			"-p", sh.changes[changeIdx].Head,
-			"-m", msg,
-			tree,
-		)
+		change := sh.changes[changeIdx]
+
+		var msg string
+		args := []string{"commit-tree", "-p", change.Base}
+		if req.Squash {
+			msg = fmt.Sprintf("%s (#%d)\n\n%s",
+				change.Subject,
+				req.Number,
+				change.Body)
+		} else {
+			msg = fmt.Sprintf("Merge change #%d", req.Number)
+			args = append(args, "-p", change.Head)
+		}
+		args = append(args, "-m", msg, tree)
+
+		cmd := exec.Command(sh.gitExe, args...)
 		cmd.Dir = sh.repoDir(req.Owner, req.Repo)
 		cmd.Stderr = logw
 		cmd.Env = append(os.Environ(), commitEnv...)

testdata/script/repo_sync_squash_merged.txt

@@ -0,0 +1,99 @@
+# 'repo sync' handles squash-merged CRs correctly.
+
+as 'Test <[email protected]>'
+at '2024-12-28T18:14:15Z'
+
+# setup
+cd repo
+git init
+git commit --allow-empty -m 'Initial commit'
+
+# set up a fake GitHub remote
+shamhub init
+shamhub new origin alice/example.git
+shamhub register alice
+git push origin main
+
+env SHAMHUB_USERNAME=alice
+gs auth login
+
+# put all three changes in one commit
+git add feat1.txt
+gs bc -m 'Add feature 1'
+git add feat2.txt
+gs cc -m 'Add feature 2'
+git add feat3.txt
+gs cc -m 'Add feature 3'
+
+# Submit
+env ROBOT_INPUT=$WORK/robot.golden ROBOT_OUTPUT=$WORK/robot.actual
+gs branch submit
+cmp $WORK/robot.actual $WORK/robot.golden
+stderr 'Created #'
+
+shamhub dump change 1
+cmpenvJSON stdout $WORK/golden/pull.txt
+
+gs ll
+cmp stderr $WORK/golden/ll-before.txt
+
+shamhub merge --squash --prune alice/example 1
+gs repo sync
+stderr '#1 was merged'
+
+git log -n1 --pretty=%B
+cmp stdout $WORK/golden/final-commit-msg
+
+gs ll
+cmp stderr $WORK/golden/ll-after.txt
+
+-- repo/feat1.txt --
+feature 1
+-- repo/feat2.txt --
+feature 2
+-- repo/feat3.txt --
+feature 3
+
+-- robot.golden --
+===
+> Title: Add feature 1 
+> Short summary of the change
+"Add multiple features"
+===
+> Body: Press [e] to open mockedit or [enter/tab] to skip
+> Open your editor to write a detailed description of the change
+{"give": "Adds features 1, 2, and 3 in one PR."}
+===
+> Draft: [y/N]
+> Mark the change as a draft?
+false
+-- golden/pull.txt --
+{
+  "number": 1,
+  "html_url": "$SHAMHUB_URL/alice/example/change/1",
+  "state": "open",
+  "title": "Add multiple features",
+  "body": "Adds features 1, 2, and 3 in one PR.",
+  "base": {
+    "ref": "main",
+    "sha": "e41b284d1e80e3acba627274a80d94129ebdf8fd"
+  },
+  "head": {
+    "ref": "add-feature-1",
+    "sha": "a9548da1d2feba06f2bba402eb77adf27a9266e7"
+  }
+}
+
+-- golden/ll-before.txt --
+┏━■ add-feature-1 (#1) ◀
+┃   a9548da Add feature 3 (now)
+┃   bcb3a72 Add feature 2 (now)
+┃   4be7a61 Add feature 1 (now)
+main
+-- golden/ll-after.txt --
+main ◀
+-- golden/final-commit-msg --
+Add multiple features (#1)
+
+Adds features 1, 2, and 3 in one PR.
+