From af0b9a0412531b44b954494c3d132392f194022a Mon Sep 17 00:00:00 2001
From: Matt Moore <mattmoor@google.com>
Date: Thu, 15 Aug 2019 14:55:43 +0000
Subject: [PATCH] Add support for resolving refs, when linked.

With https://github.com/google/ko/pull/73 we can link the Git ref information
into images with:
```
ln -r -s .git/refs ./cmd/foo/kodata
```

If the changeset package gets a `ref: <ref>` entry, it attempts to read that
file from `KO_DATA_PATH` next, which lets the changeset work much more effectively.
---
 changeset/commit.go                             | 15 +++++++++++----
 changeset/commit_test.go                        | 17 +++++++++++++----
 changeset/testdata/garbage/HEAD                 |  1 +
 changeset/testdata/with-refs/HEAD               |  1 +
 .../testdata/with-refs/refs/heads/branch-name   |  1 +
 5 files changed, 27 insertions(+), 8 deletions(-)
 create mode 100644 changeset/testdata/garbage/HEAD
 create mode 100644 changeset/testdata/with-refs/HEAD
 create mode 100644 changeset/testdata/with-refs/refs/heads/branch-name

diff --git a/changeset/commit.go b/changeset/commit.go
index 77ed709321..5d2bf5398a 100644
--- a/changeset/commit.go
+++ b/changeset/commit.go
@@ -42,11 +42,18 @@ func Get() (string, error) {
 		return "", err
 	}
 	commitID := strings.TrimSpace(string(data))
-	if !commitIDRE.MatchString(commitID) {
-		err := fmt.Errorf("%q is not a valid GitHub commit ID", commitID)
-		return "", err
+	if strings.HasPrefix(commitID, "ref: ") {
+		refName := commitID[len("ref: "):]
+		data, err := readFileFromKoData(refName)
+		if err != nil {
+			return "", err
+		}
+		commitID = strings.TrimSpace(string(data))
+	}
+	if commitIDRE.MatchString(commitID) {
+		return commitID[:7], nil
 	}
-	return string(commitID[0:7]), nil
+	return "", fmt.Errorf("%q is not a valid GitHub commit ID", commitID)
 }
 
 // readFileFromKoData tries to read data as string from the file with given name
diff --git a/changeset/commit_test.go b/changeset/commit_test.go
index 85076500e0..00257834f0 100644
--- a/changeset/commit_test.go
+++ b/changeset/commit_test.go
@@ -24,8 +24,8 @@ import (
 )
 
 const (
-	nonCommittedHeadContext = "ref: refs/heads/non_committed_branch"
-	testCommitID            = "a2d1bdf"
+	nonCommittedHeadRef = "refs/heads/non_committed_branch"
+	testCommitID        = "a2d1bdf"
 )
 
 func TestReadFile(t *testing.T) {
@@ -41,10 +41,19 @@ func TestReadFile(t *testing.T) {
 		koDataPath: "testdata",
 		want:       testCommitID,
 	}, {
-		name:       "non committed branch",
+		name:       "no refs link",
 		koDataPath: "testdata/noncommitted",
 		wantErr:    true,
-		err:        fmt.Errorf("%q is not a valid GitHub commit ID", nonCommittedHeadContext),
+		err:        fmt.Errorf("open testdata/noncommitted/%s: no such file or directory", nonCommittedHeadRef),
+	}, {
+		name:       "with refs link",
+		koDataPath: "testdata/with-refs",
+		want:       testCommitID,
+	}, {
+		name:       "with bad content",
+		koDataPath: "testdata/garbage",
+		wantErr:    true,
+		err:        fmt.Errorf(`"garbage contents" is not a valid GitHub commit ID`),
 	}, {
 		name:       "KO_DATA_PATH is empty",
 		koDataPath: "",
diff --git a/changeset/testdata/garbage/HEAD b/changeset/testdata/garbage/HEAD
new file mode 100644
index 0000000000..0717e55530
--- /dev/null
+++ b/changeset/testdata/garbage/HEAD
@@ -0,0 +1 @@
+garbage contents
\ No newline at end of file
diff --git a/changeset/testdata/with-refs/HEAD b/changeset/testdata/with-refs/HEAD
new file mode 100644
index 0000000000..b86b48fd85
--- /dev/null
+++ b/changeset/testdata/with-refs/HEAD
@@ -0,0 +1 @@
+ref: refs/heads/branch-name
\ No newline at end of file
diff --git a/changeset/testdata/with-refs/refs/heads/branch-name b/changeset/testdata/with-refs/refs/heads/branch-name
new file mode 100644
index 0000000000..58b38ebaed
--- /dev/null
+++ b/changeset/testdata/with-refs/refs/heads/branch-name
@@ -0,0 +1 @@
+a2d1bdfe929516d7da141aef68631a7ee6941b2d