Add support for SHA-256 Git commit IDs

This also adds a few (mostly edge-case) tests for the `gitutil.IsCommitSHA` function.

Signed-off-by: Tianon Gravi <[email protected]>

util/gitutil/git_commit.go

@@ -1,7 +1,7 @@
 package gitutil
 
 func IsCommitSHA(str string) bool {
-	if len(str) != 40 {
+	if l := len(str); l != 40 && l != 64 {
 		return false
 	}
 

util/gitutil/git_commit_test.go

@@ -0,0 +1,35 @@
+package gitutil
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestIsCommitSHA(t *testing.T) {
+	for truthy, commits := range map[bool][]string{
+		true: {
+			"01234567890abcdef01234567890abcdef012345", // 40 valid characters (SHA-1)
+			"01234567890abcdef01234567890abcdef01234567890abcdef01234567890ab", // 64 valid characters (SHA-256)
+		},
+		false: {
+			"", // empty string
+			"abcdef", // too short
+
+			"123456789012345678901234567890123456789", // 39 valid characters
+			"!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!", // 40 invalid characters
+			"12345678901234567890123456789012345678901", // 41 valid characters
+
+			"01234567890abcdef01234567890abcdef01234567890abcdef01234567890a", // 63 valid characters
+			"zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz", // 64 invalid characters
+			"01234567890abcdef01234567890abcdef01234567890abcdef01234567890abc", // 65 valid characters
+		},
+	} {
+		for _, commit := range commits {
+			t.Run(fmt.Sprintf("%t/%q", truthy, commit), func(t *testing.T) {
+				assert.Equal(t, truthy, IsCommitSHA(commit))
+			})
+		}
+	}
+}