From 0a4e55f9a190b500835e10d187ca4f88a96917e2 Mon Sep 17 00:00:00 2001
From: Billy Keyes <commits@billykeyes.dev>
Date: Sun, 14 Jul 2024 23:44:16 -0400
Subject: [PATCH] Return preamble when a patch has no files (#46)

While empty patches with only a header were parsable, the parser
discarded the preamble content. This meant callers had to handle this
case specially. Now, if we reach the end of the input without finding a
file, Parse() returns the full content of the patch as the preamble.
---
 gitdiff/file_header.go          |  2 +-
 gitdiff/parser.go               |  6 +++---
 gitdiff/parser_test.go          | 18 ++++++++++++++++--
 gitdiff/testdata/no_files.patch |  8 ++++++++
 4 files changed, 28 insertions(+), 6 deletions(-)
 create mode 100644 gitdiff/testdata/no_files.patch

diff --git a/gitdiff/file_header.go b/gitdiff/file_header.go
index 77ceb5d..7ae4bc9 100644
--- a/gitdiff/file_header.go
+++ b/gitdiff/file_header.go
@@ -57,7 +57,7 @@ func (p *parser) ParseNextFileHeader() (*File, string, error) {
 			return nil, "", err
 		}
 	}
-	return nil, "", nil
+	return nil, preamble.String(), nil
 }
 
 func (p *parser) ParseGitFileHeader() (*File, error) {
diff --git a/gitdiff/parser.go b/gitdiff/parser.go
index d2b29cb..e8f8430 100644
--- a/gitdiff/parser.go
+++ b/gitdiff/parser.go
@@ -33,6 +33,9 @@ func Parse(r io.Reader) ([]*File, string, error) {
 		if err != nil {
 			return files, preamble, err
 		}
+		if len(files) == 0 {
+			preamble = pre
+		}
 		if file == nil {
 			break
 		}
@@ -50,9 +53,6 @@ func Parse(r io.Reader) ([]*File, string, error) {
 			}
 		}
 
-		if len(files) == 0 {
-			preamble = pre
-		}
 		files = append(files, file)
 	}
 
diff --git a/gitdiff/parser_test.go b/gitdiff/parser_test.go
index 30f59f4..15a5d67 100644
--- a/gitdiff/parser_test.go
+++ b/gitdiff/parser_test.go
@@ -281,8 +281,13 @@ this is another line
 --- could this be a header?
 nope, it's just some dashes
 `,
-			Output:   nil,
-			Preamble: "",
+			Output: nil,
+			Preamble: `
+this is a line
+this is another line
+--- could this be a header?
+nope, it's just some dashes
+`,
 		},
 		"detatchedFragmentLike": {
 			Input: `
@@ -290,6 +295,10 @@ a wild fragment appears?
 @@ -1,3 +1,4 ~1,5 @@
 `,
 			Output: nil,
+			Preamble: `
+a wild fragment appears?
+@@ -1,3 +1,4 ~1,5 @@
+`,
 		},
 		"detatchedFragment": {
 			Input: `
@@ -426,6 +435,11 @@ Date:   Tue Apr 2 22:55:40 2019 -0700
 			},
 			Preamble: textPreamble,
 		},
+		"noFiles": {
+			InputFile: "testdata/no_files.patch",
+			Output:    nil,
+			Preamble:  textPreamble,
+		},
 		"newBinaryFile": {
 			InputFile: "testdata/new_binary_file.patch",
 			Output: []*File{
diff --git a/gitdiff/testdata/no_files.patch b/gitdiff/testdata/no_files.patch
new file mode 100644
index 0000000..9eea12d
--- /dev/null
+++ b/gitdiff/testdata/no_files.patch
@@ -0,0 +1,8 @@
+commit 5d9790fec7d95aa223f3d20936340bf55ff3dcbe
+Author: Morton Haypenny <mhaypenny@example.com>
+Date:   Tue Apr 2 22:55:40 2019 -0700
+
+    A file with multiple fragments.
+
+    The content is arbitrary.
+