Remove "appendix" information from commit message (#19)

...when parsing emails, similar to `git am`.

Add a new field, `BodyAppendix` to PatchHeader.

Modify `scanMessageBody` to accept a boolean argument saying whether
to separate out the appendix or not.  Do this by keeping two string
builders, and having it switch to the appendix builder when it finds a
`---` line.

Handling the newlines at the end as expected requires moving things
around a bit.

First, we were trimming space from the line once to decide whether the
line was empty, and then trimming space again if we determined it
wasn't empty.  This only needs to be done once.

Then, do all the trimming (both of whitespace and the prefix) first,
before deciding what to do about the line.

Request BodyAppendix separately when parsing a mail, but not a commit
message.

Add some tests to verify that it works as expected.

Signed-off-by: George Dunlap <george.dunlap@citrix.com>
Co-authored-by: George Dunlap <george.dunlap@citrix.com>

gitdiff/patch_header_test.go

@@ -139,6 +139,7 @@ func TestParsePatchHeader(t *testing.T) {
 	expectedDate := time.Date(2020, 04, 11, 15, 21, 23, 0, time.FixedZone("PDT", -7*60*60))
 	expectedTitle := "A sample commit to test header parsing"
 	expectedBody := "The medium format shows the body, which\nmay wrap on to multiple lines.\n\nAnother body line."
+	expectedBodyAppendix := "CC: Joe Smith <joe.smith@company.com>"
 
 	tests := map[string]struct {
 		Input  string
@@ -221,6 +222,32 @@ CommitDate: Sat Apr 11 15:21:23 2020 -0700
 				Body:          expectedBody,
 			},
 		},
+		"prettyAppendix": {
+			Input: `commit 61f5cd90bed4d204ee3feb3aa41ee91d4734855b
+Author:     Morton Haypenny <mhaypenny@example.com>
+AuthorDate: Sat Apr 11 15:21:23 2020 -0700
+Commit:     Morton Haypenny <mhaypenny@example.com>
+CommitDate: Sat Apr 11 15:21:23 2020 -0700
+
+    A sample commit to test header parsing
+
+    The medium format shows the body, which
+    may wrap on to multiple lines.
+
+    Another body line.
+    ---
+    CC: Joe Smith <joe.smith@company.com>
+`,
+			Header: PatchHeader{
+				SHA:           expectedSHA,
+				Author:        expectedIdentity,
+				AuthorDate:    expectedDate,
+				Committer:     expectedIdentity,
+				CommitterDate: expectedDate,
+				Title:         expectedTitle,
+				Body:          expectedBody + "\n---\n" + expectedBodyAppendix,
+			},
+		},
 		"mailbox": {
 			Input: `From 61f5cd90bed4d204ee3feb3aa41ee91d4734855b Mon Sep 17 00:00:00 2001
 From: Morton Haypenny <mhaypenny@example.com>
@@ -240,6 +267,28 @@ Another body line.
 				Body:       expectedBody,
 			},
 		},
+		"mailboxAppendix": {
+			Input: `From 61f5cd90bed4d204ee3feb3aa41ee91d4734855b Mon Sep 17 00:00:00 2001
+From: Morton Haypenny <mhaypenny@example.com>
+Date: Sat, 11 Apr 2020 15:21:23 -0700
+Subject: [PATCH] A sample commit to test header parsing
+
+The medium format shows the body, which
+may wrap on to multiple lines.
+
+Another body line.
+---
+CC: Joe Smith <joe.smith@company.com>
+`,
+			Header: PatchHeader{
+				SHA:          expectedSHA,
+				Author:       expectedIdentity,
+				AuthorDate:   expectedDate,
+				Title:        expectedTitle,
+				Body:         expectedBody,
+				BodyAppendix: expectedBodyAppendix,
+			},
+		},
 		"unwrapTitle": {
 			Input: `commit 61f5cd90bed4d204ee3feb3aa41ee91d4734855b
 Author: Morton Haypenny <mhaypenny@example.com>
@@ -333,6 +382,10 @@ Author: Morton Haypenny <mhaypenny@example.com>
 			if exp.Body != act.Body {
 				t.Errorf("incorrect parsed body:\n  expected: %q\n    actual: %q", exp.Body, act.Body)
 			}
+			if exp.BodyAppendix != act.BodyAppendix {
+				t.Errorf("incorrect parsed body appendix:\n  expected: %q\n    actual: %q",
+					exp.BodyAppendix, act.BodyAppendix)
+			}
 		})
 	}
 }