pretty: two phase conversion for non utf-8 commits

Always assume format_commit_item() takes an utf-8 string for string
handling simplicity (we can handle utf-8 strings, but can't with other
encodings).

If commit message is in non-utf8, or output encoding is not, then the
commit is first converted to utf-8, processed, then output converted
to output encoding. This of course only works with encodings that are
compatible with Unicode.

This also fixes the iso8859-1 test in t6006. It's supposed to create
an iso8859-1 commit, but the commit content in t6006 is in UTF-8.
t6006 is now converted back in UTF-8 (the downside is we can't put
utf-8 strings there anymore).

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pretty.c

@@ -954,7 +954,8 @@ static int format_reflog_person(struct strbuf *sb,
 	return format_person_part(sb, part, ident, strlen(ident), dmode);
 }
 
-static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
+static size_t format_commit_one(struct strbuf *sb, /* in UTF-8 */
+				const char *placeholder,
 				void *context)
 {
 	struct format_commit_context *c = context;
@@ -1193,7 +1194,8 @@ static size_t format_commit_one(struct strbuf *sb, const char *placeholder,
 	return 0;	/* unknown placeholder */
 }
 
-static size_t format_commit_item(struct strbuf *sb, const char *placeholder,
+static size_t format_commit_item(struct strbuf *sb, /* in UTF-8 */
+				 const char *placeholder,
 				 void *context)
 {
 	int consumed;
@@ -1273,6 +1275,7 @@ void format_commit_message(const struct commit *commit,
 {
 	struct format_commit_context context;
 	const char *output_enc = pretty_ctx->output_encoding;
+	const char *utf8 = "UTF-8";
 
 	memset(&context, 0, sizeof(context));
 	context.commit = commit;
@@ -1285,6 +1288,23 @@ void format_commit_message(const struct commit *commit,
 	strbuf_expand(sb, format, format_commit_item, &context);
 	rewrap_message_tail(sb, &context, 0, 0, 0);
 
+	if (output_enc) {
+		if (same_encoding(utf8, output_enc))
+			output_enc = NULL;
+	} else {
+		if (context.commit_encoding &&
+		    !same_encoding(context.commit_encoding, utf8))
+			output_enc = context.commit_encoding;
+	}
+
+	if (output_enc) {
+		int outsz;
+		char *out = reencode_string_len(sb->buf, sb->len,
+						output_enc, utf8, &outsz);
+		if (out)
+			strbuf_attach(sb, out, outsz, outsz + 1);
+	}
+
 	free(context.commit_encoding);
 	logmsg_free(context.message, commit);
 	free(context.signature_check.gpg_output);

t/t6006-rev-list-format.sh

@@ -184,7 +184,7 @@ Test printing of complex bodies
 
 This commit message is much longer than the others,
 and it will be encoded in iso8859-1. We should therefore
-include an iso8859 character: ¡bueno!
+include an iso8859 character: ¡bueno!
 EOF
 test_expect_success 'setup complex body' '
 git config i18n.commitencoding iso8859-1 &&
@@ -192,14 +192,14 @@ git config i18n.commitencoding iso8859-1 &&
 '
 
 test_format complex-encoding %e <<'EOF'
-commit f58db70b055c5718631e5c61528b28b12090cdea
+commit 1ed88da4a5b5ed8c449114ac131efc62178734c3
 iso8859-1
 commit 131a310eb913d107dd3c09a65d1651175898735d
 commit 86c75cfd708a0e5868dc876ed5b8bb66c80b4873
 EOF
 
 test_format complex-subject %s <<'EOF'
-commit f58db70b055c5718631e5c61528b28b12090cdea
+commit 1ed88da4a5b5ed8c449114ac131efc62178734c3
 Test printing of complex bodies
 commit 131a310eb913d107dd3c09a65d1651175898735d
 changed foo
@@ -208,17 +208,17 @@ added foo
 EOF
 
 test_format complex-body %b <<'EOF'
-commit f58db70b055c5718631e5c61528b28b12090cdea
+commit 1ed88da4a5b5ed8c449114ac131efc62178734c3
 This commit message is much longer than the others,
 and it will be encoded in iso8859-1. We should therefore
-include an iso8859 character: ¡bueno!
+include an iso8859 character: ¡bueno!
 
 commit 131a310eb913d107dd3c09a65d1651175898735d
 commit 86c75cfd708a0e5868dc876ed5b8bb66c80b4873
 EOF
 
 test_expect_success '%x00 shows NUL' '
-	echo  >expect commit f58db70b055c5718631e5c61528b28b12090cdea &&
+	echo  >expect commit 1ed88da4a5b5ed8c449114ac131efc62178734c3 &&
 	echo >>expect fooQbar &&
 	git rev-list -1 --format=foo%x00bar HEAD >actual.nul &&
 	nul_to_q <actual.nul >actual &&