mailinfo: always clean up rfc822 header folding

Without the "-k" option, mailinfo will convert a folded
subject header like:

  Subject: this is a
    subject that doesn't
    fit on one line

into a single line. With "-k", however, we assumed that
these newlines were significant and represented something
that the sending side would want us to preserve.

For messages created by format-patch, this assumption was
broken by a1f6baa (format-patch: wrap long header lines,
2011-02-23).  For messages sent by arbitrary MUAs, this was
probably never a good assumption to make, as they may have
been folding subjects in accordance with rfc822's line
length recommendations all along.

This patch now joins folded lines with a single whitespace
character. This treats header folding purely as a syntactic
feature of the transport mechanism, not as something that
format-patch is trying to tell us about the original
subject.

Signed-off-by: Jeff King <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: peff

builtin/mailinfo.c

@@ -400,7 +400,7 @@ static int read_one_header_line(struct strbuf *line, FILE *in)
 			break;
 		if (strbuf_getline(&continuation, in, '\n'))
 			break;
-		continuation.buf[0] = '\n';
+		continuation.buf[0] = ' ';
 		strbuf_rtrim(&continuation);
 		strbuf_addbuf(line, &continuation);
 	}

t/t4152-am-subjects.sh

@@ -58,7 +58,7 @@ test_expect_success 'long subject preserved (format-patch | am)' '
 test_expect_success 'long subject preserved (format-patch -k | am)' '
 	check_subject long-k
 '
-test_expect_failure 'long subject preserved (format-patch -k | am -k)' '
+test_expect_success 'long subject preserved (format-patch -k | am -k)' '
 	check_subject long-k -k
 '