From 9f8d62ab644553b11286dbcd283db56c83d6ebdd Mon Sep 17 00:00:00 2001
From: Ori Bernstein <ori@eigenstate.org>
Date: Tue, 22 Sep 2020 19:24:01 -0700
Subject: [PATCH] libc: ignore '?' in date format strings

Ignoring '?' when formatting date strings allows
the format strings to be reused for parsing. This
is convenient, since we don't need to duplicate
the format strings.
---
 sys/man/2/tmdate         | 7 ++++---
 sys/src/libc/port/date.c | 3 +++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/sys/man/2/tmdate b/sys/man/2/tmdate
index e4123c3e1..ba5c4441a 100644
--- a/sys/man/2/tmdate
+++ b/sys/man/2/tmdate
@@ -134,8 +134,7 @@ For example,
 will format to a width of 3. When parsing, this acts as whitespace.
 .TP
 .B ?
-When parsing, this makes the following argument match fuzzily.
-Fuzzy matching means that all formats are tried, from most to least specific.
+When parsing, all formats of the following argument are tried from most to least specific.
 For example, 
 .I ?M
 will match 
@@ -144,7 +143,9 @@ will match
 .IR 01 ,
 and 
 .IR 1 ,
-in that order of preference.
+in that order. When formatting,
+.B ?
+is ignored.
 .TP
 .B ~
 When parsing a date, this slackens range enforcement, accepting
diff --git a/sys/src/libc/port/date.c b/sys/src/libc/port/date.c
index 1c90a7985..7be6cb52f 100644
--- a/sys/src/libc/port/date.c
+++ b/sys/src/libc/port/date.c
@@ -428,6 +428,9 @@ static int
 		switch(c0){
 		case 0:
 			break;
+		/* Ignore '?' so we can share parse and format strings */
+		case '?':
+			continue;
 		case 'Y':
 			switch(w){
 			case 1:	n += fmtprint(f, "%*d", pad, tm->year + 1900);		break;