Re: [PATCH 1/2] Save terminal width before setting up pager and export term_columns()

[Junio C Hamano <gitster@pobox.com>]

Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl> writes:

> term_columns() checks for terminal width via ioctl(2). After
> redirecting, stdin is no longer terminal to get terminal width.

s/stdin/stdout/

> Check terminal width and save it before redirecting stdin in
> setup_pager() by calling term_columns().
>
> Move term_columns() to pager.c and export it in cache.h.
>
> Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
> ---

Thanks.

It probably is worth mentioning what the end-user visible effect of this
change is somewhere in the log message.

I somehow find "term_columns_cache" a funny name for this variable and
does not describe what it does.  Unlike a real cache, we cannot discard it
and re-read it even if we later wanted to.

I am tempted to rewrite the patch like this to update other minor style
issues.

-- >8 --
From: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Date: Sun, 12 Feb 2012 15:12:32 +0100
Subject: [PATCH] pager: find out the terminal width before spawning the pager

term_columns() checks for terminal width via ioctl(2) on the standard
output, but we spawn the pager too early for this check to be useful.

The effect of this buglet can be observed by opening a wide terminal and
running "git -p help --all", which still shows 80-column output, while
"git help --all" uses the full terminal width. Run the check before we
spawn the pager to fix this.

While at it, move term_columns() to pager.c and export it from cache.h so
that callers other than the help subsystem can use it.

Signed-off-by: Zbigniew Jędrzejewski-Szmek <zbyszek@in.waw.pl>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 cache.h |    1 +
 help.c  |   22 ----------------------
 pager.c |   43 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 44 insertions(+), 22 deletions(-)

diff --git a/cache.h b/cache.h
index 79c612f..c7e3b4d 100644
--- a/cache.h
+++ b/cache.h
@@ -1172,6 +1172,7 @@ extern void setup_pager(void);
 extern const char *pager_program;
 extern int pager_in_use(void);
 extern int pager_use_color;
+extern int term_columns(void);
 
 extern const char *editor_program;
 extern const char *askpass_program;
diff --git a/help.c b/help.c
index cbbe966..14eefc9 100644
--- a/help.c
+++ b/help.c
@@ -5,28 +5,6 @@
 #include "help.h"
 #include "common-cmds.h"
 
-/* most GUI terminals set COLUMNS (although some don't export it) */
-static int term_columns(void)
-{
-	char *col_string = getenv("COLUMNS");
-	int n_cols;
-
-	if (col_string && (n_cols = atoi(col_string)) > 0)
-		return n_cols;
-
-#ifdef TIOCGWINSZ
-	{
-		struct winsize ws;
-		if (!ioctl(1, TIOCGWINSZ, &ws)) {
-			if (ws.ws_col)
-				return ws.ws_col;
-		}
-	}
-#endif
-
-	return 80;
-}
-
 void add_cmdname(struct cmdnames *cmds, const char *name, int len)
 {
 	struct cmdname *ent = xmalloc(sizeof(*ent) + len + 1);
diff --git a/pager.c b/pager.c
index 975955b..e06cfa0 100644
--- a/pager.c
+++ b/pager.c
@@ -76,6 +76,12 @@ void setup_pager(void)
 	if (!pager)
 		return;
 
+	/*
+	 * force computing the width of the terminal before we redirect
+	 * the standard output to the pager.
+	 */
+	(void) term_columns();
+
 	setenv("GIT_PAGER_IN_USE", "true", 1);
 
 	/* spawn the pager */
@@ -110,3 +116,40 @@ int pager_in_use(void)
 	env = getenv("GIT_PAGER_IN_USE");
 	return env ? git_config_bool("GIT_PAGER_IN_USE", env) : 0;
 }
+
+/*
+ * Return cached value (if set) or $COLUMNS (if set and positive) or
+ * ioctl(1, TIOCGWINSZ).ws_col (if positive) or 80.
+ *
+ * $COLUMNS even if set, is usually not exported, so
+ * the variable can be used to override autodection.
+ * This behaviour conforms to The Single UNIX Specification, Version 2
+ * (http://pubs.opengroup.org/onlinepubs/7908799/xbd/envvar.html#tag_002_003).
+ */
+int term_columns(void)
+{
+	static int term_columns_at_startup;
+
+	char *col_string;
+	int n_cols;
+
+	if (term_columns_at_startup)
+		return term_columns_at_startup;
+
+	term_columns_at_startup = 80;
+
+	col_string = getenv("COLUMNS");
+	if (col_string && (n_cols = atoi(col_string)) > 0)
+		term_columns_at_startup = n_cols;
+#ifdef TIOCGWINSZ
+	else {
+		struct winsize ws;
+		if (!ioctl(1, TIOCGWINSZ, &ws)) {
+			if (ws.ws_col) {
+				term_columns_at_startup = ws.ws_col;
+			}
+		}
+	}
+#endif
+	return term_columns_at_startup;
+}
-- 
1.7.9.300.gd47e4