Do not use VISUAL editor on dumb terminals

Refuse to use $VISUAL and fall back to $EDITOR if TERM is unset
or set to "dumb".  Traditionally, VISUAL is set to a screen
editor and EDITOR to a line-based editor, which should be more
useful in that situation.

vim, for example, is happy to assume a terminal supports ANSI
sequences even if TERM is dumb (e.g., when running from a text
editor like Acme).  git already refuses to fall back to vi on a
dumb terminal if GIT_EDITOR, core.editor, VISUAL, and EDITOR are
unset, but without this patch, that check is suppressed by
VISUAL=vi.

Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

editor.c

@@ -4,19 +4,19 @@
 
 int launch_editor(const char *path, struct strbuf *buffer, const char *const *env)
 {
-	const char *editor, *terminal;
+	const char *editor = getenv("GIT_EDITOR");
+	const char *terminal = getenv("TERM");
+	int terminal_is_dumb = !terminal || !strcmp(terminal, "dumb");
 
-	editor = getenv("GIT_EDITOR");
 	if (!editor && editor_program)
 		editor = editor_program;
-	if (!editor)
+	if (!editor && !terminal_is_dumb)
 		editor = getenv("VISUAL");
 	if (!editor)
 		editor = getenv("EDITOR");
 
-	terminal = getenv("TERM");
-	if (!editor && (!terminal || !strcmp(terminal, "dumb")))
-		return error("Terminal is dumb but no VISUAL nor EDITOR defined.");
+	if (!editor && terminal_is_dumb)
+		return error("terminal is dumb, but EDITOR unset");
 
 	if (!editor)
 		editor = "vi";

t/t7005-editor.sh

@@ -42,6 +42,16 @@ test_expect_success 'dumb should error out when falling back on vi' '
 	fi
 '
 
+test_expect_success 'dumb should prefer EDITOR to VISUAL' '
+
+	EDITOR=./e-EDITOR.sh &&
+	VISUAL=./e-VISUAL.sh &&
+	export EDITOR VISUAL &&
+	git commit --amend &&
+	test "$(git show -s --format=%s)" = "Edited by EDITOR"
+
+'
+
 TERM=vt100
 export TERM
 for i in vi EDITOR VISUAL core_editor GIT_EDITOR

t/t7501-commit.sh

@@ -86,7 +86,7 @@ chmod 755 editor
 
 test_expect_success \
 	"amend commit" \
-	"VISUAL=./editor git commit --amend"
+	"EDITOR=./editor git commit --amend"
 
 test_expect_success \
 	"passing -m and -F" \
@@ -107,7 +107,7 @@ chmod 755 editor
 test_expect_success \
 	"editing message from other commit" \
 	"echo 'hula hula' >file && \
-	 VISUAL=./editor git commit -c HEAD^ -a"
+	 EDITOR=./editor git commit -c HEAD^ -a"
 
 test_expect_success \
 	"message from stdin" \
@@ -141,10 +141,10 @@ EOF
 test_expect_success \
 	'editor not invoked if -F is given' '
 	 echo "moo" >file &&
-	 VISUAL=./editor git commit -a -F msg &&
+	 EDITOR=./editor git commit -a -F msg &&
 	 git show -s --pretty=format:"%s" | grep -q good &&
 	 echo "quack" >file &&
-	 echo "Another good message." | VISUAL=./editor git commit -a -F - &&
+	 echo "Another good message." | EDITOR=./editor git commit -a -F - &&
 	 git show -s --pretty=format:"%s" | grep -q good
 	 '
 # We could just check the head sha1, but checking each commit makes it

t/test-lib.sh

@@ -30,7 +30,7 @@ TZ=UTC
 TERM=dumb
 export LANG LC_ALL PAGER TERM TZ
 EDITOR=:
-VISUAL=:
+unset VISUAL
 unset GIT_EDITOR
 unset AUTHOR_DATE
 unset AUTHOR_EMAIL
@@ -58,7 +58,7 @@ GIT_MERGE_VERBOSITY=5
 export GIT_MERGE_VERBOSITY
 export GIT_AUTHOR_EMAIL GIT_AUTHOR_NAME
 export GIT_COMMITTER_EMAIL GIT_COMMITTER_NAME
-export EDITOR VISUAL
+export EDITOR
 GIT_TEST_CMP=${GIT_TEST_CMP:-diff -u}
 
 # Protect ourselves from common misconfiguration to export
@@ -207,8 +207,8 @@ trap 'die' EXIT
 test_set_editor () {
 	FAKE_EDITOR="$1"
 	export FAKE_EDITOR
-	VISUAL='"$FAKE_EDITOR"'
-	export VISUAL
+	EDITOR='"$FAKE_EDITOR"'
+	export EDITOR
 }
 
 test_tick () {