Disable colored output on a dumb terminal (#3552)

Enable colored output by default only when the TERM environment variable
is set to a value other than dumb, as git and grep do, so that users no
longer need to pass -M or set NO_COLOR on terminals that cannot display
escape sequences. Colored output is now disabled not only for TERM=dumb
but also when TERM is unset or empty. The -C option still enables colors
in all these cases. On Windows, colored output is still decided by
ANSICON and the console mode, and TERM is not checked.

docs/content/manual/dev/manual.yml

@@ -169,8 +169,10 @@ sections:
         By default, jq outputs colored JSON if writing to a
         terminal. You can force it to produce color even if writing to
         a pipe or a file using `-C`, and disable color with `-M`.
-        When the `NO_COLOR` environment variable is not empty, jq disables
-        colored output by default, but you can enable it by `-C`.
+        When the `NO_COLOR` environment variable is not empty,
+        or the `TERM` environment variable is unset, empty, or set to
+        `dumb`, jq disables colored output by default, but you can
+        enable it by `-C`.
 
         Colors can be configured with the `JQ_COLORS` environment
         variable (see below).

jq.1.prebuilt

@@ -115,7 +115,7 @@ Output the fields of each object with the keys in sorted order\.
 \fB\-\-color\-output\fR / \fB\-C\fR and \fB\-\-monochrome\-output\fR / \fB\-M\fR:
 .
 .IP
-By default, jq outputs colored JSON if writing to a terminal\. You can force it to produce color even if writing to a pipe or a file using \fB\-C\fR, and disable color with \fB\-M\fR\. When the \fBNO_COLOR\fR environment variable is not empty, jq disables colored output by default, but you can enable it by \fB\-C\fR\.
+By default, jq outputs colored JSON if writing to a terminal\. You can force it to produce color even if writing to a pipe or a file using \fB\-C\fR, and disable color with \fB\-M\fR\. When the \fBNO_COLOR\fR environment variable is not empty, or the \fBTERM\fR environment variable is unset, empty, or set to \fBdumb\fR, jq disables colored output by default, but you can enable it by \fB\-C\fR\.
 .
 .IP
 Colors can be configured with the \fBJQ_COLORS\fR environment variable (see below)\.

src/main.c

@@ -543,7 +543,10 @@ int main(int argc, char* argv[]) {
 #ifdef USE_ISATTY
   if (isatty(STDOUT_FILENO)) {
 #ifndef WIN32
-    dumpopts |= JV_PRINT_ISATTY | JV_PRINT_COLOR;
+    dumpopts |= JV_PRINT_ISATTY;
+    char *term = getenv("TERM");
+    if (term != NULL && term[0] != '\0' && strcmp(term, "dumb"))
+      dumpopts |= JV_PRINT_COLOR;
 #else
   /* Verify we actually have the console, as the NUL device is also regarded as
      tty.  Windows can handle color if ANSICON (or ConEmu) is installed, or

tests/shtest

@@ -691,7 +691,7 @@ for colors in '/' '[30' '30m' '30:31m:32' '30:*:31' 'invalid'; do
 done
 unset JQ_COLORS
 
-# Check $NO_COLOR
+# Check $NO_COLOR and $TERM
 test_no_color=true
 $msys  && test_no_color=false
 $mingw && test_no_color=false
@@ -708,22 +708,52 @@ if $test_no_color && command -v script >/dev/null 2>&1; then
       sed 's/^\x5E\x44\x08\x08//'; }
   fi
 
-  faketty $JQ_NO_B -n . > $d/color
+  faketty env TERM=xterm-256color $JQ_NO_B -n . > $d/color
   printf '\033[0;90mnull\033[0m\r\n' > $d/expect
   od -tc $d/expect
   od -tc $d/color
   cmp $d/color $d/expect
-  faketty env NO_COLOR= $JQ_NO_B -n . > $d/color
+  faketty env TERM=xterm-256color NO_COLOR= $JQ_NO_B -n . > $d/color
   printf '\033[0;90mnull\033[0m\r\n' > $d/expect
   od -tc $d/expect
   od -tc $d/color
   cmp $d/color $d/expect
-  faketty env NO_COLOR=1 $JQ_NO_B -n . > $d/color
+  faketty env TERM=xterm-256color NO_COLOR=1 $JQ_NO_B -n . > $d/color
   printf 'null\r\n' > $d/expect
   od -tc $d/expect
   od -tc $d/color
   cmp $d/color $d/expect
-  faketty env NO_COLOR=1 $JQ_NO_B -Cn . > $d/color
+  faketty env TERM=xterm-256color NO_COLOR=1 $JQ_NO_B -Cn . > $d/color
+  printf '\033[0;90mnull\033[0m\r\n' > $d/expect
+  od -tc $d/expect
+  od -tc $d/color
+  cmp $d/color $d/expect
+  faketty env TERM=dumb $JQ_NO_B -n . > $d/color
+  printf 'null\r\n' > $d/expect
+  od -tc $d/expect
+  od -tc $d/color
+  cmp $d/color $d/expect
+  faketty env TERM=dumb $JQ_NO_B -Cn . > $d/color
+  printf '\033[0;90mnull\033[0m\r\n' > $d/expect
+  od -tc $d/expect
+  od -tc $d/color
+  cmp $d/color $d/expect
+  faketty env TERM= $JQ_NO_B -n . > $d/color
+  printf 'null\r\n' > $d/expect
+  od -tc $d/expect
+  od -tc $d/color
+  cmp $d/color $d/expect
+  faketty env TERM= $JQ_NO_B -Cn . > $d/color
+  printf '\033[0;90mnull\033[0m\r\n' > $d/expect
+  od -tc $d/expect
+  od -tc $d/color
+  cmp $d/color $d/expect
+  (unset TERM; faketty $JQ_NO_B -n . > $d/color)
+  printf 'null\r\n' > $d/expect
+  od -tc $d/expect
+  od -tc $d/color
+  cmp $d/color $d/expect
+  (unset TERM; faketty $JQ_NO_B -Cn . > $d/color)
   printf '\033[0;90mnull\033[0m\r\n' > $d/expect
   od -tc $d/expect
   od -tc $d/color