listener: print prompts in plain mode if stdin is tty.

* linenoise/linenoise.c (linenoise): Force the printing of prompts
if the input file descriptor is a tty.

* txr.1: Documentation updated.

2 files changed, 9 insertions, 11 deletions

diff --git a/linenoise/linenoise.c b/linenoise/linenoise.c
index 266542c1..256553d4 100644
--- a/linenoise/linenoise.c
+++ b/linenoise/linenoise.c
@@ -2533,12 +2533,13 @@ wchar_t *linenoise(lino_t *ls, const wchar_t *prompt)
     int count;
     int ifd = lino_os.fileno_fn(ls->tty_ifs);
 
-    if ( ls->noninteractive || !isatty(ifd)) {
+    if (ls->noninteractive || !isatty(ifd)) {
         wchar_t *ret = 0;
         size_t len = 0, i;
         const wchar_t *condensed_prompt = prompt + wcslen(prompt);
+        int show_prompt = ls->show_prompt || (ls->noninteractive && isatty(ifd));
 
-        if (ls->show_prompt) {
+        if (show_prompt) {
             while (condensed_prompt > prompt &&
                    (*condensed_prompt == 0 || *condensed_prompt == ' '))
             {
@@ -2549,7 +2550,7 @@ wchar_t *linenoise(lino_t *ls, const wchar_t *prompt)
         for (;;) {
             size_t nlen;
 
-            if (ls->show_prompt)
+            if (show_prompt)
                 lino_os.puts_fn(ls->tty_ofs, ret ? condensed_prompt : prompt);
 
             /* Not a tty: read from file / pipe. */
diff --git a/txr.1 b/txr.1
index ab260a57..280aff16 100644
--- a/txr.1
+++ b/txr.1
@@ -82533,16 +82533,12 @@ incrementing the prompt number. The
 command prints just the current prompt number, followed by a newline,
 without incrementing the number.
 
-The
+In plain mode, the
 .code :prompt-on
 command enables the printing of prompts. The full prompt is printed before
 reading each new expression. An abbreviated prompt is printed before reading
-the continuation lines of an incomplete expression.
-
-These commands are useful in plain mode, in which no prompts are
-printed by default. See Plain Mode below. The
-.code :prompt-on
-command only has an effect in plain mode.
+the continuation lines of an incomplete expression. The printing of prompts
+is automatically enabled if the input device is an interactive terminal.
 
 None of these prompt-related commands are entered into the history.
 
@@ -82558,7 +82554,8 @@ the listener operates in
 It reads input without providing any editing features: no completion,
 history recall, selection, or copy and paste.  Only the line editing
 features provided by the operating system are available.
-No prompts appear; however, there is still an incrementing counter,
+Prompts appear if standard input is an interactive terminal, or
+if explicitly enabled. There is still an incrementing counter,
 and the numbered variables
 .codn *1 ,
 .codn *2 ,