bug#30320: 26.0.91; Crash when using lsp-ui-doc-mode

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 06 Feb 2018 10:29:04 +0100
> From: martin rudalics <rudalics@gmx.at>
> CC: 30320@debbugs.gnu.org
> 
>  > As for preventing such crashes even though some Lisp does nonsensical
>  > things: I think a TTY frame cannot be less than 3 or 4 lines plus the
>  > number of lines used for the menu bar.  Martin, WDYT about adding
>  > these limitations to adjust_frame_size?
> 
> A better location is when adjusting min_size in frame_windows_min_size
> here:
> 
>        int min_size = XINT (par_size);
> 
>        /* Don't allow phantom frames.  */
>        if (min_size < 1)
> 	min_size = 1;
> 
> As you see we currently allow 1 here for width and height measured in
> characters.  Feel free to change this any way you want -
> FRAME_TERMCAP_P conditioned it shouldn't hurt and be suitable for the
> release version.  If you want me to do it, please tell me the value(s)
> you consider appropriate and where to apply it.
> 
> I never cared about this because I never was able to crash Emacs when
> using small sizes.

Does the below look reasonable and safe for emacs-26?

Jake, can you see if this patch avoids the crash even with the
original problem in lsp-ui-doc-mode?

diff --git a/src/frame.c b/src/frame.c
index d5b080d..b2bc031 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -349,6 +349,7 @@ frame_windows_min_size (Lisp_Object frame, Lisp_Object horizontal,
 {
   struct frame *f = XFRAME (frame);
   Lisp_Object par_size;
+  int retval;
 
   if ((!NILP (horizontal)
        && NUMBERP (par_size = get_frame_param (f, Qmin_width)))
@@ -361,15 +362,27 @@ frame_windows_min_size (Lisp_Object frame, Lisp_Object horizontal,
       if (min_size < 1)
 	min_size = 1;
 
-      return (NILP (pixelwise)
-	      ? min_size
-	      : min_size * (NILP (horizontal)
-			    ? FRAME_LINE_HEIGHT (f)
-			    : FRAME_COLUMN_WIDTH (f)));
+      retval = (NILP (pixelwise)
+		? min_size
+		: min_size * (NILP (horizontal)
+			      ? FRAME_LINE_HEIGHT (f)
+			      : FRAME_COLUMN_WIDTH (f)));
     }
   else
-    return XINT (call4 (Qframe_windows_min_size, frame, horizontal,
-		      ignore, pixelwise));
+    retval = XINT (call4 (Qframe_windows_min_size, frame, horizontal,
+			  ignore, pixelwise));
+  /* Don't allow too snall height of text-mode frames, or else cm.c
+     might abort in cmcheckmagic.  */
+  if ((FRAME_TERMCAP_P (f) || FRAME_MSDOS_P (f)) && NILP (horizontal))
+    {
+      int min_height = (FRAME_MENU_BAR_LINES (f)
+			+ FRAME_WANTS_MODELINE_P (f)
+			+ 2);	/* one text line and one echo-area line */
+      if (retval < min_height)
+	retval = min_height;
+    }
+
+  return retval;
 }