bug#34051: 27.0.50; Emacs 27 from master segfaults

[Alan Third <alan@idiocy.org>]

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On Sun, Jan 13, 2019 at 05:24:33PM +0200, Eli Zaretskii wrote:
> Strange, it looks like it dies in x_parse_color.  Alan, can you
> reproduce this?

These X server errors are asynchronous and not very helpful. The most
likely culprit is x_create_x_image_and_pixmap.

Stefan, please try the attached patch.
-- 
Alan Third

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From 254097a0aadb252f9223e1d133132a01b459bc7d Mon Sep 17 00:00:00 2001
From: Alan Third <alan@idiocy.org>
Date: Tue, 15 Jan 2019 16:38:34 +0000
Subject: [PATCH] Be more specific with XRender bit-depths (bug#34051)

* src/image.c (x_create_x_image_and_pixmap): Fail gracefully if a bit
depth is requested that XRender doesn't support.
---
 src/image.c | 32 +++++++++++++++++++++++---------
 1 file changed, 23 insertions(+), 9 deletions(-)

diff --git a/src/image.c b/src/image.c
index 2fae105815..3f5def2350 100644
--- a/src/image.c
+++ b/src/image.c
@@ -2178,15 +2178,29 @@ x_create_x_image_and_pixmap (struct frame *f, int width, int height, int depth,
   int event_basep, error_basep;
   if (picture && XRenderQueryExtension (display, &event_basep, &error_basep))
     {
-      XRenderPictFormat *format;
-      XRenderPictureAttributes attr;
-
-      /* FIXME: Do we need to handle all possible bit depths?  */
-      format = XRenderFindStandardFormat (display,
-                                          depth > 24 ? PictStandardARGB32
-                                          : depth > 8 ? PictStandardRGB24
-                                          : PictStandardA8);
-      *picture = XRenderCreatePicture (display, *pixmap, format, 0, &attr);
+      if (depth == 32 || depth == 24 || depth == 8)
+        {
+          XRenderPictFormat *format;
+          XRenderPictureAttributes attr;
+
+          /* FIXME: Do we need to handle all possible bit depths?
+             XRenderFindStandardFormat supports PictStandardARGB32,
+             PictStandardRGB24, PictStandardA8, PictStandardA4,
+             PictStandardA1, and PictStandardNUM (what is this?!).
+
+             XRenderFindFormat may support more, but I don't
+             understand the documentation.  */
+          format = XRenderFindStandardFormat (display,
+                                              depth == 32 ? PictStandardARGB32
+                                              : depth == 24 ? PictStandardRGB24
+                                              : PictStandardA8);
+          *picture = XRenderCreatePicture (display, *pixmap, format, 0, &attr);
+        }
+      else
+        {
+          image_error ("Specified bit depth is not supported by XRender");
+          *picture = NULL;
+        }
     }
 # endif
 
-- 
2.19.1