master d0a66f3e0e: Display a warning for some uses of nil in face attributes.

[Gregory Heytings]

branch: master
commit d0a66f3e0e668d8c12c54436740c62f8e238a664
Author: Gregory Heytings <gregory@heytings.org>
Commit: Gregory Heytings <gregory@heytings.org>

    Display a warning for some uses of nil in face attributes.
    
    * src/xfaces.c (HANDLE_INVALID_NIL_VALUE): New macro, which displays
    a warning for invalid uses of nil as a face attribute value.
    (Finternal_set_lisp_face_attribute): Use the macro for the attributes
    :foreground, :distant-foreground and :background.
---
 src/xfaces.c | 21 ++++++++++++---------
 1 file changed, 12 insertions(+), 9 deletions(-)

diff --git a/src/xfaces.c b/src/xfaces.c
index 70d5cbeb4c..5e3a47d7f8 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -3052,6 +3052,15 @@ The value is TO.  */)
 }
 
 
+#define HANDLE_INVALID_NIL_VALUE(A,F)                                  \
+  if (NILP (value))                                                    \
+    {                                                                  \
+      add_to_log ("Warning: setting attribute `%s' of face `%s': nil " \
+                 "value is invalid, use `unspecified' instead.", A, F); \
+      /* Compatibility with 20.x.  */                                  \
+      value = Qunspecified;                                            \
+    }
+
 DEFUN ("internal-set-lisp-face-attribute", Finternal_set_lisp_face_attribute,
        Sinternal_set_lisp_face_attribute, 3, 4, 0,
        doc: /* Set attribute ATTR of FACE to VALUE.
@@ -3390,9 +3399,7 @@ FRAME 0 means change the face on all frames, and change 
the default
     }
   else if (EQ (attr, QCforeground))
     {
-      /* Compatibility with 20.x.  */
-      if (NILP (value))
-       value = Qunspecified;
+      HANDLE_INVALID_NIL_VALUE (QCforeground, face);
       if (!UNSPECIFIEDP (value)
          && !IGNORE_DEFFACE_P (value)
          && !RESET_P (value))
@@ -3409,9 +3416,7 @@ FRAME 0 means change the face on all frames, and change 
the default
     }
   else if (EQ (attr, QCdistant_foreground))
     {
-      /* Compatibility with 20.x.  */
-      if (NILP (value))
-       value = Qunspecified;
+      HANDLE_INVALID_NIL_VALUE (QCdistant_foreground, face);
       if (!UNSPECIFIEDP (value)
          && !IGNORE_DEFFACE_P (value)
          && !RESET_P (value))
@@ -3428,9 +3433,7 @@ FRAME 0 means change the face on all frames, and change 
the default
     }
   else if (EQ (attr, QCbackground))
     {
-      /* Compatibility with 20.x.  */
-      if (NILP (value))
-       value = Qunspecified;
+      HANDLE_INVALID_NIL_VALUE (QCbackground, face);
       if (!UNSPECIFIEDP (value)
          && !IGNORE_DEFFACE_P (value)
          && !RESET_P (value))