Fix automatic DPI adjustment and add workarounds for some systems

* lisp/faces.el (x-create-frame-with-faces): New field
`delayed-font'.  Set the `font-parameter' property to `font' in
the given parameter list after face-set-after-frame-default is
called.
* src/fontset.c (Fset_fontset_font): Avoid changing
`font-parameter' with the call to Fmodify_frame_parameters.
* src/frame.c (gui_set_frame_parameters_1): New function.
Factor out gui_set_frame_parameters here, and add an argument
DEFAULT_PARAMETER.  If the `font' parameter is set, and
`default_parameter' is not, then set the `font-parameter' frame
parameter to the `font' parameter as well, to keep track of
which user-specified `font' frame parameter set the default
face's font on the frame.
(gui_set_frame_parameters): Call gui_set_frame_parameters_1 with
new arg set to false.
(gui_set_font): Remove broken implementation of
`font-parameter'.
(gui_default_parameter): If the default value was used, then
call gui_set_frame_parameters_1 with the new argument set to
false.  This is because no font was specified as a frame
parameter by the user, so Freconsider_frame_fonts is free to do
anything it wants.
(Freconsider_frame_fonts): If `font-parameter' is set, then use
it.
(syms_of_frame): New defsym Qfont_parameter.

* src/frame.h: Update prototypes.

* src/haikuterm.c (haiku_default_font_parameter):
* src/pgtkfns.c (pgtk_default_font_parameter):
* src/w32fns.c (w32_default_font_parameter): Stop setting
`font-parameter' here.  This code resulted in decades of
automatic font rescaling not working correctly.

* src/xfaces.c (set_font_frame_param): Clear the
`font-parameter' frame parameter.
(Finternal_merge_in_global_face):
* src/xfns.c (x_default_font_parameter): Avoid changing
`font-parameter' in response to changes to face attributes.
* src/xsettings.c (apply_xft_settings): Add workaround for
Cairo.  (bug#59371, bug#59347, bug#59283, bug#59271, bug#59285,
bug#59306.)

9 files changed, 102 insertions, 56 deletions

diff --git a/src/fontset.c b/src/fontset.c
index 4b91eff2ef6..b82737d005a 100644
--- a/src/fontset.c
+++ b/src/fontset.c
@@ -1663,7 +1663,17 @@ overwrites the previous settings.  */)
             {
               update_auto_fontset_alist (font_object, fontset_obj);
               AUTO_FRAME_ARG (arg, Qfont, Fcons (fontset, font_object));
-              Fmodify_frame_parameters (fr, arg);
+
+#ifdef HAVE_WINDOW_SYSTEM
+              if (FRAME_WINDOW_P (f))
+                /* This is a window-system frame.  Prevent changes of
+                   the `font' parameter here from messing with the
+                   `font-parameter' frame property, as the frame
+                   parameter is not being changed by the user.  */
+                gui_set_frame_parameters_1 (f, arg, true);
+              else
+#endif
+                Fmodify_frame_parameters (fr, arg);
             }
         }
     }
diff --git a/src/frame.c b/src/frame.c
index 151a4029958..b57b296be54 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -4119,10 +4119,17 @@ frame_float (struct frame *f, Lisp_Object val, enum frame_float_type what,
    If a parameter is not specially recognized, do nothing special;
    otherwise call the `gui_set_...' function for that parameter.
    Except for certain geometry properties, always call store_frame_param
-   to store the new value in the parameter alist.  */
+   to store the new value in the parameter alist.
+
+   DEFAULT_PARAMETER should be set if the alist was not specified by
+   the user, or by the face code to set the `font' parameter.  In that
+   case, the `font-parameter' frame parameter should not be changed,
+   so dynamic-setting.el can restore the user's selected font
+   correctly.  */
 
 void
-gui_set_frame_parameters (struct frame *f, Lisp_Object alist)
+gui_set_frame_parameters_1 (struct frame *f, Lisp_Object alist,
+                            bool default_parameter)
 {
   Lisp_Object tail, frame;
 
@@ -4249,7 +4256,7 @@ gui_set_frame_parameters (struct frame *f, Lisp_Object alist)
         }
       else
         {
-          register Lisp_Object param_index, old_value;
+          Lisp_Object param_index, old_value;
 
           old_value = get_frame_param (f, prop);
 
@@ -4260,6 +4267,12 @@ gui_set_frame_parameters (struct frame *f, Lisp_Object alist)
               && XFIXNAT (param_index) < ARRAYELTS (frame_parms)
               && FRAME_RIF (f)->frame_parm_handlers[XFIXNUM (param_index)])
             (*(FRAME_RIF (f)->frame_parm_handlers[XFIXNUM (param_index)])) (f, val, old_value);
+
+          if (!default_parameter && EQ (prop, Qfont))
+            /* The user manually specified the `font' frame parameter.
+               Save that parameter for future use by the
+               dynamic-setting code.  */
+            store_frame_param (f, Qfont_parameter, val);
         }
     }
 
@@ -4410,6 +4423,11 @@ gui_set_frame_parameters (struct frame *f, Lisp_Object alist)
   SAFE_FREE ();
 }
 
+void
+gui_set_frame_parameters (struct frame *f, Lisp_Object alist)
+{
+  gui_set_frame_parameters_1 (f, alist, false);
+}
 
 /* Insert a description of internally-recorded parameters of frame F
    into the parameter alist *ALISTPTR that is to be given to the user.
@@ -4586,9 +4604,6 @@ gui_set_font (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
 {
   Lisp_Object font_object;
   int fontset = -1;
-#ifdef HAVE_X_WINDOWS
-  Lisp_Object font_param = arg;
-#endif
 
   /* Set the frame parameter back to the old value because we may
      fail to use ARG as the new parameter value.  */
@@ -4627,16 +4642,10 @@ gui_set_font (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
         error ("Unknown fontset: %s", SDATA (XCAR (arg)));
       font_object = XCDR (arg);
       arg = AREF (font_object, FONT_NAME_INDEX);
-#ifdef HAVE_X_WINDOWS
-      font_param = Ffont_get (font_object, QCname);
-#endif
     }
   else if (FONT_OBJECT_P (arg))
     {
       font_object = arg;
-#ifdef HAVE_X_WINDOWS
-      font_param = Ffont_get (font_object, QCname);
-#endif
       /* This is to store the XLFD font name in the frame parameter for
          backward compatibility.  We should store the font-object
          itself in the future.  */
@@ -4667,9 +4676,7 @@ gui_set_font (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
   if (FRAME_TERMINAL (f)->set_new_font_hook)
     FRAME_TERMINAL (f)->set_new_font_hook (f, font_object, fontset);
   store_frame_param (f, Qfont, arg);
-#ifdef HAVE_X_WINDOWS
-  store_frame_param (f, Qfont_parameter, font_param);
-#endif
+
   /* Recalculate tabbar height.  */
   f->n_tab_bar_rows = 0;
   /* Recalculate toolbar height.  */
@@ -5451,12 +5458,20 @@ gui_default_parameter (struct frame *f, Lisp_Object alist, Lisp_Object prop,
                        enum resource_types type)
 {
   Lisp_Object tem;
+  bool was_unbound;
 
   tem = gui_frame_get_arg (f, alist, prop, xprop, xclass, type);
+
   if (BASE_EQ (tem, Qunbound))
-    tem = deflt;
+    {
+      tem = deflt;
+      was_unbound = true;
+    }
+  else
+    was_unbound = false;
+
   AUTO_FRAME_ARG (arg, prop, tem);
-  gui_set_frame_parameters (f, arg);
+  gui_set_frame_parameters_1 (f, arg, was_unbound);
   return tem;
 }
 
@@ -5959,16 +5974,26 @@ have changed.  */)
   (Lisp_Object frame)
 {
   struct frame *f;
-  Lisp_Object params;
+  Lisp_Object params, font_parameter;
 
   f = decode_window_system_frame (frame);
 
   /* Kludge: if a `font' parameter was already specified,
-     create an alist containing just that parameter.  (bug#59371) */
+     create an alist containing just that parameter.  (bug#59371)
+
+     This sounds so simple, right?  Well, read on below: */
   params = Qnil;
 
-  if (!NILP (get_frame_param (f, Qfont)))
-    params = list1 (Fcons (Qfont, get_frame_param (f, Qfont)));
+  /* The difference between Qfont and Qfont_parameter is that the
+     latter is not set automatically by the likes of x_new_font, and
+     implicitly as the default face is realized.  It is only set when
+     the user specifically specifies a `font' frame parameter, and is
+     cleared the moment the frame's font becomes defined by a face
+     attribute, instead of through the `font' frame parameter.  */
+  font_parameter = get_frame_param (f, Qfont_parameter);
+
+  if (!NILP (font_parameter))
+    params = list1 (Fcons (Qfont, font_parameter));
 
   /* First, call this to reinitialize any font backend specific
      stuff.  */
@@ -5976,10 +6001,22 @@ have changed.  */)
   if (FRAME_RIF (f)->default_font_parameter)
     FRAME_RIF (f)->default_font_parameter (f, params);
 
+  /* For a mysterious reason, x_default_font_parameter sets Qfont to
+     nil in the alist!  */
+
+  if (!NILP (font_parameter))
+    params = list1 (Fcons (Qfont, font_parameter));
+
   /* Now call this to apply the existing value(s) of the `default'
      face.  */
   call2 (Qface_set_after_frame_default, frame, params);
 
+  /* Restore the value of the `font-parameter' parameter, as
+     `face-set-after-frame-default' will have changed it through its
+     calls to `set-face-attribute'.  */
+  if (!NILP (font_parameter))
+    store_frame_param (f, Qfont_parameter, font_parameter);
+
   return Qnil;
 }
 
@@ -6240,6 +6277,7 @@ syms_of_frame (void)
   DEFSYM (Qiconify_top_level, "iconify-top-level");
   DEFSYM (Qmake_invisible, "make-invisible");
   DEFSYM (Quse_frame_synchronization, "use-frame-synchronization");
+  DEFSYM (Qfont_parameter, "font-parameter");
 
   {
     int i;
diff --git a/src/frame.h b/src/frame.h
index 458b6257e49..d6fd62b2ac2 100644
--- a/src/frame.h
+++ b/src/frame.h
@@ -1670,6 +1670,7 @@ IMAGE_OPT_FROM_ID (struct frame *f, int id)
 /* The class of this X application.  */
 #define EMACS_CLASS "Emacs"
 
+extern void gui_set_frame_parameters_1 (struct frame *, Lisp_Object, bool);
 extern void gui_set_frame_parameters (struct frame *, Lisp_Object);
 extern void gui_set_fullscreen (struct frame *, Lisp_Object, Lisp_Object);
 extern void gui_set_line_spacing (struct frame *, Lisp_Object, Lisp_Object);
diff --git a/src/haikuterm.c b/src/haikuterm.c
index 4e32b747160..496480cbc09 100644
--- a/src/haikuterm.c
+++ b/src/haikuterm.c
@@ -3007,9 +3007,11 @@ haiku_default_font_parameter (struct frame *f, Lisp_Object parms)
     font = font_open_by_spec (f, Ffont_get_system_font ());
 
   if (NILP (font))
-      font = !NILP (font_param) ? font_param
-      : gui_display_get_arg (dpyinfo, parms, Qfont, "font", "Font",
-                             RES_TYPE_STRING);
+    font = (!NILP (font_param)
+            ? font_param
+            : gui_display_get_arg (dpyinfo, parms, Qfont,
+                                   "font", "Font",
+                                   RES_TYPE_STRING));
 
   if (! FONTP (font) && ! STRINGP (font))
     {
@@ -3029,13 +3031,6 @@ haiku_default_font_parameter (struct frame *f, Lisp_Object parms)
       if (NILP (font))
         error ("No suitable font was found");
     }
-  else if (!NILP (font_param))
-    {
-      /* Remember the explicit font parameter, so we can re-apply it
-         after we've applied the `default' face settings.  */
-      AUTO_FRAME_ARG (arg, Qfont_parameter, font_param);
-      gui_set_frame_parameters (f, arg);
-    }
 
   gui_default_parameter (f, parms, Qfont, font, "font", "Font",
                          RES_TYPE_STRING);
diff --git a/src/pgtkfns.c b/src/pgtkfns.c
index f370f039780..a32067af818 100644
--- a/src/pgtkfns.c
+++ b/src/pgtkfns.c
@@ -1121,13 +1121,6 @@ pgtk_default_font_parameter (struct frame *f, Lisp_Object parms)
       if (NILP (font))
         error ("No suitable font was found");
     }
-  else if (!NILP (font_param))
-    {
-      /* Remember the explicit font parameter, so we can re-apply it after
-         we've applied the `default' face settings.  */
-      AUTO_FRAME_ARG (arg, Qfont_parameter, font_param);
-      gui_set_frame_parameters (f, arg);
-    }
 
   /* This call will make X resources override any system font setting.  */
   gui_default_parameter (f, parms, Qfont, font, "font", "Font",
diff --git a/src/w32fns.c b/src/w32fns.c
index e441665804e..887e5a1f7b7 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -5794,13 +5794,7 @@ w32_default_font_parameter (struct frame *f, Lisp_Object parms)
       if (NILP (font))
         error ("No suitable font was found");
     }
-  else if (!NILP (font_param))
-    {
-      /* Remember the explicit font parameter, so we can re-apply it after
-         we've applied the `default' face settings.  */
-      gui_set_frame_parameters (f, Fcons (Fcons (Qfont_parameter, font_param),
-                                          Qnil));
-    }
+
   gui_default_parameter (f, parms, Qfont, font, "font", "Font", RES_TYPE_STRING);
 }
 
diff --git a/src/xfaces.c b/src/xfaces.c
index ed76db9adb7..df078227c8a 100644
--- a/src/xfaces.c
+++ b/src/xfaces.c
@@ -3809,8 +3809,12 @@ set_font_frame_param (Lisp_Object frame, Lisp_Object lface)
           ASET (lface, LFACE_FONT_INDEX, font);
         }
       f->default_face_done_p = false;
-      AUTO_FRAME_ARG (arg, Qfont, font);
-      Fmodify_frame_parameters (frame, arg);
+      AUTO_LIST2 (arg, AUTO_CONS_EXPR (Qfont, font),
+                  /* Clear the `font-parameter' frame property, as the
+                     font is now being specified by a face, not a
+                     frame property.  */
+                  AUTO_CONS_EXPR (Qfont_parameter, Qnil));
+      gui_set_frame_parameters_1 (f, arg, true);
     }
 }
 
@@ -4208,7 +4212,17 @@ Default face attributes override any local face attributes.  */)
             {
               Lisp_Object name = newface->font->props[FONT_NAME_INDEX];
               AUTO_FRAME_ARG (arg, Qfont, name);
-              Fmodify_frame_parameters (frame, arg);
+
+#ifdef HAVE_WINDOW_SYSTEM
+              if (FRAME_WINDOW_P (f))
+                /* This is a window-system frame.  Prevent changes of
+                   the `font' parameter here from messing with the
+                   `font-parameter' frame property, as the frame
+                   parameter is not being changed by the user.  */
+                gui_set_frame_parameters_1 (f, arg, true);
+              else
+#endif
+                Fmodify_frame_parameters (frame, arg);
             }
 
           if (STRINGP (gvec[LFACE_FOREGROUND_INDEX]))
diff --git a/src/xfns.c b/src/xfns.c
index 8ee26d713aa..2ff70f79851 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -4551,13 +4551,6 @@ x_default_font_parameter (struct frame *f, Lisp_Object parms)
       if (NILP (font))
         error ("No suitable font was found");
     }
-  else if (!NILP (font_param))
-    {
-      /* Remember the explicit font parameter, so we can re-apply it after
-         we've applied the `default' face settings.  */
-      AUTO_FRAME_ARG (arg, Qfont_parameter, font_param);
-      gui_set_frame_parameters (f, arg);
-    }
 
   /* This call will make X resources override any system font setting.  */
   gui_default_parameter (f, parms, Qfont, font, "font", "Font", RES_TYPE_STRING);
diff --git a/src/xsettings.c b/src/xsettings.c
index 1a9f1a8d5ae..f1ee84a1a02 100644
--- a/src/xsettings.c
+++ b/src/xsettings.c
@@ -886,6 +886,14 @@ apply_xft_settings (Display_Info *dpyinfo,
     }
 #endif
 
+#ifdef USE_CAIRO
+  /* When Cairo is being used, set oldsettings.dpi to dpyinfo->resx.
+     This is a gross hack, but seeing as Cairo fails to report
+     anything reasonable, just use it to avoid config-changed events
+     being sent at startup.  */
+  oldsettings.dpi = dpyinfo->resx;
+#endif
+
   if ((settings->seen & SEEN_DPI) != 0
       && settings->dpi > 0
       /* The following conjunct avoids setting `changed' to true when