Make src headers idempotent and standalone

Redo src/*.h so that each include file is idempotent (that is, can
be included multiple times with the latter inclusions having no
effect) and standalone (that is, can be included by itself,
with no include file other than config.h needed as a prerequisite).
This is standard practice in GNU programs nowadays.
* lwlib/lwlib-widget.h, src/buffer.h, src/category.h, src/character.h:
* src/charset.h, src/coding.h, src/commands.h, src/disptab.h:
* src/fontset.h, src/gnutls.h, src/indent.h, src/keymap.h, src/macros.h:
* src/regex.h [emacs]:
* src/syntax.h, src/systty.h, src/termhooks.h:
Include lisp.h, for Lisp_Object.
* src/buffer.h, src/category.h, src/cm.h, src/commands.h, src/disptab.h:
* src/indent.h, src/intervals.h, src/keyboard.h, src/macros.h:
* src/process.h, src/puresize.h, src/region-cache.h, src/syntax.h:
* src/syssignal.h, src/sysstdio.h, src/systty.h, src/termchar.h:
* src/termopts.h, src/tparam.h, src/unexec.h:
Protect against multiple inclusion.
* src/buffer.h: Include character.h, for STRING_CHAR.
* src/emacsgtkfixed.h (struct frame):
* src/fontset.h (struct face):
* src/region-cache.h (struct buffer):
* src/termhooks.h (struct glyph):
* src/xsettings.h (struct x_display_info):
Add possibly-forward decl.
* src/syntax.h: Include buffer.h, for BVAR.
* src/sysselect.h: Include lisp.h, for eassume.
* src/termchar.h: Include <stdio.h>, for FILE.
* src/widget.h: Include <X11/IntrinsicP.h>, for Widget.
* src/xsettings.h: Include <X11/Xlib.h>, for XEvent.

32 files changed, 140 insertions, 0 deletions

diff --git a/src/buffer.h b/src/buffer.h
index a0410d454cd..f80530a0cdb 100644
--- a/src/buffer.h
+++ b/src/buffer.h
@@ -18,9 +18,15 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_BUFFER_H
+#define EMACS_BUFFER_H
+
 #include <sys/types.h>
 #include <time.h>
 
+#include "character.h"
+#include "lisp.h"
+
 INLINE_HEADER_BEGIN
 
 /* Accessing the parameters of the current buffer.  */
@@ -1377,3 +1383,5 @@ lowercasep (int c)
 INLINE int upcase (int c) { return uppercasep (c) ? c : upcase1 (c); }
 
 INLINE_HEADER_END
+
+#endif /* EMACS_BUFFER_H */
diff --git a/src/category.h b/src/category.h
index ef784c8cbf5..02f9a193ae8 100644
--- a/src/category.h
+++ b/src/category.h
@@ -22,6 +22,8 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_CATEGORY_H
+#define EMACS_CATEGORY_H
 
 /* We introduce here three types of object: category, category set,
    and category table.
@@ -53,6 +55,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    The second extra slot is a version number of the category table.
    But, for the moment, we are not using this slot.  */
 
+#include "lisp.h"
+
 INLINE_HEADER_BEGIN
 
 #define CATEGORYP(x) RANGED_INTEGERP (0x20, x, 0x7E)
@@ -116,3 +120,5 @@ CHAR_HAS_CATEGORY (int ch, int category)
 extern bool word_boundary_p (int, int);
 
 INLINE_HEADER_END
+
+#endif /* EMACS_CATEGORY_H */
diff --git a/src/character.h b/src/character.h
index 67d4bca4a23..871c1c3de95 100644
--- a/src/character.h
+++ b/src/character.h
@@ -24,6 +24,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #define EMACS_CHARACTER_H
 
 #include <verify.h>
+#include "lisp.h"
 
 INLINE_HEADER_BEGIN
 
diff --git a/src/charset.h b/src/charset.h
index f6575985a47..d2daf2b7e29 100644
--- a/src/charset.h
+++ b/src/charset.h
@@ -28,6 +28,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #define EMACS_CHARSET_H
 
 #include <verify.h>
+#include "lisp.h"
 
 INLINE_HEADER_BEGIN
 
diff --git a/src/cm.h b/src/cm.h
index 829abc083f7..1ade6d1782a 100644
--- a/src/cm.h
+++ b/src/cm.h
@@ -16,6 +16,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_CM_H
+#define EMACS_CM_H
+
 /* Holds the minimum and maximum costs for the parameterized capabilities.  */
 struct parmcap
   {
@@ -166,3 +169,5 @@ extern void cmcostinit (struct tty_display_info *);
 extern void cmgoto (struct tty_display_info *, int, int);
 extern void Wcm_clear (struct tty_display_info *);
 extern int Wcm_init (struct tty_display_info *);
+
+#endif /* EMACS_CM_H */
diff --git a/src/coding.h b/src/coding.h
index c73a9cc3263..2bf51c48883 100644
--- a/src/coding.h
+++ b/src/coding.h
@@ -26,6 +26,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef EMACS_CODING_H
 #define EMACS_CODING_H
 
+#include "lisp.h"
+
 /* Index to arguments of Fdefine_coding_system_internal.  */
 
 enum define_coding_system_arg_index
diff --git a/src/commands.h b/src/commands.h
index 19cd2e49890..e9383341cc9 100644
--- a/src/commands.h
+++ b/src/commands.h
@@ -16,6 +16,10 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_COMMANDS_H
+#define EMACS_COMMANDS_H
+
+#include "lisp.h"
 
 #define Ctl(c) ((c)&037)
 
@@ -39,3 +43,5 @@ extern Lisp_Object unread_switch_frame;
 /* Nonzero if input is coming from the keyboard.  */
 
 #define INTERACTIVE (NILP (Vexecuting_kbd_macro) && !noninteractive)
+
+#endif /* EMACS_COMMANDS_H */
diff --git a/src/disptab.h b/src/disptab.h
index 7afc862312a..3a319c4d217 100644
--- a/src/disptab.h
+++ b/src/disptab.h
@@ -18,6 +18,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* Access the slots of a display-table, according to their purpose.  */
 
+#ifndef EMACS_DISPTAB_H
+#define EMACS_DISPTAB_H
+
+#include "lisp.h"
+
 #define DISP_TABLE_P(obj)                                                   \
   (CHAR_TABLE_P (obj)                                                       \
    && EQ (XCHAR_TABLE (obj)->purpose, Qdisplay_table)                       \
@@ -92,3 +97,5 @@ extern struct Lisp_Char_Table *buffer_display_table (void);
 
 #define SET_GLYPH_FROM_CHAR(glyph, c) \
   SET_GLYPH (glyph, c, DEFAULT_FACE_ID)
+
+#endif /* EMACS_DISPTAB_H */
diff --git a/src/emacsgtkfixed.h b/src/emacsgtkfixed.h
index bcf1cd9072e..a969a6d265b 100644
--- a/src/emacsgtkfixed.h
+++ b/src/emacsgtkfixed.h
@@ -23,6 +23,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <gtk/gtk.h>
 
+struct frame;
+
 G_BEGIN_DECLS
 
 extern GtkWidget *emacs_fixed_new (struct frame *f);
diff --git a/src/fontset.h b/src/fontset.h
index 610394431e1..aa69051fc05 100644
--- a/src/fontset.h
+++ b/src/fontset.h
@@ -26,6 +26,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef EMACS_FONTSET_H
 #define EMACS_FONTSET_H
 
+#include "lisp.h"
+
+struct face;
+
 extern void free_face_fontset (struct frame *, struct face *);
 extern int face_for_char (struct frame *, struct face *, int,
                           ptrdiff_t, Lisp_Object);
diff --git a/src/gnutls.h b/src/gnutls.h
index fd696820aec..9c804b8bd59 100644
--- a/src/gnutls.h
+++ b/src/gnutls.h
@@ -23,6 +23,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <gnutls/gnutls.h>
 #include <gnutls/x509.h>
 
+#include "lisp.h"
+
 /* This limits the attempts to handshake per process (connection).  */
 #define GNUTLS_EMACS_HANDSHAKES_LIMIT 100
 
diff --git a/src/indent.h b/src/indent.h
index cece9e4f33b..037fd744521 100644
--- a/src/indent.h
+++ b/src/indent.h
@@ -16,6 +16,11 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_INDENT_H
+#define EMACS_INDENT_H
+
+#include "lisp.h"
+
 struct position
   {
     ptrdiff_t bufpos;
@@ -51,3 +56,5 @@ bool disptab_matches_widthtab (struct Lisp_Char_Table *disptab,
 /* Recompute BUF's width table, using the display table DISPTAB.  */
 void recompute_width_table (struct buffer *buf,
                             struct Lisp_Char_Table *disptab);
+
+#endif /* EMACS_INDENT_H */
diff --git a/src/intervals.h b/src/intervals.h
index 30fb4b10b02..5a7829de93c 100644
--- a/src/intervals.h
+++ b/src/intervals.h
@@ -16,6 +16,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_INTERVALS_H
+#define EMACS_INTERVALS_H
+
 #include "dispextern.h"
 
 INLINE_HEADER_BEGIN
@@ -295,3 +298,5 @@ extern void syms_of_textprop (void);
 #include "composite.h"
 
 INLINE_HEADER_END
+
+#endif /* EMACS_INTERVALS_H */
diff --git a/src/keyboard.h b/src/keyboard.h
index 0402e0a582c..67afc3bc2be 100644
--- a/src/keyboard.h
+++ b/src/keyboard.h
@@ -17,6 +17,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_KEYBOARD_H
+#define EMACS_KEYBOARD_H
+
 #include "systime.h"            /* for struct timespec, Time */
 #include "coding.h"             /* for ENCODE_UTF_8 and ENCODE_SYSTEM */
 #include "termhooks.h"
@@ -483,3 +486,5 @@ extern const char *const lispy_function_keys[];
 #endif
 
 INLINE_HEADER_END
+
+#endif /* EMACS_KEYBOARD_H */
diff --git a/src/keymap.h b/src/keymap.h
index 215dd3f289f..e7a3b0a2436 100644
--- a/src/keymap.h
+++ b/src/keymap.h
@@ -19,6 +19,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef KEYMAP_H
 #define KEYMAP_H
 
+#include "lisp.h"
+
 /* The maximum byte size consumed by push_key_description.
    All callers should assure that at least this size of memory is
    allocated at the place pointed by the second argument.
diff --git a/src/macros.h b/src/macros.h
index eab8041e72d..46150ad73ae 100644
--- a/src/macros.h
+++ b/src/macros.h
@@ -16,6 +16,10 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_MACROS_H
+#define EMACS_MACROS_H
+
+#include "lisp.h"
 
 /* Number of successful iterations so far
    for innermost keyboard macro.
@@ -42,3 +46,5 @@ extern void finalize_kbd_macro_chars (void);
 /* Store a character into kbd macro being defined */
 
 extern void store_kbd_macro_char (Lisp_Object);
+
+#endif /* EMACS_MACROS_H */
diff --git a/src/process.h b/src/process.h
index 24bad45a24b..9ee5a05ebd2 100644
--- a/src/process.h
+++ b/src/process.h
@@ -16,6 +16,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_PROCESS_H
+#define EMACS_PROCESS_H
+
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>
 #endif
@@ -243,3 +246,5 @@ extern Lisp_Object network_interface_info (Lisp_Object);
 extern Lisp_Object remove_slash_colon (Lisp_Object);
 
 INLINE_HEADER_END
+
+#endif /* EMACS_PROCESS_H */
diff --git a/src/puresize.h b/src/puresize.h
index c61b31f2bde..f07562429d5 100644
--- a/src/puresize.h
+++ b/src/puresize.h
@@ -16,6 +16,11 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_PURESIZE_H
+#define EMACS_PURESIZE_H
+
+#include "lisp.h"
+
 INLINE_HEADER_BEGIN
 
 /* Define PURESIZE, the number of bytes of pure Lisp code to leave space for.
@@ -92,3 +97,5 @@ CHECK_IMPURE (Lisp_Object obj, void *ptr)
 }
 
 INLINE_HEADER_END
+
+#endif /* EMACS_PURESIZE_H */
diff --git a/src/regex.h b/src/regex.h
index c89ca46d4bd..eaa7729a5fb 100644
--- a/src/regex.h
+++ b/src/regex.h
@@ -167,6 +167,7 @@ typedef unsigned long reg_syntax_t;
 extern reg_syntax_t re_syntax_options;
 
 #ifdef emacs
+# include "lisp.h"
 /* In Emacs, this is the string or buffer in which we
    are matching.  It is used for looking up syntax properties.  */
 extern Lisp_Object re_match_object;
diff --git a/src/region-cache.h b/src/region-cache.h
index 1f336cebaf7..2814df47c23 100644
--- a/src/region-cache.h
+++ b/src/region-cache.h
@@ -18,6 +18,8 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_REGION_CACHE_H
+#define EMACS_REGION_CACHE_H
 
 /* This code was written by Jim Blandy <jimb@cs.oberlin.edu> to help
    GNU Emacs better support the gene editor written for the University
@@ -60,6 +62,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
    this region has property P" vs. "I don't know if this region has
    property P or not."  */
 
+struct buffer;
 
 /* Allocate, initialize and return a new, empty region cache.  */
 struct region_cache *new_region_cache (void);
@@ -105,3 +108,5 @@ extern int region_cache_forward (struct buffer *buf, struct region_cache *c,
 /* Likewise, except before POS rather than after POS.  */
 extern int region_cache_backward (struct buffer *buf, struct region_cache *c,
                                   ptrdiff_t pos, ptrdiff_t *next);
+
+#endif /* EMACS_REGION_CACHE_H */
diff --git a/src/syntax.h b/src/syntax.h
index 34b652ba9c8..06ce0ec55df 100644
--- a/src/syntax.h
+++ b/src/syntax.h
@@ -18,6 +18,12 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_SYNTAX_H
+#define EMACS_SYNTAX_H
+
+#include "buffer.h"
+#include "lisp.h"
+
 INLINE_HEADER_BEGIN
 
 extern void update_syntax_table (ptrdiff_t, EMACS_INT, bool, Lisp_Object);
@@ -213,3 +219,5 @@ extern ptrdiff_t scan_words (ptrdiff_t, EMACS_INT);
 extern void SETUP_SYNTAX_TABLE_FOR_OBJECT (Lisp_Object, ptrdiff_t, ptrdiff_t);
 
 INLINE_HEADER_END
+
+#endif /* EMACS_SYNTAX_H */
diff --git a/src/sysselect.h b/src/sysselect.h
index 54f90fb3965..d6c5d1c7148 100644
--- a/src/sysselect.h
+++ b/src/sysselect.h
@@ -23,6 +23,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <sys/select.h>
 #endif
 
+#include "lisp.h"
+
 /* The w32 build defines select stuff in w32.h, which is included
    where w32 needs it, but not where sysselect.h is included.  The w32
    definitions in w32.h are incompatible with the below.  */
diff --git a/src/syssignal.h b/src/syssignal.h
index 5c14479ccad..ec6099408c4 100644
--- a/src/syssignal.h
+++ b/src/syssignal.h
@@ -17,6 +17,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_SYSSIGNAL_H
+#define EMACS_SYSSIGNAL_H
+
 #include <signal.h>
 
 extern void init_signals (bool);
@@ -72,3 +75,5 @@ char const *safe_strsignal (int) ATTRIBUTE_CONST;
 #endif
 
 void deliver_process_signal (int, signal_handler_t);
+
+#endif /* EMACS_SYSSIGNAL_H */
diff --git a/src/sysstdio.h b/src/sysstdio.h
index c97c4f883fc..166823049d2 100644
--- a/src/sysstdio.h
+++ b/src/sysstdio.h
@@ -17,6 +17,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_SYSSTDIO_H
+#define EMACS_SYSSTDIO_H
+
 #include <fcntl.h>
 #include <stdio.h>
 
@@ -29,3 +32,5 @@ extern FILE *emacs_fopen (char const *, char const *);
 # define FOPEN_BINARY ""
 # define FOPEN_TEXT ""
 #endif
+
+#endif /* EMACS_SYSSTDIO_H */
diff --git a/src/systty.h b/src/systty.h
index 3a461565e5d..1022455c588 100644
--- a/src/systty.h
+++ b/src/systty.h
@@ -16,6 +16,9 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_SYSTTY_H
+#define EMACS_SYSTTY_H
+
 /* Include the proper files.  */
 
 #ifndef DOS_NT
@@ -37,6 +40,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 #include <unistd.h>
 
+#include "lisp.h"
+
 
 /* Try to establish the correct character to disable terminal functions
    in a system-independent manner.  Note that USG (at least) define
@@ -85,3 +90,5 @@ extern int emacs_set_tty (int, struct emacs_tty *, bool) EXTERNALLY_VISIBLE;
 extern void suppress_echo_on_tty (int);
 extern int serial_open (Lisp_Object);
 extern void serial_configure (struct Lisp_Process *, Lisp_Object);
+
+#endif /* EMACS_SYSTTY_H */
diff --git a/src/termchar.h b/src/termchar.h
index d8066d7b2b3..06c042797b6 100644
--- a/src/termchar.h
+++ b/src/termchar.h
@@ -16,6 +16,10 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_TERMCHAR_H
+#define EMACS_TERMCHAR_H
+
+#include <stdio.h>
 #include "dispextern.h"
 
 /* Each termcap frame points to its own struct tty_output object in
@@ -230,3 +234,5 @@ extern struct tty_display_info *tty_list;
    : (emacs_abort (), (struct tty_display_info *) 0))
 
 #define CURTTY() FRAME_TTY (SELECTED_FRAME())
+
+#endif /* EMACS_TERMCHAR_H */
diff --git a/src/termhooks.h b/src/termhooks.h
index 88c62df7205..8bde9877c33 100644
--- a/src/termhooks.h
+++ b/src/termhooks.h
@@ -23,8 +23,11 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
 /* Miscellanea.   */
 
+#include "lisp.h"
 #include "systime.h" /* for Time */
 
+struct glyph;
+
 INLINE_HEADER_BEGIN
 
 enum scroll_bar_part {
diff --git a/src/termopts.h b/src/termopts.h
index c54d392ddaf..c5cd56316ce 100644
--- a/src/termopts.h
+++ b/src/termopts.h
@@ -17,9 +17,13 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_TERMOPTS_H
+#define EMACS_TERMOPTS_H
 
 /* Nonzero means use interrupt-driven input.  */
 extern bool interrupt_input;
 
 /* Nonzero while interrupts are temporarily deferred during redisplay.  */
 extern bool interrupts_deferred;
+
+#endif /* EMACS_TERMOPTS_H */
diff --git a/src/tparam.h b/src/tparam.h
index 59fc859c4a3..b391e89094f 100644
--- a/src/tparam.h
+++ b/src/tparam.h
@@ -17,6 +17,8 @@ GNU General Public License for more details.
 You should have received a copy of the GNU General Public License
 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 
+#ifndef EMACS_TPARAM_H
+#define EMACS_TPARAM_H
 
 /* Don't try to include termcap.h.  On some systems, configure finds a
    non-standard termcap.h that the main build won't find.  */
@@ -33,3 +35,5 @@ char *tparam (const char *, char *, int, int, int, int, int);
 extern char PC;
 extern char *BC;
 extern char *UP;
+
+#endif /* EMACS_TPARAM_H */
diff --git a/src/unexec.h b/src/unexec.h
index 343eb6d8db5..cdb2e8016ea 100644
--- a/src/unexec.h
+++ b/src/unexec.h
@@ -1 +1,4 @@
+#ifndef EMACS_UNEXEC_H
+#define EMACS_UNEXEC_H
 void unexec (const char *, const char *);
+#endif /* EMACS_UNEXEC_H */
diff --git a/src/widget.h b/src/widget.h
index a782035d72d..e2e19b0d40f 100644
--- a/src/widget.h
+++ b/src/widget.h
@@ -21,6 +21,8 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef _EmacsFrame_h
 #define _EmacsFrame_h
 
+#include <X11/IntrinsicP.h>
+
 #define XtNminibuffer "minibuffer"
 #define XtCMinibuffer "Minibuffer"
 #define XtNunsplittable "unsplittable"
diff --git a/src/xsettings.h b/src/xsettings.h
index 7ef94a03a89..71b71d6e922 100644
--- a/src/xsettings.h
+++ b/src/xsettings.h
@@ -20,6 +20,10 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #ifndef XSETTINGS_H
 #define XSETTINGS_H
 
+#include <X11/Xlib.h>
+
+struct x_display_info;
+
 extern void xsettings_initialize (struct x_display_info *);
 extern void xft_settings_event (struct x_display_info *, const XEvent *);
 extern const char *xsettings_get_system_font (void);