diff --git a/Makefile b/Makefile
index 5667c9d953..079416eb43 100644
--- a/Makefile
+++ b/Makefile
@@ -151,7 +151,6 @@ iwyu: build/.ran-cmake
 	|src/nvim/buffer_defs.h\
 	|src/nvim/channel.h\
 	|src/nvim/charset.h\
-	|src/nvim/cmdexpand.h\
 	|src/nvim/decoration.h\
 	|src/nvim/drawline.h\
 	|src/nvim/eval.h\
@@ -172,7 +171,6 @@ iwyu: build/.ran-cmake
 	|src/nvim/event/wstream.h\
 	|src/nvim/extmark.h\
 	|src/nvim/garray.h\
-	|src/nvim/getchar.h\
 	|src/nvim/globals.h\
 	|src/nvim/grid.h\
 	|src/nvim/highlight.h\
@@ -187,7 +185,6 @@ iwyu: build/.ran-cmake
 	|src/nvim/msgpack_rpc/helpers.h\
 	|src/nvim/msgpack_rpc/unpacker.h\
 	|src/nvim/option.h\
-	|src/nvim/os/fileio.h\
 	|src/nvim/os/input.h\
 	|src/nvim/os/pty_conpty_win.h\
 	|src/nvim/os/pty_process_unix.h\
diff --git a/src/clint.py b/src/clint.py
index ddd3ff7d44..2a7eb16c9a 100755
--- a/src/clint.py
+++ b/src/clint.py
@@ -909,7 +909,6 @@ def CheckIncludes(filename, lines, error):
             "src/nvim/buffer_defs.h",
             "src/nvim/channel.h",
             "src/nvim/charset.h",
-            "src/nvim/cmdexpand.h",
             "src/nvim/decoration.h",
             "src/nvim/drawline.h",
             "src/nvim/eval.h",
@@ -930,7 +929,6 @@ def CheckIncludes(filename, lines, error):
             "src/nvim/event/wstream.h",
             "src/nvim/extmark.h",
             "src/nvim/garray.h",
-            "src/nvim/getchar.h",
             "src/nvim/globals.h",
             "src/nvim/grid.h",
             "src/nvim/highlight.h",
@@ -945,7 +943,6 @@ def CheckIncludes(filename, lines, error):
             "src/nvim/msgpack_rpc/helpers.h",
             "src/nvim/msgpack_rpc/unpacker.h",
             "src/nvim/option.h",
-            "src/nvim/os/fileio.h",
             "src/nvim/os/input.h",
             "src/nvim/os/pty_conpty_win.h",
             "src/nvim/os/pty_process_unix.h",
diff --git a/src/nvim/cmdexpand.h b/src/nvim/cmdexpand.h
index b0772d26a3..a45b334cfb 100644
--- a/src/nvim/cmdexpand.h
+++ b/src/nvim/cmdexpand.h
@@ -2,8 +2,9 @@
 
 #include "nvim/cmdexpand_defs.h"  // IWYU pragma: export
 #include "nvim/eval/typval_defs.h"  // IWYU pragma: keep
-#include "nvim/ex_getln.h"
+#include "nvim/ex_getln_defs.h"  // IWYU pragma: keep
 #include "nvim/garray_defs.h"  // IWYU pragma: keep
+#include "nvim/regexp_defs.h"  // IWYU pragma: keep
 #include "nvim/types_defs.h"  // IWYU pragma: keep
 
 // Values for nextwild() and ExpandOne().  See ExpandOne() for meaning.
diff --git a/src/nvim/eval.h b/src/nvim/eval.h
index 7306645cc3..6d225b2713 100644
--- a/src/nvim/eval.h
+++ b/src/nvim/eval.h
@@ -13,8 +13,8 @@
 #include "nvim/hashtab_defs.h"
 #include "nvim/macros_defs.h"
 #include "nvim/mbyte_defs.h"  // IWYU pragma: keep
-#include "nvim/os/fileio.h"
-#include "nvim/os/stdpaths_defs.h"
+#include "nvim/os/fileio_defs.h"  // IWYU pragma: keep
+#include "nvim/os/stdpaths_defs.h"  // IWYU pragma: keep
 #include "nvim/vim_defs.h"  // IWYU pragma: keep
 
 #define COPYID_INC 2
diff --git a/src/nvim/event/stream.h b/src/nvim/event/stream.h
index d02707dc45..ab694e2247 100644
--- a/src/nvim/event/stream.h
+++ b/src/nvim/event/stream.h
@@ -6,7 +6,7 @@
 
 #include "nvim/event/loop.h"
 #include "nvim/event/multiqueue.h"
-#include "nvim/rbuffer.h"
+#include "nvim/rbuffer_defs.h"
 
 struct stream;
 
diff --git a/src/nvim/ex_getln.h b/src/nvim/ex_getln.h
index 93bdd2299f..af08970f0b 100644
--- a/src/nvim/ex_getln.h
+++ b/src/nvim/ex_getln.h
@@ -1,76 +1,13 @@
 #pragma once
 
-#include <stdbool.h>
+#include <stddef.h>  // IWYU pragma: keep
 
-#include "klib/kvec.h"
-#include "nvim/cmdexpand_defs.h"
-#include "nvim/eval/typval_defs.h"
+#include "nvim/eval/typval_defs.h"  // IWYU pragma: keep
 #include "nvim/ex_cmds_defs.h"  // IWYU pragma: keep
+#include "nvim/ex_getln_defs.h"  // IWYU pragma: export
 #include "nvim/option_defs.h"  // IWYU pragma: keep
 #include "nvim/types_defs.h"  // IWYU pragma: keep
 
-/// Command-line colors: one chunk
-///
-/// Defines a region which has the same highlighting.
-typedef struct {
-  int start;  ///< Colored chunk start.
-  int end;  ///< Colored chunk end (exclusive, > start).
-  int attr;  ///< Highlight attr.
-} CmdlineColorChunk;
-
-/// Command-line colors
-///
-/// Holds data about all colors.
-typedef kvec_t(CmdlineColorChunk) CmdlineColors;
-
-/// Command-line coloring
-///
-/// Holds both what are the colors and what have been colored. Latter is used to
-/// suppress unnecessary calls to coloring callbacks.
-typedef struct {
-  unsigned prompt_id;  ///< ID of the prompt which was colored last.
-  char *cmdbuff;  ///< What exactly was colored last time or NULL.
-  CmdlineColors colors;  ///< Last colors.
-} ColoredCmdline;
-
-/// Keeps track how much state must be sent to external ui.
-typedef enum {
-  kCmdRedrawNone,
-  kCmdRedrawPos,
-  kCmdRedrawAll,
-} CmdRedraw;
-
-/// Variables shared between getcmdline(), redrawcmdline() and others.
-/// These need to be saved when using CTRL-R |, that's why they are in a
-/// structure.
-typedef struct cmdline_info CmdlineInfo;
-struct cmdline_info {
-  char *cmdbuff;                ///< pointer to command line buffer
-  int cmdbufflen;               ///< length of cmdbuff
-  int cmdlen;                   ///< number of chars in command line
-  int cmdpos;                   ///< current cursor position
-  int cmdspos;                  ///< cursor column on screen
-  int cmdfirstc;                ///< ':', '/', '?', '=', '>' or NUL
-  int cmdindent;                ///< number of spaces before cmdline
-  char *cmdprompt;              ///< message in front of cmdline
-  int cmdattr;                  ///< attributes for prompt
-  int overstrike;               ///< Typing mode on the command line.  Shared by
-                                ///< getcmdline() and put_on_cmdline().
-  expand_T *xpc;                ///< struct being used for expansion, xp_pattern
-                                ///< may point into cmdbuff
-  int xp_context;               ///< type of expansion
-  char *xp_arg;                 ///< user-defined expansion arg
-  int input_fn;                 ///< when true Invoked for input() function
-  unsigned prompt_id;           ///< Prompt number, used to disable coloring on errors.
-  Callback highlight_callback;  ///< Callback used for coloring user input.
-  ColoredCmdline last_colors;   ///< Last cmdline colors
-  int level;                    ///< current cmdline level
-  CmdlineInfo *prev_ccline;     ///< pointer to saved cmdline state
-  char special_char;            ///< last putcmdline char (used for redraws)
-  bool special_shift;           ///< shift of last putcmdline char
-  CmdRedraw redraw_state;       ///< needed redraw for external cmdline
-};
-
 /// flags used by vim_strsave_fnameescape()
 enum {
   VSE_NONE   = 0,
diff --git a/src/nvim/ex_getln_defs.h b/src/nvim/ex_getln_defs.h
new file mode 100644
index 0000000000..daba6cabb8
--- /dev/null
+++ b/src/nvim/ex_getln_defs.h
@@ -0,0 +1,68 @@
+#pragma once
+
+#include <stdbool.h>
+
+#include "klib/kvec.h"
+#include "nvim/cmdexpand_defs.h"
+
+/// Command-line colors: one chunk
+///
+/// Defines a region which has the same highlighting.
+typedef struct {
+  int start;  ///< Colored chunk start.
+  int end;  ///< Colored chunk end (exclusive, > start).
+  int attr;  ///< Highlight attr.
+} CmdlineColorChunk;
+
+/// Command-line colors
+///
+/// Holds data about all colors.
+typedef kvec_t(CmdlineColorChunk) CmdlineColors;
+
+/// Command-line coloring
+///
+/// Holds both what are the colors and what have been colored. Latter is used to
+/// suppress unnecessary calls to coloring callbacks.
+typedef struct {
+  unsigned prompt_id;  ///< ID of the prompt which was colored last.
+  char *cmdbuff;  ///< What exactly was colored last time or NULL.
+  CmdlineColors colors;  ///< Last colors.
+} ColoredCmdline;
+
+/// Keeps track how much state must be sent to external ui.
+typedef enum {
+  kCmdRedrawNone,
+  kCmdRedrawPos,
+  kCmdRedrawAll,
+} CmdRedraw;
+
+/// Variables shared between getcmdline(), redrawcmdline() and others.
+/// These need to be saved when using CTRL-R |, that's why they are in a
+/// structure.
+typedef struct cmdline_info CmdlineInfo;
+struct cmdline_info {
+  char *cmdbuff;                ///< pointer to command line buffer
+  int cmdbufflen;               ///< length of cmdbuff
+  int cmdlen;                   ///< number of chars in command line
+  int cmdpos;                   ///< current cursor position
+  int cmdspos;                  ///< cursor column on screen
+  int cmdfirstc;                ///< ':', '/', '?', '=', '>' or NUL
+  int cmdindent;                ///< number of spaces before cmdline
+  char *cmdprompt;              ///< message in front of cmdline
+  int cmdattr;                  ///< attributes for prompt
+  int overstrike;               ///< Typing mode on the command line.  Shared by
+                                ///< getcmdline() and put_on_cmdline().
+  expand_T *xpc;                ///< struct being used for expansion, xp_pattern
+                                ///< may point into cmdbuff
+  int xp_context;               ///< type of expansion
+  char *xp_arg;                 ///< user-defined expansion arg
+  int input_fn;                 ///< when true Invoked for input() function
+  unsigned prompt_id;           ///< Prompt number, used to disable coloring on errors.
+  Callback highlight_callback;  ///< Callback used for coloring user input.
+  ColoredCmdline last_colors;   ///< Last cmdline colors
+  int level;                    ///< current cmdline level
+  CmdlineInfo *prev_ccline;     ///< pointer to saved cmdline state
+  char special_char;            ///< last putcmdline char (used for redraws)
+  bool special_shift;           ///< shift of last putcmdline char
+  CmdRedraw redraw_state;       ///< needed redraw for external cmdline
+};
diff --git a/src/nvim/getchar.h b/src/nvim/getchar.h
index e1bc64bfee..6e41bef298 100644
--- a/src/nvim/getchar.h
+++ b/src/nvim/getchar.h
@@ -1,11 +1,11 @@
 #pragma once
 
-#include <stdbool.h>
-#include <stdint.h>
+#include <stddef.h>  // IWYU pragma: keep
+#include <stdint.h>  // IWYU pragma: keep
 
 #include "nvim/eval/typval_defs.h"  // IWYU pragma: keep
 #include "nvim/getchar_defs.h"  // IWYU pragma: export
-#include "nvim/os/fileio.h"
+#include "nvim/os/fileio_defs.h"
 #include "nvim/types_defs.h"  // IWYU pragma: keep
 
 /// Argument for flush_buffers().
diff --git a/src/nvim/os/fileio.h b/src/nvim/os/fileio.h
index 72e7984c8a..55f213f377 100644
--- a/src/nvim/os/fileio.h
+++ b/src/nvim/os/fileio.h
@@ -1,20 +1,8 @@
 #pragma once
 
-#include <stdbool.h>
-#include <stddef.h>
+#include <stddef.h>  // IWYU pragma: keep
 
-#include "nvim/func_attr.h"
-#include "nvim/rbuffer.h"
-
-/// Structure used to read from/write to file
-typedef struct {
-  int fd;  ///< File descriptor.
-  int _error;  ///< Error code for use with RBuffer callbacks or zero.
-  RBuffer *rv;  ///< Read or write buffer.
-  bool wr;  ///< True if file is in write mode.
-  bool eof;  ///< True if end of file was encountered.
-  bool non_blocking;  ///< True if EAGAIN should not restart syscalls.
-} FileDescriptor;
+#include "nvim/os/fileio_defs.h"  // IWYU pragma: export
 
 /// file_open() flags
 typedef enum {
@@ -37,33 +25,6 @@ typedef enum {
   kFileMkDir = 256,
 } FileOpenFlags;
 
-static inline bool file_eof(const FileDescriptor *fp)
-  REAL_FATTR_PURE REAL_FATTR_WARN_UNUSED_RESULT REAL_FATTR_NONNULL_ALL;
-
-/// Check whether end of file was encountered
-///
-/// @param[in]  fp  File to check.
-///
-/// @return true if it was, false if it was not or read operation was never
-///         performed.
-static inline bool file_eof(const FileDescriptor *const fp)
-{
-  return fp->eof && rbuffer_size(fp->rv) == 0;
-}
-
-static inline int file_fd(const FileDescriptor *fp)
-  REAL_FATTR_PURE REAL_FATTR_WARN_UNUSED_RESULT REAL_FATTR_NONNULL_ALL;
-
-/// Return the file descriptor associated with the FileDescriptor structure
-///
-/// @param[in]  fp  File to check.
-///
-/// @return File descriptor.
-static inline int file_fd(const FileDescriptor *const fp)
-{
-  return fp->fd;
-}
-
 enum {
   /// Read or write buffer size
   ///
diff --git a/src/nvim/os/fileio_defs.h b/src/nvim/os/fileio_defs.h
new file mode 100644
index 0000000000..3dc8c7b22a
--- /dev/null
+++ b/src/nvim/os/fileio_defs.h
@@ -0,0 +1,43 @@
+#pragma once
+
+#include <stdbool.h>
+
+#include "nvim/func_attr.h"
+#include "nvim/rbuffer_defs.h"
+
+/// Structure used to read from/write to file
+typedef struct {
+  int fd;             ///< File descriptor.
+  int _error;         ///< Error code for use with RBuffer callbacks or zero.
+  RBuffer *rv;        ///< Read or write buffer.
+  bool wr;            ///< True if file is in write mode.
+  bool eof;           ///< True if end of file was encountered.
+  bool non_blocking;  ///< True if EAGAIN should not restart syscalls.
+} FileDescriptor;
+
+static inline bool file_eof(const FileDescriptor *fp)
+  REAL_FATTR_ALWAYS_INLINE REAL_FATTR_WARN_UNUSED_RESULT REAL_FATTR_NONNULL_ALL;
+
+/// Check whether end of file was encountered
+///
+/// @param[in]  fp  File to check.
+///
+/// @return true if it was, false if it was not or read operation was never
+///         performed.
+static inline bool file_eof(const FileDescriptor *const fp)
+{
+  return fp->eof && rbuffer_size(fp->rv) == 0;
+}
+
+static inline int file_fd(const FileDescriptor *fp)
+  REAL_FATTR_ALWAYS_INLINE REAL_FATTR_WARN_UNUSED_RESULT REAL_FATTR_NONNULL_ALL;
+
+/// Return the file descriptor associated with the FileDescriptor structure
+///
+/// @param[in]  fp  File to check.
+///
+/// @return File descriptor.
+static inline int file_fd(const FileDescriptor *const fp)
+{
+  return fp->fd;
+}
diff --git a/src/nvim/rbuffer.c b/src/nvim/rbuffer.c
index aff06ee31b..d2fae5388f 100644
--- a/src/nvim/rbuffer.c
+++ b/src/nvim/rbuffer.c
@@ -29,27 +29,12 @@ RBuffer *rbuffer_new(size_t capacity)
   return rv;
 }
 
-void rbuffer_free(RBuffer *buf)
+void rbuffer_free(RBuffer *buf) FUNC_ATTR_NONNULL_ALL
 {
   xfree(buf->temp);
   xfree(buf);
 }
 
-size_t rbuffer_size(RBuffer *buf) FUNC_ATTR_NONNULL_ALL
-{
-  return buf->size;
-}
-
-size_t rbuffer_capacity(RBuffer *buf) FUNC_ATTR_NONNULL_ALL
-{
-  return (size_t)(buf->end_ptr - buf->start_ptr);
-}
-
-size_t rbuffer_space(RBuffer *buf) FUNC_ATTR_NONNULL_ALL
-{
-  return rbuffer_capacity(buf) - buf->size;
-}
-
 /// Return a pointer to a raw buffer containing the first empty slot available
 /// for writing. The second argument is a pointer to the maximum number of
 /// bytes that could be written.
diff --git a/src/nvim/rbuffer.h b/src/nvim/rbuffer.h
index 55e9849d3d..78483b2a50 100644
--- a/src/nvim/rbuffer.h
+++ b/src/nvim/rbuffer.h
@@ -16,6 +16,8 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#include "nvim/rbuffer_defs.h"  // IWYU pragma: export
+
 // Macros that simplify working with the read/write pointers directly by hiding
 // ring buffer wrap logic. Some examples:
 //
@@ -64,22 +66,6 @@
        i-- > 0 ? ((int)(c = *rbuffer_get(buf, i))) || 1 : 0; \
        )
 
-typedef struct rbuffer RBuffer;
-/// Type of function invoked during certain events:
-///   - When the RBuffer switches to the full state
-///   - When the RBuffer switches to the non-full state
-typedef void (*rbuffer_callback)(RBuffer *buf, void *data);
-
-struct rbuffer {
-  rbuffer_callback full_cb, nonfull_cb;
-  void *data;
-  size_t size;
-  // helper memory used to by rbuffer_reset if required
-  char *temp;
-  char *end_ptr, *read_ptr, *write_ptr;
-  char start_ptr[];
-};
-
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "rbuffer.h.generated.h"
 #endif
diff --git a/src/nvim/rbuffer_defs.h b/src/nvim/rbuffer_defs.h
new file mode 100644
index 0000000000..51dc349846
--- /dev/null
+++ b/src/nvim/rbuffer_defs.h
@@ -0,0 +1,45 @@
+#pragma once
+
+#include <stddef.h>
+
+#include "nvim/func_attr.h"
+
+typedef struct rbuffer RBuffer;
+/// Type of function invoked during certain events:
+///   - When the RBuffer switches to the full state
+///   - When the RBuffer switches to the non-full state
+typedef void (*rbuffer_callback)(RBuffer *buf, void *data);
+
+struct rbuffer {
+  rbuffer_callback full_cb, nonfull_cb;
+  void *data;
+  size_t size;
+  // helper memory used to by rbuffer_reset if required
+  char *temp;
+  char *end_ptr, *read_ptr, *write_ptr;
+  char start_ptr[];
+};
+
+static inline size_t rbuffer_size(RBuffer *buf)
+  REAL_FATTR_ALWAYS_INLINE REAL_FATTR_NONNULL_ALL;
+
+static inline size_t rbuffer_size(RBuffer *buf)
+{
+  return buf->size;
+}
+
+static inline size_t rbuffer_capacity(RBuffer *buf)
+  REAL_FATTR_ALWAYS_INLINE REAL_FATTR_NONNULL_ALL;
+
+static inline size_t rbuffer_capacity(RBuffer *buf)
+{
+  return (size_t)(buf->end_ptr - buf->start_ptr);
+}
+
+static inline size_t rbuffer_space(RBuffer *buf)
+  REAL_FATTR_ALWAYS_INLINE REAL_FATTR_NONNULL_ALL;
+
+static inline size_t rbuffer_space(RBuffer *buf)
+{
+  return rbuffer_capacity(buf) - buf->size;
+}
diff --git a/src/nvim/tui/input.c b/src/nvim/tui/input.c
index b9e2d2c9ee..1e14f3fee9 100644
--- a/src/nvim/tui/input.c
+++ b/src/nvim/tui/input.c
@@ -13,6 +13,7 @@
 #include "nvim/memory.h"
 #include "nvim/option_vars.h"
 #include "nvim/os/os.h"
+#include "nvim/rbuffer.h"
 #include "nvim/strings.h"
 #include "nvim/tui/input.h"
 #include "nvim/tui/input_defs.h"
diff --git a/src/nvim/tui/input.h b/src/nvim/tui/input.h
index 27a0291f5b..9d276277de 100644
--- a/src/nvim/tui/input.h
+++ b/src/nvim/tui/input.h
@@ -7,7 +7,7 @@
 #include "nvim/event/loop.h"
 #include "nvim/event/stream.h"
 #include "nvim/event/time.h"
-#include "nvim/rbuffer.h"
+#include "nvim/rbuffer_defs.h"
 #include "nvim/tui/input_defs.h"  // IWYU pragma: export
 #include "nvim/tui/tui.h"
 #include "nvim/types_defs.h"