refactor: add pure attribute to pure functions

This will allow compilers that support the pure attribute to make
further optimizations to functions.

src/nvim/arabic.c

@@ -974,6 +974,7 @@ int arabic_shape(int c, int *ccp, int *c1p, int prev_c, int prev_c1, int next_c)
 /// @param one First character.
 /// @param two Character just after "one".
 bool arabic_combine(int one, int two)
+  FUNC_ATTR_PURE
 {
   if (one == a_LAM) {
     return arabic_maycombine(two);
@@ -984,6 +985,7 @@ bool arabic_combine(int one, int two)
 /// Check whether we are dealing with a character that could be regarded as an
 /// Arabic combining character, need to check the character before this.
 bool arabic_maycombine(int two)
+  FUNC_ATTR_PURE
 {
   if (p_arshape && !p_tbidi) {
     return two == a_ALEF_MADDA

src/nvim/autocmd.c

@@ -379,6 +379,7 @@ static void au_cleanup(void)
 
 // Get the first AutoPat for a particular event.
 AutoPat *au_get_autopat_for_event(event_T event)
+  FUNC_ATTR_PURE
 {
   return first_autopat[(int)event];
 }
@@ -1143,6 +1144,7 @@ int autocmd_register(int64_t id, event_T event, char_u *pat, int patlen, int gro
 }
 
 size_t aucmd_pattern_length(char_u *pat)
+  FUNC_ATTR_PURE
 {
   if (*pat == NUL) {
     return 0;
@@ -1175,6 +1177,7 @@ size_t aucmd_pattern_length(char_u *pat)
 }
 
 char_u *aucmd_next_pattern(char_u *pat, size_t patlen)
+  FUNC_ATTR_PURE
 {
   pat = pat + patlen;
   if (*pat == ',') {
@@ -2383,6 +2386,7 @@ theend:
 
 // Checks if a pattern is buflocal
 bool aupat_is_buflocal(char_u *pat, int patlen)
+  FUNC_ATTR_PURE
 {
   return patlen >= 8
          && STRNCMP(pat, "<buffer", 7) == 0
@@ -2492,6 +2496,7 @@ char *aucmd_exec_default_desc(AucmdExecutable acc)
 }
 
 char *aucmd_exec_to_string(AutoCmd *ac, AucmdExecutable acc)
+  FUNC_ATTR_PURE
 {
   switch (acc.type) {
   case CALLABLE_EX:
@@ -2542,6 +2547,7 @@ AucmdExecutable aucmd_exec_copy(AucmdExecutable src)
 }
 
 bool aucmd_exec_is_deleted(AucmdExecutable acc)
+  FUNC_ATTR_PURE
 {
   switch (acc.type) {
   case CALLABLE_EX:
@@ -2556,6 +2562,7 @@ bool aucmd_exec_is_deleted(AucmdExecutable acc)
 }
 
 bool au_event_is_empty(event_T event)
+  FUNC_ATTR_PURE
 {
   return first_autopat[event] == NULL;
 }

src/nvim/buffer_updates.c

@@ -84,6 +84,7 @@ bool buf_updates_register(buf_T *buf, uint64_t channel_id, BufUpdateCallbacks cb
 }
 
 bool buf_updates_active(buf_T *buf)
+  FUNC_ATTR_PURE
 {
   return kv_size(buf->update_channels) || kv_size(buf->update_callbacks);
 }

src/nvim/context.c

@@ -33,6 +33,7 @@ void ctx_free_all(void)
 
 /// Returns the size of the context stack.
 size_t ctx_size(void)
+  FUNC_ATTR_PURE
 {
   return kv_size(ctx_stack);
 }
@@ -40,6 +41,7 @@ size_t ctx_size(void)
 /// Returns pointer to Context object with given zero-based index from the top
 /// of context stack or NULL if index is out of bounds.
 Context *ctx_get(size_t index)
+  FUNC_ATTR_PURE
 {
   if (index < kv_size(ctx_stack)) {
     return &kv_Z(ctx_stack, index);

src/nvim/cursor_shape.c

@@ -277,6 +277,7 @@ char *parse_shape_opt(int what)
 ///
 /// @param exclusive If 'selection' option is "exclusive".
 bool cursor_is_block_during_visual(bool exclusive)
+  FUNC_ATTR_PURE
 {
   int mode_idx = exclusive ? SHAPE_IDX_VE : SHAPE_IDX_V;
   return (SHAPE_BLOCK == shape_table[mode_idx].shape
@@ -300,6 +301,7 @@ int cursor_mode_str2int(const char *mode)
 
 /// Check if a syntax id is used as a cursor style.
 bool cursor_mode_uses_syn_id(int syn_id)
+  FUNC_ATTR_PURE
 {
   if (*p_guicursor == NUL) {
     return false;
@@ -316,6 +318,7 @@ bool cursor_mode_uses_syn_id(int syn_id)
 
 /// Return the index into shape_table[] for the current mode.
 int cursor_get_mode_idx(void)
+  FUNC_ATTR_PURE
 {
   if (State == SHOWMATCH) {
     return SHAPE_IDX_SM;

src/nvim/diff.c

@@ -883,6 +883,7 @@ theend:
 /// diff will be used anyway.
 ///
 int diff_internal(void)
+  FUNC_ATTR_PURE
 {
   return (diff_flags & DIFF_INTERNAL) != 0 && *p_dex == NUL;
 }
@@ -2250,6 +2251,7 @@ bool diffopt_horizontal(void)
 
 // Return true if 'diffopt' contains "hiddenoff".
 bool diffopt_hiddenoff(void)
+  FUNC_ATTR_PURE
 {
   return (diff_flags & DIFF_HIDDEN_OFF) != 0;
 }

src/nvim/digraph.c

@@ -1551,6 +1551,7 @@ int get_digraph(bool cmdline)
 /// @return If no match, return "char2". If "meta_char" is true and "char1"
 //          is a space, return "char2" | 0x80.
 static int getexactdigraph(int char1, int char2, bool meta_char)
+  FUNC_ATTR_PURE
 {
   int retval = 0;
 
@@ -1601,6 +1602,7 @@ static int getexactdigraph(int char1, int char2, bool meta_char)
 ///
 /// @return The digraph.
 int digraph_get(int char1, int char2, bool meta_char)
+  FUNC_ATTR_PURE
 {
   int retval;
 

src/nvim/ex_getln.c

@@ -2604,6 +2604,7 @@ char_u *getexline(int c, void *cookie, int indent, bool do_concat)
 }
 
 bool cmdline_overstrike(void)
+  FUNC_ATTR_PURE
 {
   return ccline.overstrike;
 }
@@ -2611,6 +2612,7 @@ bool cmdline_overstrike(void)
 
 /// Return true if the cursor is at the end of the cmdline.
 bool cmdline_at_end(void)
+  FUNC_ATTR_PURE
 {
   return (ccline.cmdpos >= ccline.cmdlen);
 }