ga_growsize should be >= 1

I know it could be 0 sometimes. Running the tests with
`assert(gap->ga_growsize > 0)` in ga_grow() crashes nvim while running the
tests.

 - Add a setter for ga_growsize that checks whether the value passed is >=1 (log
	 in case it's not)
 - log when ga_grow() tries to use a ga_growsize that's not >=1
 - use GA_EMPTY_INIT_VALUE is many places

src/nvim/ex_cmds2.c

@@ -2790,7 +2790,7 @@ char_u *getsourceline(int c, void *cookie, int indent)
         /* Adjust the growsize to the current length to speed up
          * concatenating many lines. */
         if (ga.ga_len > 400) {
-          ga.ga_growsize = (ga.ga_len > 8000) ? 8000 : ga.ga_len;
+          ga_set_growsize(&ga, (ga.ga_len > 8000) ? 8000 : ga.ga_len);
         }
         ga_concat(&ga, p + 1);
       }

src/nvim/garray.c

@@ -6,6 +6,7 @@
 
 #include "nvim/vim.h"
 #include "nvim/ascii.h"
+#include "nvim/log.h"
 #include "nvim/misc2.h"
 #include "nvim/memory.h"
 #include "nvim/path.h"
@@ -52,7 +53,21 @@ void ga_init(garray_T *gap, int itemsize, int growsize)
   gap->ga_maxlen = 0;
   gap->ga_len = 0;
   gap->ga_itemsize = itemsize;
-  gap->ga_growsize = growsize;
+  ga_set_growsize(gap, growsize);
+}
+
+/// A setter for the growsize that guarantees it will be at least 1.
+///
+/// @param gap
+/// @param growsize
+void ga_set_growsize(garray_T *gap, int growsize)
+{
+  if (growsize < 1) {
+    WLOG("trying to set an invalid ga_growsize: %d", growsize);
+    gap->ga_growsize = 1;
+  } else {
+    gap->ga_growsize = growsize;
+  }
 }
 
 /// Make room in growing array "gap" for at least "n" items.
@@ -66,17 +81,24 @@ void ga_grow(garray_T *gap, int n)
     return;
   }
 
-  // the garray grows by at least growsize (do we have a MIN macro somewhere?)
-  n = (n < gap->ga_growsize) ? gap->ga_growsize : n;
+  if (gap->ga_growsize < 1) {
+    WLOG("ga_growsize(%d) is less than 1", gap->ga_growsize);
+  }
 
-  size_t new_size = (size_t)(gap->ga_itemsize * (gap->ga_len + n));
+  // the garray grows by at least growsize
+  if (n < gap->ga_growsize) {
+    n = gap->ga_growsize;
+  }
+  int new_maxlen = gap->ga_len + n;
+
+  size_t new_size = (size_t)(gap->ga_itemsize * new_maxlen);
   size_t old_size = (size_t)(gap->ga_itemsize * gap->ga_maxlen);
 
   // reallocate and clear the new memory
-  char_u *pp = xrealloc(gap->ga_data, new_size);
+  char *pp = xrealloc(gap->ga_data, new_size);
   memset(pp + old_size, 0, new_size - old_size);
 
-  gap->ga_maxlen = gap->ga_len + n;
+  gap->ga_maxlen = new_maxlen;
   gap->ga_data = pp;
 }
 

src/nvim/garray.h

@@ -12,7 +12,7 @@ typedef struct growarray {
   void *ga_data;                    // pointer to the first item
 } garray_T;
 
-#define GA_EMPTY_INIT_VALUE { 0, 0, 0, 0, NULL }
+#define GA_EMPTY_INIT_VALUE { 0, 0, 0, 1, NULL }
 
 #define GA_EMPTY(ga_ptr) ((ga_ptr)->ga_len <= 0)
 

src/nvim/globals.h

@@ -969,7 +969,7 @@ EXTERN int need_cursor_line_redraw INIT(= FALSE);
 /* Grow array to collect error messages in until they can be displayed. */
 EXTERN garray_T error_ga
 # ifdef DO_INIT
-  = {0, 0, 0, 0, NULL}
+  = GA_EMPTY_INIT_VALUE
 # endif
 ;
 #endif

src/nvim/hardcopy.c

@@ -1285,7 +1285,7 @@ static int prt_collate;
  * Buffers used when generating PostScript output
  */
 static char_u prt_line_buffer[257];
-static garray_T prt_ps_buffer;
+static garray_T prt_ps_buffer = GA_EMPTY_INIT_VALUE;
 
 static int prt_do_conv;
 static vimconv_T prt_conv;

src/nvim/menu.c

@@ -1434,7 +1434,7 @@ typedef struct {
   char_u      *to;              /* translated name */
 } menutrans_T;
 
-static garray_T menutrans_ga = {0, 0, 0, 0, NULL};
+static garray_T menutrans_ga = GA_EMPTY_INIT_VALUE;
 
 /*
  * ":menutrans".

src/nvim/message.c

@@ -2257,8 +2257,8 @@ void mch_errmsg(char *str)
   emsg_on_display = FALSE;
 
   len = (int)STRLEN(str) + 1;
-  if (error_ga.ga_growsize == 0) {
-    error_ga.ga_growsize = 80;
+  if (error_ga.ga_data == NULL) {
+    ga_set_growsize(&error_ga, 80);
     error_ga.ga_itemsize = 1;
   }
   ga_grow(&error_ga, len);

src/nvim/misc1.c

@@ -58,7 +58,7 @@
 # include "misc1.c.generated.h"
 #endif
 /* All user names (for ~user completion as done by shell). */
-static garray_T ga_users;
+static garray_T ga_users = GA_EMPTY_INIT_VALUE;
 
 /*
  * open_line: Add a new line below or above the current line.

src/nvim/option.c

@@ -7499,7 +7499,7 @@ typedef struct {
   int to;
 } langmap_entry_T;
 
-static garray_T langmap_mapga;
+static garray_T langmap_mapga = GA_EMPTY_INIT_VALUE;
 
 /*
  * Search for an entry in "langmap_mapga" for "from".  If found set the "to"

src/nvim/regexp.c

@@ -3180,8 +3180,8 @@ static int reg_line_lbr;                    /* "\n" in string is line break */
  * or regbehind_T.
  * "backpos_T" is a table with backpos_T for BACK
  */
-static garray_T regstack = {0, 0, 0, 0, NULL};
-static garray_T backpos = {0, 0, 0, 0, NULL};
+static garray_T regstack = GA_EMPTY_INIT_VALUE;
+static garray_T backpos = GA_EMPTY_INIT_VALUE;
 
 /*
  * Both for regstack and backpos tables we use the following strategy of
@@ -3319,13 +3319,13 @@ static long bt_regexec_both(char_u *line,
      * onto the regstack. */
     ga_init(&regstack, 1, REGSTACK_INITIAL);
     ga_grow(&regstack, REGSTACK_INITIAL);
-    regstack.ga_growsize = REGSTACK_INITIAL * 8;
+    ga_set_growsize(&regstack, REGSTACK_INITIAL * 8);
   }
 
   if (backpos.ga_data == NULL) {
     ga_init(&backpos, sizeof(backpos_T), BACKPOS_INITIAL);
     ga_grow(&backpos, BACKPOS_INITIAL);
-    backpos.ga_growsize = BACKPOS_INITIAL * 8;
+    ga_set_growsize(&backpos, BACKPOS_INITIAL * 8);
   }
 
   if (REG_MULTI) {

src/nvim/syntax.c

@@ -75,7 +75,8 @@ struct hl_group {
 #define SG_GUI          4       /* gui has been set */
 #define SG_LINK         8       /* link has been set */
 
-static garray_T highlight_ga;   /* highlight groups for 'highlight' option */
+// highlight groups for 'highlight' option
+static garray_T highlight_ga = GA_EMPTY_INIT_VALUE;
 
 #define HL_TABLE() ((struct hl_group *)((highlight_ga.ga_data)))
 
@@ -360,7 +361,7 @@ static int current_state_stored = 0;      /* TRUE if stored current state
                                            * after setting current_finished */
 static int current_finished = 0;        /* current line has been finished */
 static garray_T current_state           /* current stack of state_items */
-  = {0, 0, 0, 0, NULL};
+  = GA_EMPTY_INIT_VALUE;
 static short    *current_next_list = NULL; /* when non-zero, nextgroup list */
 static int current_next_flags = 0;      /* flags for current_next_list */
 static int current_line_id = 0;         /* unique number for current line */
@@ -1452,7 +1453,7 @@ static void invalidate_current_state(void)
 static void validate_current_state(void)
 {
   current_state.ga_itemsize = sizeof(stateitem_T);
-  current_state.ga_growsize = 3;
+  ga_set_growsize(&current_state, 3);
 }
 
 /*
@@ -4746,7 +4747,7 @@ static int syn_add_cluster(char_u *name)
    */
   if (curwin->w_s->b_syn_clusters.ga_data == NULL) {
     curwin->w_s->b_syn_clusters.ga_itemsize = sizeof(syn_cluster_T);
-    curwin->w_s->b_syn_clusters.ga_growsize = 10;
+    ga_set_growsize(&curwin->w_s->b_syn_clusters, 10);
   }
 
   int len = curwin->w_s->b_syn_clusters.ga_len;
@@ -4846,7 +4847,7 @@ static void syn_cmd_cluster(exarg_T *eap, int syncing)
 static void init_syn_patterns(void)
 {
   curwin->w_s->b_syn_patterns.ga_itemsize = sizeof(synpat_T);
-  curwin->w_s->b_syn_patterns.ga_growsize = 10;
+  ga_set_growsize(&curwin->w_s->b_syn_patterns, 10);
 }
 
 /*
@@ -6731,11 +6732,11 @@ static void highlight_clear(int idx)
  * Note that this table is used by ALL buffers.  This is required because the
  * GUI can redraw at any time for any buffer.
  */
-static garray_T term_attr_table = {0, 0, 0, 0, NULL};
+static garray_T term_attr_table = GA_EMPTY_INIT_VALUE;
 
 #define TERM_ATTR_ENTRY(idx) ((attrentry_T *)term_attr_table.ga_data)[idx]
 
-static garray_T cterm_attr_table = {0, 0, 0, 0, NULL};
+static garray_T cterm_attr_table = GA_EMPTY_INIT_VALUE;
 
 #define CTERM_ATTR_ENTRY(idx) ((attrentry_T *)cterm_attr_table.ga_data)[idx]
 
@@ -6755,7 +6756,7 @@ static int get_attr_entry(garray_T *table, attrentry_T *aep)
    * Init the table, in case it wasn't done yet.
    */
   table->ga_itemsize = sizeof(attrentry_T);
-  table->ga_growsize = 7;
+  ga_set_growsize(table, 7);
 
   /*
    * Try to find an entry with the same specifications.
@@ -7311,7 +7312,7 @@ static int syn_add_group(char_u *name)
    */
   if (highlight_ga.ga_data == NULL) {
     highlight_ga.ga_itemsize = sizeof(struct hl_group);
-    highlight_ga.ga_growsize = 10;
+    ga_set_growsize(&highlight_ga, 10);
   }
 
   if (highlight_ga.ga_len >= MAX_HL_ID) {