Handling of CamelCase in the spell checker

The problem is that my source code has a lot of camel case identifiers,
dictated by our coding standard. I want to use the spell checker but
it marks every camel case identifier as a miss-spelled word.

This is a simple patch to the spell checking that interprets a lower
case letter followed by an uppercase as a word boundary.

Change-Id: I6f581d0bd15f2a41787df8db6853bd4d3db92913

runtime/doc/options.txt

@@ -6863,6 +6863,16 @@ A jump table for the options with a short description can be found at |Q_op|.
 	When on spell checking will be done.  See |spell|.
 	The languages are specified with 'spelllang'.
 
+						*'spellcamelcase'* *'scc'*
+						*'nospellcamelcase'* *'noscc'*
+'spellcamelcase'	boolean	(default off)
+			local to window
+			{not in Vi}
+			{not available when compiled without the |+syntax|
+			feature}
+	When on spell checking will treat each word in a camelCase identifier
+	as a distinct word.
+
 						*'spellcapcheck'* *'spc'*
 'spellcapcheck' 'spc'	string	(default "[.?!]\_[\])'" \t]\+")
 			local to buffer

src/option.c

@@ -231,6 +231,7 @@
 #define PV_SCROLL	OPT_WIN(WV_SCROLL)
 #ifdef FEAT_SPELL
 # define PV_SPELL	OPT_WIN(WV_SPELL)
+# define PV_SCC		OPT_WIN(WV_SCC)
 #endif
 #ifdef FEAT_SYN_HL
 # define PV_CUC		OPT_WIN(WV_CUC)
@@ -2456,6 +2457,13 @@ static struct vimoption options[] =
 			    (char_u *)VAR_WIN, PV_SPELL,
 #else
 			    (char_u *)NULL, PV_NONE,
+#endif
+			    {(char_u *)FALSE, (char_u *)0L} SCRIPTID_INIT},
+    {"spellcamelcase", "scc", P_BOOL|P_VI_DEF|P_RWIN,
+#ifdef FEAT_SPELL
+			    (char_u *)VAR_WIN, PV_SCC,
+#else
+			    (char_u *)NULL, PV_NONE,
 #endif
 			    {(char_u *)FALSE, (char_u *)0L} SCRIPTID_INIT},
     {"spellcapcheck", "spc", P_STRING|P_ALLOCED|P_VI_DEF|P_RBUF,
@@ -10331,6 +10339,7 @@ get_varp(struct vimoption *p)
 	case PV_LIST:	return (char_u *)&(curwin->w_p_list);
 #ifdef FEAT_SPELL
 	case PV_SPELL:	return (char_u *)&(curwin->w_p_spell);
+	case PV_SCC:	return (char_u *)&(curwin->w_p_scc);
 #endif
 #ifdef FEAT_SYN_HL
 	case PV_CUC:	return (char_u *)&(curwin->w_p_cuc);

src/option.h

@@ -1165,6 +1165,7 @@ enum
     , WV_SCROLL
 #ifdef FEAT_SPELL
     , WV_SPELL
+    , WV_SCC
 #endif
 #ifdef FEAT_SYN_HL
     , WV_CUC

src/spell.c

@@ -435,6 +435,7 @@ spell_check(
     int		wrongcaplen = 0;
     int		lpi;
     int		count_word = docount;
+    int		camel_case = 0;
 
     /* A word never starts at a space or a control character.  Return quickly
      * then, skipping over the character. */
@@ -466,10 +467,15 @@ spell_check(
     mi.mi_fend = ptr;
     if (spell_iswordp(mi.mi_fend, wp))
     {
+	int last_char_upper;
+	int this_char_upper = SPELL_ISUPPER(*mi.mi_fend);
 	do
 	{
+	    last_char_upper = this_char_upper;
 	    mb_ptr_adv(mi.mi_fend);
-	} while (*mi.mi_fend != NUL && spell_iswordp(mi.mi_fend, wp));
+	    this_char_upper = SPELL_ISUPPER(*mi.mi_fend);
+	    camel_case = wp->w_p_scc && !last_char_upper && this_char_upper;
+	} while (*mi.mi_fend != NUL && spell_iswordp(mi.mi_fend, wp) && !camel_case);
 
 	if (capcol != NULL && *capcol == 0 && wp->w_s->b_cap_prog != NULL)
 	{
@@ -500,6 +506,12 @@ spell_check(
 							     MAXWLEN + 1);
     mi.mi_fwordlen = (int)STRLEN(mi.mi_fword);
 
+    // Introduce a fake word end space into the folded word if the word is camel case
+    if (camel_case)
+    {
+	mi.mi_fword[mi.mi_fwordlen-1] = ' ';
+    }
+
     /* The word is bad unless we recognize it. */
     mi.mi_result = SP_BAD;
     mi.mi_result2 = SP_BAD;

src/structs.h

@@ -223,6 +223,8 @@ typedef struct
 #ifdef FEAT_SPELL
     int		wo_spell;
 # define w_p_spell w_onebuf_opt.wo_spell /* 'spell' */
+    int		wo_scc;
+# define w_p_scc w_onebuf_opt.wo_scc	/* 'spellcamelcase' */
 #endif
 #ifdef FEAT_SYN_HL
     int		wo_cuc;