patch 8.2.1462: Vim9: string slice not supported yet

Problem:    Vim9: string slice not supported yet.
Solution:   Add support for string slicing.

src/errors.h

@@ -69,7 +69,8 @@ EXTERN char e_const_requires_a_value[]
 	INIT(= N_("E1021: const requires a value"));
 EXTERN char e_type_or_initialization_required[]
 	INIT(= N_("E1022: type or initialization required"));
-// E1023 unused
+EXTERN char e_cannot_slice_dictionary[]
+	INIT(= N_("E1023: cannot slice a dictionary"));
 // E1024 unused
 EXTERN char e_using_rcurly_outside_if_block_scope[]
 	INIT(= N_("E1025: using } outside of a block scope"));

src/eval.c

@@ -3699,7 +3699,14 @@ eval_index(
 	    case VAR_STRING:
 		s = tv_get_string(rettv);
 		len = (long)STRLEN(s);
+		if (in_vim9script())
+		{
 		    if (range)
+			s = string_slice(s, n1, n2);
+		    else
+			s = char_from_string(s, n1);
+		}
+		else if (range)
 		{
 		    // The resulting variable is a substring.  If the indexes
 		    // are out of range the result is empty.
@@ -3718,10 +3725,6 @@ eval_index(
 		    else
 			s = vim_strnsave(s + n1, n2 - n1 + 1);
 		}
-		else if (in_vim9script())
-		{
-		    s = char_from_string(s, n1);
-		}
 		else
 		{
 		    // The resulting variable is a string of a single
@@ -5312,6 +5315,69 @@ char_from_string(char_u *str, varnumber_T index)
     return vim_strnsave(str + nbyte, MB_CPTR2LEN(str + nbyte));
 }
 
+/*
+ * Get the byte index for character index "idx" in string "str" with length
+ * "str_len".
+ * If going over the end return "str_len".
+ * If "idx" is negative count from the end, -1 is the last character.
+ * When going over the start return zero.
+ */
+    static size_t
+char_idx2byte(char_u *str, size_t str_len, varnumber_T idx)
+{
+    varnumber_T nchar = idx;
+    size_t	nbyte = 0;
+
+    if (nchar >= 0)
+    {
+	while (nchar > 0 && nbyte < str_len)
+	{
+	    nbyte += MB_CPTR2LEN(str + nbyte);
+	    --nchar;
+	}
+    }
+    else
+    {
+	nbyte = str_len;
+	while (nchar < 0 && nbyte > 0)
+	{
+	    --nbyte;
+	    nbyte -= mb_head_off(str, str + nbyte);
+	    ++nchar;
+	}
+    }
+    return nbyte;
+}
+
+/*
+ * Return the slice "str[first:last]" using character indexes.
+ * Return NULL when the result is empty.
+ */
+    char_u *
+string_slice(char_u *str, varnumber_T first, varnumber_T last)
+{
+    size_t	    start_byte, end_byte;
+    size_t	    slen;
+
+    if (str == NULL)
+	return NULL;
+    slen = STRLEN(str);
+    start_byte = char_idx2byte(str, slen, first);
+    if (last == -1)
+	end_byte = slen;
+    else
+    {
+	end_byte = char_idx2byte(str, slen, last);
+	if (end_byte < slen)
+	    // end index is inclusive
+	    end_byte += MB_CPTR2LEN(str + end_byte);
+    }
+
+    if (start_byte >= slen || end_byte <= start_byte)
+	return NULL;
+    return vim_strnsave(str + start_byte, end_byte - start_byte);
+}
+
 /*
  * Handle:
  * - expr[expr], expr[expr:expr] subscript

src/proto/eval.pro

@@ -60,6 +60,7 @@ int eval_isnamec(int c);
 int eval_isnamec1(int c);
 int eval_isdictc(int c);
 char_u *char_from_string(char_u *str, varnumber_T index);
+char_u *string_slice(char_u *str, varnumber_T first, varnumber_T last);
 int handle_subscript(char_u **arg, typval_T *rettv, evalarg_T *evalarg, int verbose);
 int item_copy(typval_T *from, typval_T *to, int deep, int copyID);
 void echo_one(typval_T *rettv, int with_space, int *atstart, int *needclr);

src/testdir/test_vim9_disassemble.vim

@@ -971,7 +971,7 @@ def Test_disassemble_concat()
   assert_equal('aabb', ConcatString())
 enddef
 
-def StringIndex(): number
+def StringIndex(): string
   let s = "abcd"
   let res = s[1]
   return res

src/testdir/test_vim9_expr.vim

@@ -2074,7 +2074,7 @@ def Test_expr7_trailing()
   assert_equal(123, d.key)
 enddef
 
-def Test_expr7_subscript()
+def Test_expr7_string_subscript()
   let lines =<< trim END
     let text = 'abcdef'
     assert_equal('', text[-1])
@@ -2094,6 +2094,28 @@ def Test_expr7_subscript()
     assert_equal('f', text[5])
     assert_equal('', text[6])
     assert_equal('', text[999])
+
+    assert_equal('ábçdëf', text[0:-1])
+    assert_equal('ábçdëf', text[0 :-1])
+    assert_equal('ábçdëf', text[0: -1])
+    assert_equal('ábçdëf', text[0 : -1])
+    assert_equal('ábçdëf', text[0
+                  :-1])
+    assert_equal('ábçdëf', text[0:
+                  -1])
+    assert_equal('ábçdëf', text[0 : -1
+                  ])
+    assert_equal('bçdëf', text[1:-1])
+    assert_equal('çdëf', text[2:-1])
+    assert_equal('dëf', text[3:-1])
+    assert_equal('ëf', text[4:-1])
+    assert_equal('f', text[5:-1])
+    assert_equal('', text[6:-1])
+    assert_equal('', text[999:-1])
+
+    assert_equal('ábçd', text[:3])
+    assert_equal('bçdëf', text[1:])
+    assert_equal('ábçdëf', text[:])
   END
   CheckDefSuccess(lines)
   CheckScriptSuccess(['vim9script'] + lines)

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1462,
 /**/
     1461,
 /**/

src/vim9.h

@@ -117,6 +117,7 @@ typedef enum {
     // expression operations
     ISN_CONCAT,
     ISN_STRINDEX,   // [expr] string index
+    ISN_STRSLICE,   // [expr:expr] string slice
     ISN_LISTINDEX,  // [expr] list index
     ISN_SLICE,	    // drop isn_arg.number items from start of list
     ISN_GETITEM,    // push list item, isn_arg.number is the index

src/vim9compile.c

@@ -3068,6 +3068,7 @@ compile_subscript(
 	    garray_T	*stack = &cctx->ctx_type_stack;
 	    type_T	**typep;
 	    vartype_T	vtype;
+	    int		is_slice = FALSE;
 
 	    // list index: list[123]
 	    // dict member: dict[key]
@@ -3082,11 +3083,36 @@ compile_subscript(
 	    *arg = skipwhite(p);
 	    if (may_get_next_line_error(p, arg, cctx) == FAIL)
 		return FAIL;
+	    if (**arg == ':')
+		// missing first index is equal to zero
+		generate_PUSHNR(cctx, 0);
+	    else
+	    {
 		if (compile_expr0(arg, cctx) == FAIL)
 		    return FAIL;
-
 		if (may_get_next_line_error(p, arg, cctx) == FAIL)
 		    return FAIL;
+		*arg = skipwhite(*arg);
+	    }
+	    if (**arg == ':')
+	    {
+		*arg = skipwhite(*arg + 1);
+		if (may_get_next_line_error(p, arg, cctx) == FAIL)
+		    return FAIL;
+		if (**arg == ']')
+		    // missing second index is equal to end of string
+		    generate_PUSHNR(cctx, -1);
+		else
+		{
+		    if (compile_expr0(arg, cctx) == FAIL)
+		    return FAIL;
+		    if (may_get_next_line_error(p, arg, cctx) == FAIL)
+			return FAIL;
+		    *arg = skipwhite(*arg);
+		}
+		is_slice = TRUE;
+	    }
+
 	    if (**arg != ']')
 	    {
 		emsg(_(e_missbrac));
@@ -3098,7 +3124,8 @@ compile_subscript(
 	    // we can use the index value type.
 	    // TODO: If we don't know use an instruction to figure it out at
 	    // runtime.
-	    typep = ((type_T **)stack->ga_data) + stack->ga_len - 2;
+	    typep = ((type_T **)stack->ga_data) + stack->ga_len
+							  - (is_slice ? 3 : 2);
 	    vtype = (*typep)->tt_type;
 	    if (*typep == &t_any)
 	    {
@@ -3109,6 +3136,11 @@ compile_subscript(
 	    }
 	    if (vtype == VAR_DICT)
 	    {
+		if (is_slice)
+		{
+		    emsg(_(e_cannot_slice_dictionary));
+		    return FAIL;
+		}
 		if ((*typep)->tt_type == VAR_DICT)
 		    *typep = (*typep)->tt_member;
 		else
@@ -3124,12 +3156,24 @@ compile_subscript(
 	    }
 	    else if (vtype == VAR_STRING)
 	    {
-		*typep = &t_number;
+		*typep = &t_string;
-		if (generate_instr_drop(cctx, ISN_STRINDEX, 1) == FAIL)
+		if ((is_slice
+			? generate_instr_drop(cctx, ISN_STRSLICE, 2)
+			: generate_instr_drop(cctx, ISN_STRINDEX, 1)) == FAIL)
+		    return FAIL;
+	    }
+	    else if (vtype == VAR_BLOB)
+	    {
+		emsg("Sorry, blob index and slice not implemented yet");
 		return FAIL;
 	    }
 	    else if (vtype == VAR_LIST || *typep == &t_any)
 	    {
+		if (is_slice)
+		{
+		    emsg("Sorry, list slice not implemented yet");
+		    return FAIL;
+		}
 		if ((*typep)->tt_type == VAR_LIST)
 		    *typep = (*typep)->tt_member;
 		if (generate_instr_drop(cctx, ISN_LISTINDEX, 1) == FAIL)
@@ -7052,6 +7096,7 @@ delete_instr(isn_T *isn)
 	case ISN_FOR:
 	case ISN_LISTINDEX:
 	case ISN_STRINDEX:
+	case ISN_STRSLICE:
 	case ISN_GETITEM:
 	case ISN_SLICE:
 	case ISN_MEMBER:

src/vim9execute.c

@@ -70,7 +70,7 @@ typedef struct {
 } ectx_T;
 
 // Get pointer to item relative to the bottom of the stack, -1 is the last one.
-#define STACK_TV_BOT(idx) (((typval_T *)ectx->ec_stack.ga_data) + ectx->ec_stack.ga_len + idx)
+#define STACK_TV_BOT(idx) (((typval_T *)ectx->ec_stack.ga_data) + ectx->ec_stack.ga_len + (idx))
 
     void
 to_string_error(vartype_T vartype)
@@ -2232,12 +2232,16 @@ call_def_function(
 		break;
 
 	    case ISN_STRINDEX:
+	    case ISN_STRSLICE:
 		{
-		    varnumber_T	n;
+		    int		is_slice = iptr->isn_type == ISN_STRSLICE;
+		    varnumber_T	n1 = 0, n2;
 		    char_u	*res;
 
 		    // string index: string is at stack-2, index at stack-1
-		    tv = STACK_TV_BOT(-2);
+		    // string slice: string is at stack-3, first index at
+		    // stack-2, second index at stack-1
+		    tv = is_slice ? STACK_TV_BOT(-3) : STACK_TV_BOT(-2);
 		    if (tv->v_type != VAR_STRING)
 		    {
 			SOURCING_LNUM = iptr->isn_lnum;
@@ -2245,6 +2249,18 @@ call_def_function(
 			goto on_error;
 		    }
 
+		    if (is_slice)
+		    {
+			tv = STACK_TV_BOT(-2);
+			if (tv->v_type != VAR_NUMBER)
+			{
+			    SOURCING_LNUM = iptr->isn_lnum;
+			    emsg(_(e_number_exp));
+			    goto on_error;
+			}
+			n1 = tv->vval.v_number;
+		    }
+
 		    tv = STACK_TV_BOT(-1);
 		    if (tv->v_type != VAR_NUMBER)
 		    {
@@ -2252,14 +2268,18 @@ call_def_function(
 			emsg(_(e_number_exp));
 			goto on_error;
 		    }
-		    n = tv->vval.v_number;
+		    n2 = tv->vval.v_number;
 
-		    // The resulting variable is a string of a single
+		    ectx.ec_stack.ga_len -= is_slice ? 2 : 1;
-		    // character.  If the index is too big or negative the
-		    // result is empty.
-		    --ectx.ec_stack.ga_len;
 		    tv = STACK_TV_BOT(-1);
-		    res = char_from_string(tv->vval.v_string, n);
+		    if (is_slice)
+			// Slice: Select the characters from the string
+			res = string_slice(tv->vval.v_string, n1, n2);
+		    else
+			// Index: The resulting variable is a string of a
+			// single character.  If the index is too big or
+			// negative the result is empty.
+			res = char_from_string(tv->vval.v_string, n2);
 		    vim_free(tv->vval.v_string);
 		    tv->vval.v_string = res;
 		}
@@ -3140,6 +3160,7 @@ ex_disassemble(exarg_T *eap)
 	    // expression operations
 	    case ISN_CONCAT: smsg("%4d CONCAT", current); break;
 	    case ISN_STRINDEX: smsg("%4d STRINDEX", current); break;
+	    case ISN_STRSLICE: smsg("%4d STRSLICE", current); break;
 	    case ISN_LISTINDEX: smsg("%4d LISTINDEX", current); break;
 	    case ISN_SLICE: smsg("%4d SLICE %lld",
 					 current, iptr->isn_arg.number); break;