patch 8.1.1116: cannot enforce a Vim script style

Problem:    Cannot enforce a Vim script style.
Solution:   Add the :scriptversion command. (closes #3857)

runtime/doc/eval.txt

@@ -27,10 +27,11 @@ done, the features in this document are not available.  See |+eval| and
 7.  Commands			|expression-commands|
 8.  Exception handling		|exception-handling|
 9.  Examples			|eval-examples|
-10. No +eval feature		|no-eval-feature|
+10. Vim script version		|vimscript-version|
-11. The sandbox			|eval-sandbox|
+11. No +eval feature		|no-eval-feature|
-12. Textlock			|textlock|
+12. The sandbox			|eval-sandbox|
-13. Testing			|testing|
+13. Textlock			|textlock|
+14. Testing			|testing|
 
 {Vi does not have any of these commands}
 
@@ -1037,6 +1038,7 @@ result is a new list with the two lists Concatenated.
 
 For String concatenation ".." is preferred, since "." is ambiguous, it is also
 used for |Dict| member access and floating point numbers.
+When |vimscript-version| is 2 or higher, using "." is not allowed.
 
 expr7 * expr7  Number multiplication				*expr-star*
 expr7 / expr7  Number division					*expr-/*
@@ -10476,6 +10478,8 @@ vertsplit		Compiled with vertically split windows |:vsplit|.
 vim_starting		True while initial source'ing takes place. |startup|
 			*vim_starting*
 viminfo			Compiled with viminfo support.
+vimscript-1		Compiled Vim script version 1 support
+vimscript-2		Compiled Vim script version 2 support
 virtualedit		Compiled with 'virtualedit' option. (always true)
 visual			Compiled with Visual mode. (always true)
 visualextra		Compiled with extra Visual mode commands. (always
@@ -10966,16 +10970,19 @@ This does NOT work: >
 			When the selected range of items is partly past the
 			end of the list, items will be added.
 
-                                            *:let+=* *:let-=* *:letstar=*
+			*:let+=* *:let-=* *:letstar=*
-                                            *:let/=* *:let%=* *:let.=* *E734*
+			*:let/=* *:let%=* *:let.=* *:let..=* *E734* *E985*
 :let {var} += {expr1}	Like ":let {var} = {var} + {expr1}".
 :let {var} -= {expr1}	Like ":let {var} = {var} - {expr1}".
 :let {var} *= {expr1}	Like ":let {var} = {var} * {expr1}".
 :let {var} /= {expr1}	Like ":let {var} = {var} / {expr1}".
 :let {var} %= {expr1}	Like ":let {var} = {var} % {expr1}".
 :let {var} .= {expr1}	Like ":let {var} = {var} . {expr1}".
+:let {var} ..= {expr1}	Like ":let {var} = {var} .. {expr1}".
 			These fail if {var} was not set yet and when the type
 			of {var} and {expr1} don't fit the operator.
+			`.=` is not supported with Vim script version 2 and
+			later, see |vimscript-version|.
 
 
 :let ${env-name} = {expr1}			*:let-environment* *:let-$*
@@ -12609,7 +12616,34 @@ code can be used: >
     unlet scriptnames_output
 
 ==============================================================================
-10. No +eval feature				*no-eval-feature*
+10. Vim script versions		*vimscript-version* *vimscript-versions*
+
+Over time many features have been added to Vim script.  This includes Ex
+commands, functions, variable types, etc.  Each individual feature can be
+checked with the |has()| and |exists()| functions.
+
+Sometimes old syntax of functionality gets in the way of making Vim better.
+When support is taken away this will break older Vim scripts.  To make this
+explicit the |:scriptversion| command can be used.  When a Vim script is not
+compatible with older versions of Vim this will give an explicit error,
+instead of failing in mysterious ways. >
+
+ :scriptversion 1
+<	This is the original Vim script, same as not using a |:scriptversion|
+	command.  Can be used to go back to old syntax for a range of lines.
+	Test for support with: >
+		has('vimscript-1')
+
+ :scriptversion 2
+< 	String concatenation with "." is not supported, use ".." instead.
+	This avoids the ambiguity using "." for Dict member access and
+	floating point numbers.  Now ".5" means the number 0.5.
+	Test for support with: >
+		has('vimscript-2')
+
+
+==============================================================================
+11. No +eval feature				*no-eval-feature*
 
 When the |+eval| feature was disabled at compile time, none of the expression
 evaluation commands are available.  To prevent this from causing Vim scripts
@@ -12640,7 +12674,7 @@ When the |+eval| feature is available the command is skipped because of the
 silently ignored, and the command is executed.
 
 ==============================================================================
-11. The sandbox					*eval-sandbox* *sandbox* *E48*
+12. The sandbox					*eval-sandbox* *sandbox* *E48*
 
 The 'foldexpr', 'formatexpr', 'includeexpr', 'indentexpr', 'statusline' and
 'foldtext' options may be evaluated in a sandbox.  This means that you are
@@ -12679,7 +12713,7 @@ Note that when in the sandbox and saving an option value and restoring it, the
 option will still be marked as it was set in the sandbox.
 
 ==============================================================================
-12. Textlock							*textlock*
+13. Textlock							*textlock*
 
 In a few situations it is not allowed to change the text in the buffer, jump
 to another window and some other things that might confuse or break what Vim
@@ -12695,7 +12729,7 @@ This is not allowed when the textlock is active:
 	- etc.
 
 ==============================================================================
-13. Testing							*testing*
+14. Testing							*testing*
 
 Vim can be tested after building it, usually with "make test".
 The tests are located in the directory "src/testdir".

runtime/doc/repeat.txt

@@ -1,4 +1,4 @@
-*repeat.txt*    For Vim version 8.1.  Last change: 2018 Dec 18
+*repeat.txt*    For Vim version 8.1.  Last change: 2019 Apr 04
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -325,6 +325,17 @@ For writing a Vim script, see chapter 41 of the user manual |usr_41.txt|.
 <
 			{not in Vi}
 
+:scriptv[ersion] {version}		*:scriptv* *:scriptversion*
+								*E999* *E984*
+			Specify the version of Vim for the lines that follow.
+			Does not apply to sourced scripts.
+
+			If {version} is higher than what the current Vim
+			version supports E999 will be given.  You either need
+			to rewrite the script to make it work with an older
+			Vim version, or update Vim to a newer version.  See
+			|vimscript-version| for what changed between versions.
+
 						*:scr* *:scriptnames*
 :scr[iptnames]		List all sourced script names, in the order they were
 			first sourced.  The number is used for the script ID

src/buffer.c

@@ -5493,6 +5493,7 @@ chk_modeline(
 		current_sctx.sc_sid = SID_MODELINE;
 		current_sctx.sc_seq = 0;
 		current_sctx.sc_lnum = 0;
+		current_sctx.sc_version = 1;
 #endif
 		// Make sure no risky things are executed as a side effect.
 		secure = 1;

src/eval.c

@@ -1249,6 +1249,7 @@ ex_let(exarg_T *eap)
     char_u	op[2];
     char_u	*argend;
     int		first = TRUE;
+    int		concat;
 
     argend = skip_var_list(arg, &var_count, &semicolon);
     if (argend == NULL)
@@ -1256,14 +1257,19 @@ ex_let(exarg_T *eap)
     if (argend > arg && argend[-1] == '.')  // for var.='str'
 	--argend;
     expr = skipwhite(argend);
-    if (*expr != '=' && !((vim_strchr((char_u *)"+-*/%.", *expr) != NULL
+    concat = expr[0] == '.'
-			   && expr[1] == '=') || STRNCMP(expr, "..=", 3) == 0))
+	&& ((expr[1] == '=' && current_sctx.sc_version < 2)
+		|| (expr[1] == '.' && expr[2] == '='));
+    if (*expr != '=' && !((vim_strchr((char_u *)"+-*/%", *expr) != NULL
+						 && expr[1] == '=') || concat))
     {
 	/*
 	 * ":let" without "=": list variables
 	 */
 	if (*arg == '[')
 	    emsg(_(e_invarg));
+	else if (expr[0] == '.')
+	    emsg(_("E985: .= is not supported with script version 2"));
 	else if (!ends_excmd(*arg))
 	    /* ":let var1 var2" */
 	    arg = list_arg_vars(eap, arg, &first);
@@ -3817,7 +3823,7 @@ eval4(char_u **arg, typval_T *rettv, int evaluate)
  * Handle fourth level expression:
  *	+	number addition
  *	-	number subtraction
- *	.	string concatenation
+ *	.	string concatenation (if script version is 1)
  *	..	string concatenation
  *
  * "arg" must point to the first non-white of the expression.
@@ -3838,6 +3844,7 @@ eval5(char_u **arg, typval_T *rettv, int evaluate)
     char_u	*s1, *s2;
     char_u	buf1[NUMBUFLEN], buf2[NUMBUFLEN];
     char_u	*p;
+    int		concat;
 
     /*
      * Get the first variable.
@@ -3850,8 +3857,11 @@ eval5(char_u **arg, typval_T *rettv, int evaluate)
      */
     for (;;)
     {
+	// "." is only string concatenation when scriptversion is 1
 	op = **arg;
-	if (op != '+' && op != '-' && op != '.')
+	concat = op == '.'
+			&& (*(*arg + 1) == '.' || current_sctx.sc_version < 2);
+	if (op != '+' && op != '-' && !concat)
 	    break;
 
 	if ((op != '+' || (rettv->v_type != VAR_LIST
@@ -4224,6 +4234,17 @@ eval7(
 	*arg = skipwhite(*arg + 1);
     end_leader = *arg;
 
+    if (**arg == '.' && (!isdigit(*(*arg + 1))
+#ifdef FEAT_FLOAT
+	    || current_sctx.sc_version < 2
+#endif
+	    ))
+    {
+	semsg(_(e_invexpr2), *arg);
+	++*arg;
+	return FAIL;
+    }
+
     switch (**arg)
     {
     /*
@@ -4239,16 +4260,23 @@ eval7(
     case '7':
     case '8':
     case '9':
+    case '.':
 	{
 #ifdef FEAT_FLOAT
-		char_u *p = skipdigits(*arg + 1);
+		char_u *p;
 		int    get_float = FALSE;
 
 		/* We accept a float when the format matches
 		 * "[0-9]\+\.[0-9]\+\([eE][+-]\?[0-9]\+\)\?".  This is very
 		 * strict to avoid backwards compatibility problems.
+		 * With script version 2 and later the leading digit can be
+		 * omitted.
 		 * Don't look for a float after the "." operator, so that
 		 * ":let vers = 1.2.3" doesn't fail. */
+		if (**arg == '.')
+		    p = *arg;
+		else
+		    p = skipdigits(*arg + 1);
 		if (!want_string && p[0] == '.' && vim_isdigit(p[1]))
 		{
 		    get_float = TRUE;

src/evalfunc.c

@@ -6631,10 +6631,12 @@ f_has(typval_T *argvars, typval_T *rettv)
 #ifdef FEAT_VARTABS
 	"vartabs",
 #endif
+	"vertsplit",
 #ifdef FEAT_VIMINFO
 	"viminfo",
 #endif
-	"vertsplit",
+	"vimscript-1",
+	"vimscript-2",
 	"virtualedit",
 	"visual",
 	"visualextra",

src/ex_cmdidxs.h

@@ -24,13 +24,13 @@ static const unsigned short cmdidxs1[26] =
   /* q */ 348,
   /* r */ 351,
   /* s */ 371,
-  /* t */ 438,
+  /* t */ 439,
-  /* u */ 481,
+  /* u */ 482,
-  /* v */ 492,
+  /* v */ 493,
-  /* w */ 510,
+  /* w */ 511,
-  /* x */ 524,
+  /* x */ 525,
-  /* y */ 533,
+  /* y */ 534,
-  /* z */ 534
+  /* z */ 535
 };
 
 /*
@@ -59,7 +59,7 @@ static const unsigned char cmdidxs2[26][26] =
   /* p */ {  1,  0,  3,  0,  4,  0,  0,  0,  0,  0,  0,  0,  0,  0,  7,  9,  0,  0, 16, 17, 26,  0, 27,  0, 28,  0 },
   /* q */ {  2,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0 },
   /* r */ {  0,  0,  0,  0,  0,  0,  0,  0, 12,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 14, 19,  0,  0,  0,  0 },
-  /* s */ {  2,  6, 15,  0, 18, 22,  0, 24, 25,  0,  0, 28, 30, 34, 38, 40,  0, 48,  0, 49,  0, 61, 62,  0, 63,  0 },
+  /* s */ {  2,  6, 15,  0, 19, 23,  0, 25, 26,  0,  0, 29, 31, 35, 39, 41,  0, 49,  0, 50,  0, 62, 63,  0, 64,  0 },
   /* t */ {  2,  0, 19,  0, 22, 24,  0, 25,  0, 26,  0, 27, 31, 34, 36, 37,  0, 38, 40,  0, 41,  0,  0,  0,  0,  0 },
   /* u */ {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 10,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0 },
   /* v */ {  0,  0,  0,  0,  1,  0,  0,  0,  4,  0,  0,  0,  9, 12,  0,  0,  0,  0, 15,  0, 16,  0,  0,  0,  0,  0 },
@@ -69,4 +69,4 @@ static const unsigned char cmdidxs2[26][26] =
   /* z */ {  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0 }
 };
 
-static const int command_count = 547;
+static const int command_count = 548;

src/ex_cmds.h

@@ -1269,6 +1269,9 @@ EX(CMD_scriptnames,	"scriptnames",	ex_scriptnames,
 EX(CMD_scriptencoding,	"scriptencoding", ex_scriptencoding,
 			WORD1|TRLBAR|CMDWIN,
 			ADDR_LINES),
+EX(CMD_scriptversion,	"scriptversion", ex_scriptversion,
+			WORD1|TRLBAR|CMDWIN,
+			ADDR_LINES),
 EX(CMD_scscope,		"scscope",	ex_scscope,
 			EXTRA|NOTRLCOM,
 			ADDR_LINES),

src/ex_cmds2.c

@@ -2321,7 +2321,7 @@ check_changed_any(
 	    else
 #endif
 	    /* Try auto-writing the buffer.  If this fails but the buffer no
-	    * longer exists it's not changed, that's OK. */
+	     * longer exists it's not changed, that's OK. */
 	    if (check_changed(buf, (p_awa ? CCGD_AW : 0)
 				 | CCGD_MULTWIN
 				 | CCGD_ALLBUF) && bufref_valid(&bufref))
@@ -4501,12 +4501,14 @@ do_source(
      * Also starts profiling timer for nested script. */
     save_funccal(&funccalp_entry);
 
+    save_current_sctx = current_sctx;
+    current_sctx.sc_lnum = 0;
+    current_sctx.sc_version = 1;
+
     // Check if this script was sourced before to finds its SID.
     // If it's new, generate a new SID.
     // Always use a new sequence number.
-    save_current_sctx = current_sctx;
     current_sctx.sc_seq = ++last_current_SID_seq;
-    current_sctx.sc_lnum = 0;
 # ifdef UNIX
     stat_ok = (mch_stat((char *)fname_exp, &st) >= 0);
 # endif
@@ -5077,10 +5079,9 @@ script_line_end(void)
 
 /*
  * ":scriptencoding": Set encoding conversion for a sourced script.
- * Without the multi-byte feature it's simply ignored.
  */
     void
-ex_scriptencoding(exarg_T *eap UNUSED)
+ex_scriptencoding(exarg_T *eap)
 {
     struct source_cookie	*sp;
     char_u			*name;
@@ -5108,6 +5109,29 @@ ex_scriptencoding(exarg_T *eap UNUSED)
 	vim_free(name);
 }
 
+/*
+ * ":scriptversion": Set Vim script version for a sourced script.
+ */
+    void
+ex_scriptversion(exarg_T *eap UNUSED)
+{
+    int		nr;
+
+    if (!getline_equal(eap->getline, eap->cookie, getsourceline))
+    {
+	emsg(_("E984: :scriptversion used outside of a sourced file"));
+	return;
+    }
+
+    nr = getdigits(&eap->arg);
+    if (nr == 0 || *eap->arg != NUL)
+	emsg(_(e_invarg));
+    else if (nr > 2)
+	semsg(_("E999: scriptversion not supported: %d"), nr);
+    else
+	current_sctx.sc_version = nr;
+}
+
 #if defined(FEAT_EVAL) || defined(PROTO)
 /*
  * ":finish": Mark a sourced file as finished.

src/main.c

@@ -3166,6 +3166,7 @@ process_env(
 	current_sctx.sc_sid = SID_ENV;
 	current_sctx.sc_seq = 0;
 	current_sctx.sc_lnum = 0;
+	current_sctx.sc_version = 1;
 #endif
 	do_cmdline_cmd(initstr);
 	sourcing_name = save_sourcing_name;

src/option.c

@@ -407,7 +407,7 @@ struct vimoption
     char_u	*def_val[2];	// default values for variable (vi and vim)
 #ifdef FEAT_EVAL
     sctx_T	script_ctx;	// script context where the option was last set
-# define SCTX_INIT , {0, 0, 0}
+# define SCTX_INIT , {0, 0, 0, 1}
 #else
 # define SCTX_INIT
 #endif
@@ -5911,6 +5911,7 @@ set_string_option_direct(
 		script_ctx.sc_sid = set_sid;
 		script_ctx.sc_seq = 0;
 		script_ctx.sc_lnum = 0;
+		script_ctx.sc_version = 1;
 	    }
 	    set_option_sctx_idx(idx, opt_flags, script_ctx);
 	}

src/proto/ex_cmds2.pro

@@ -98,6 +98,7 @@ void script_line_start(void);
 void script_line_exec(void);
 void script_line_end(void);
 void ex_scriptencoding(exarg_T *eap);
+void ex_scriptversion(exarg_T *eap);
 void ex_finish(exarg_T *eap);
 void do_finish(exarg_T *eap, int reanimate);
 int source_finished(char_u *(*fgetline)(int, void *, int), void *cookie);

src/structs.h

@@ -79,6 +79,7 @@ typedef struct {
     scid_T	sc_sid;		// script ID
     int		sc_seq;		// sourcing sequence number
     linenr_T	sc_lnum;	// line number
+    int		sc_version;	// :scriptversion
 } sctx_T;
 
 /*

src/testdir/test_eval_stuff.vim

@@ -123,3 +123,39 @@ func Test_string_concatenation()
   let a..=b
   call assert_equal('ab', a)
 endfunc
+
+scriptversion 2
+func Test_string_concat_scriptversion2()
+  let a = 'a'
+  let b = 'b'
+
+  call assert_fails('echo a . b', 'E15:')
+  call assert_fails('let a .= b', 'E985:')
+  call assert_fails('let vers = 1.2.3', 'E15:')
+
+  if has('float')
+    let f = .5
+    call assert_equal(0.5, f)
+  endif
+endfunc
+
+scriptversion 1
+func Test_string_concat_scriptversion1()
+  let a = 'a'
+  let b = 'b'
+
+  echo a . b
+  let a .= b
+  let vers = 1.2.3
+  call assert_equal('123', vers)
+
+  if has('float')
+    call assert_fails('let f = .5', 'E15:')
+  endif
+endfunc
+
+func Test_scriptversion()
+  call writefile(['scriptversion 9'], 'Xversionscript')
+  call assert_fails('source Xversionscript', 'E999:')
+  call delete('Xversionscript')
+endfunc

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1116,
 /**/
     1115,
 /**/