patch 8.2.0960: cannot use :import in legacy Vim script

Problem:    Cannot use :import in legacy Vim script.
Solution:   Support :import in any Vim script.

src/evalvars.c

@@ -2359,9 +2359,13 @@ get_var_tv(
 	    *dip = v;
     }
 
-    if (tv == NULL && current_sctx.sc_version == SCRIPT_VERSION_VIM9)
+    if (tv == NULL && (current_sctx.sc_version == SCRIPT_VERSION_VIM9
+					       || STRNCMP(name, "s:", 2) == 0))
     {
-	imported_T *import = find_imported(name, 0, NULL);
+	imported_T  *import;
+	char_u	    *p = STRNCMP(name, "s:", 2) == 0 ? name + 2 : name;
+
+	import = find_imported(p, 0, NULL);
 
 	// imported variable from another script
 	if (import != NULL)

src/testdir/test_vim9_script.vim

@@ -736,7 +736,7 @@ def Test_vim9script_fails()
   CheckScriptFailure(['scriptversion 2', 'vim9script'], 'E1039:')
   CheckScriptFailure(['vim9script', 'scriptversion 2'], 'E1040:')
   CheckScriptFailure(['export let some = 123'], 'E1042:')
-  CheckScriptFailure(['import some from "./Xexport.vim"'], 'E1042:')
+  CheckScriptFailure(['import some from "./Xexport.vim"'], 'E1048:')
   CheckScriptFailure(['vim9script', 'export let g:some'], 'E1044:')
   CheckScriptFailure(['vim9script', 'export echo 134'], 'E1043:')
 
@@ -1836,6 +1836,47 @@ def Test_forward_declaration()
   delete('Xforward')
 enddef
 
+def Test_source_vim9_from_legacy()
+  let legacy_lines =<< trim END
+    source Xvim9_script.vim
+
+    call assert_false(exists('local'))
+    call assert_false(exists('exported'))
+    call assert_false(exists('s:exported'))
+    call assert_equal('global', global)
+    call assert_equal('global', g:global)
+
+    " imported variable becomes script-local
+    import exported from './Xvim9_script.vim'
+    call assert_equal('exported', s:exported)
+    call assert_false(exists('exported'))
+
+    " imported function becomes script-local
+    import GetText from './Xvim9_script.vim'
+    call assert_equal('text', s:GetText())
+    call assert_false(exists('*GetText'))
+  END
+  writefile(legacy_lines, 'Xlegacy_script.vim')
+
+  let vim9_lines =<< trim END
+    vim9script
+    let local = 'local'
+    g:global = 'global'
+    export let exported = 'exported'
+    export def GetText(): string
+       return 'text'
+    enddef
+  END
+  writefile(vim9_lines, 'Xvim9_script.vim')
+
+  source Xlegacy_script.vim
+
+  assert_equal('global', g:global)
+"  unlet g:global
+
+  delete('Xlegacy_script.vim')
+  delete('Xvim9_script.vim')
+enddef
 
 " Keep this last, it messes up highlighting.
 def Test_substitute_cmd()

src/userfunc.c

@@ -719,15 +719,39 @@ find_func_even_dead(char_u *name, int is_global, cctx_T *cctx)
     ufunc_T	*func;
     imported_T	*imported;
 
-    if (in_vim9script() && !is_global)
+    if (!is_global)
+    {
+	char_u *after_script = NULL;
+
+	if (in_vim9script())
 	{
 	    // Find script-local function before global one.
 	    func = find_func_with_sid(name, current_sctx.sc_sid);
 	    if (func != NULL)
 		return func;
+	}
 
-	// Find imported funcion before global one.
+	if (!in_vim9script()
-	imported = find_imported(name, 0, cctx);
+		&& name[0] == K_SPECIAL
+		&& name[1] == KS_EXTRA
+		&& name[2] == KE_SNR)
+	{
+	    long sid;
+
+	    // Caller changes s: to <SNR>99_name.
+
+	    after_script = name + 3;
+	    sid = getdigits(&after_script);
+	    if (sid == current_sctx.sc_sid && *after_script == '_')
+		++after_script;
+	    else
+		after_script = NULL;
+	}
+	if (in_vim9script() || after_script != NULL)
+	{
+	    // Find imported function before global one.
+	    imported = find_imported(
+			  after_script == NULL ? name : after_script, 0, cctx);
 	    if (imported != NULL && imported->imp_funcname != NULL)
 	    {
 		hi = hash_find(&func_hashtab, imported->imp_funcname);
@@ -735,6 +759,7 @@ find_func_even_dead(char_u *name, int is_global, cctx_T *cctx)
 		    return HI2UF(hi);
 	    }
 	}
+    }
 
     hi = hash_find(&func_hashtab,
 				STRNCMP(name, "g:", 2) == 0 ? name + 2 : name);

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    960,
 /**/
     959,
 /**/

src/vim9script.c

@@ -17,7 +17,7 @@
 
 #include "vim9.h"
 
-static char e_needs_vim9[] = N_("E1042: import/export can only be used in vim9script");
+static char e_needs_vim9[] = N_("E1042: export can only be used in vim9script");
 
     int
 in_vim9script(void)
@@ -141,17 +141,11 @@ free_imports(int sid)
     void
 ex_import(exarg_T *eap)
 {
-    if (current_sctx.sc_version != SCRIPT_VERSION_VIM9)
+    char_u *cmd_end = handle_import(eap->arg, NULL, current_sctx.sc_sid, NULL);
-	emsg(_(e_needs_vim9));
-    else
-    {
-	char_u *cmd_end = handle_import(eap->arg, NULL,
-						    current_sctx.sc_sid, NULL);
 
     if (cmd_end != NULL)
 	eap->nextcmd = check_nextcmd(cmd_end);
 }
-}
 
 /*
  * Find an exported item in "sid" matching the name at "*argp".