patch 8.2.2290: Vim9: unlet of global variable cannot be compiled

Problem:    Vim9: unlet of global variable cannot be compiled.
Solution:   Skip over variables that might be defined later. Give an error if
            a subscript is found. (closes #7585)

Author: brammool

src/eval.c

@@ -813,9 +813,9 @@ get_lval(
     // Clear everything in "lp".
     CLEAR_POINTER(lp);
 
-    if (skip)
+    if (skip || (flags & GLV_COMPILING))
     {
-	// When skipping just find the end of the name.
+	// When skipping or compiling just find the end of the name.
 	lp->ll_name = name;
 	lp->ll_name_end = find_name_end(name, NULL, NULL,
 						      FNE_INCL_BR | fne_flags);

src/testdir/test_vim9_assign.vim

@@ -1340,6 +1340,15 @@ def Test_unlet()
   assert_false(exists('s:somevar'))
   unlet! s:somevar
 
+  # can compile unlet before variable exists
+  # This doesn't work yet
+  #g:someDict = {key: 'val'}
+  #var k = 'key'
+  #unlet g:someDict[k]
+  #assert_equal({}, g:someDict)
+  #unlet g:someDict
+  #assert_false(exists('g:someDict'))
+
   CheckScriptFailure([
    'vim9script',
    'var svar = 123',

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    2290,
 /**/
     2289,
 /**/

src/vim.h

@@ -2544,12 +2544,14 @@ typedef enum {
 #define TFN_NO_DEREF	0x08	// do not dereference a Funcref
 #define TFN_READ_ONLY	0x10	// will not change the var
 #define TFN_NO_DECL	0x20	// only used for GLV_NO_DECL
+#define TFN_COMPILING	0x40	// only used for GLV_COMPILING
 
 // Values for get_lval() flags argument:
 #define GLV_QUIET	TFN_QUIET	// no error messages
 #define GLV_NO_AUTOLOAD	TFN_NO_AUTOLOAD	// do not use script autoloading
 #define GLV_READ_ONLY	TFN_READ_ONLY	// will not change the var
 #define GLV_NO_DECL	TFN_NO_DECL	// assignment without :var or :let
+#define GLV_COMPILING	TFN_COMPILING	// variable may be defined later
 
 #define DO_NOT_FREE_CNT 99999	// refcount for dict or list that should not
 				// be freed.

src/vim9compile.c

@@ -6130,6 +6130,12 @@ compile_unlet(
 
 	// Normal name.  Only supports g:, w:, t: and b: namespaces.
 	*name_end = NUL;
+	if (vim_strchr(p, '.') != NULL || vim_strchr(p, '[') != NULL)
+	{
+	    *name_end = cc;
+	    goto failed;
+	}
+
 	if (*p == '$')
 	    ret = generate_UNLET(cctx, ISN_UNLETENV, p + 1, eap->forceit);
 	else if (check_vim9_unlet(p) == FAIL)
@@ -6141,8 +6147,11 @@ compile_unlet(
 	return ret;
     }
 
+failed:
     // TODO: unlet {list}[idx]
     // TODO: unlet {dict}[key]
+    // complication: {list} can be global while "idx" is local, thus we can't
+    // call ex_unlet().
     emsg("Sorry, :unlet not fully implemented yet");
     return FAIL;
 }
@@ -6163,7 +6172,8 @@ compile_unletlock(char_u *arg, exarg_T *eap, cctx_T *cctx)
     }
 
     // TODO: this doesn't work for local variables
-    ex_unletlock(eap, p, 0, GLV_NO_AUTOLOAD, compile_unlet, cctx);
+    ex_unletlock(eap, p, 0, GLV_NO_AUTOLOAD | GLV_COMPILING,
+							  compile_unlet, cctx);
     return eap->nextcmd == NULL ? (char_u *)"" : eap->nextcmd;
 }