vim-patch:8.2.1479: Vim9: error for list index uses wrong line number

Problem:    Vim9: error for list index uses wrong line number.
Solution:   Set source line number. (closes vim/vim#6724)  Add a way to assert the
            line number of the error with assert_fails().

1d634542cf

Co-authored-by: Bram Moolenaar <Bram@vim.org>

runtime/doc/testing.txt

@@ -98,8 +98,9 @@ assert_exception({error} [, {msg}])			*assert_exception()*
 			catch
 			  call assert_exception('E492:')
 			endtry
-
-assert_fails({cmd} [, {error} [, {msg}]])			*assert_fails()*
+<
+							*assert_fails()*
+assert_fails({cmd} [, {error} [, {msg} [, {lnum}]]])
 		Run {cmd} and add an error message to |v:errors| if it does
 		NOT produce an error or when {error} is not found in the
 		error message.  Also see |assert-return|.
@@ -118,13 +119,21 @@ assert_fails({cmd} [, {error} [, {msg}]])			*assert_fails()*
 		string for the first error: >
 			assert_fails('cmd', ['', 'E987:'])
 <
+		If {msg} is empty then it is not used.  Do this to get the
+		default message when passing the {lnum} argument.
+
+		When {lnum} is present and not negative, and the {error}
+		argument is present and matches, then this is compared with
+		the line number at which the error was reported. That can be
+		the line number in a function or in a script.
+
 		Note that beeping is not considered an error, and some failing
 		commands only beep.  Use |assert_beeps()| for those.
 
 		Can also be used as a |method|: >
 			GetCmd()->assert_fails('E99:')
 
-assert_false({actual} [, {msg}])				*assert_false()*
+assert_false({actual} [, {msg}])			*assert_false()*
 		When {actual} is not false an error message is added to
 		|v:errors|, like with |assert_equal()|.
 		Also see |assert-return|.

src/nvim/eval.lua

@@ -38,7 +38,7 @@ return {
     assert_equal={args={2, 3}, base=2},
     assert_equalfile={args={2, 3}, base=1},
     assert_exception={args={1, 2}},
-    assert_fails={args={1, 3}, base=1},
+    assert_fails={args={1, 4}, base=1},
     assert_false={args={1, 2}, base=1},
     assert_inrange={args={3, 4}, base=3},
     assert_match={args={2, 3}, base=2},

src/nvim/globals.h

@@ -197,6 +197,7 @@ EXTERN bool emsg_severe INIT(= false);      // use message of next of several
 // used by assert_fails()
 EXTERN bool emsg_assert_fails_used INIT(= false);
 EXTERN char *emsg_assert_fails_msg INIT(= NULL);
+EXTERN long emsg_assert_fails_lnum INIT(= 0);
 
 EXTERN bool did_endif INIT(= false);        // just had ":endif"
 EXTERN dict_T vimvardict;                   // Dictionary with v: variables

src/nvim/message.c

@@ -665,6 +665,7 @@ static bool emsg_multiline(const char *s, bool multiline)
 
     if (emsg_assert_fails_used && emsg_assert_fails_msg == NULL) {
       emsg_assert_fails_msg = xstrdup(s);
+      emsg_assert_fails_lnum = SOURCING_LNUM;
     }
 
     // set "v:errmsg", also when using ":silent! cmd"

src/nvim/testing.c

@@ -124,7 +124,10 @@ static void fill_assert_error(garray_T *gap, typval_T *opt_msg_tv, char_u *exp_s
   bool did_copy = false;
   int omitted = 0;
 
-  if (opt_msg_tv->v_type != VAR_UNKNOWN) {
+  if (opt_msg_tv->v_type != VAR_UNKNOWN
+      && !(opt_msg_tv->v_type == VAR_STRING
+           && (opt_msg_tv->vval.v_string == NULL
+               || *opt_msg_tv->vval.v_string == NUL))) {
     tofree = (char_u *)encode_tv2echo(opt_msg_tv, NULL);
     ga_concat(gap, (char *)tofree);
     xfree(tofree);
@@ -497,6 +500,7 @@ void f_assert_fails(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     char buf[NUMBUFLEN];
     const char *expected;
     bool error_found = false;
+    bool lnum_error_found = false;
     char *actual = emsg_assert_fails_msg == NULL ? "[unknown]" : emsg_assert_fails_msg;
 
     if (argvars[1].v_type == VAR_STRING) {
@@ -525,12 +529,25 @@ void f_assert_fails(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
       goto theend;
     }
 
+    if (!error_found && argvars[3].v_type == VAR_NUMBER
+        && argvars[3].vval.v_number >= 0
+        && argvars[3].vval.v_number != emsg_assert_fails_lnum) {
+      error_found = true;
+      lnum_error_found = true;
+    }
+
     if (error_found) {
       typval_T actual_tv;
-      actual_tv.v_type = VAR_STRING;
-      actual_tv.vval.v_string = actual;
       prepare_assert_error(&ga);
-      fill_assert_error(&ga, &argvars[2], NULL, &argvars[1],
+      if (lnum_error_found) {
+        actual_tv.v_type = VAR_NUMBER;
+        actual_tv.vval.v_number = emsg_assert_fails_lnum;
+      } else {
+        actual_tv.v_type = VAR_STRING;
+        actual_tv.vval.v_string = actual;
+      }
+      fill_assert_error(&ga, &argvars[2], NULL,
+                        &argvars[lnum_error_found ? 3 : 1],
                         &actual_tv, ASSERT_OTHER);
       ga_concat(&ga, ": ");
       assert_append_cmd_or_arg(&ga, argvars, cmd);