fix(eval): partially port v8.2.3284

These were issues that I found while porting that I fixed upstream. :^)

Very little of the patch can be exactly ported as we're a bit behind on
dependant patches (we also can't use the exact :for emsg, as we don't
support iterating over Strings yet), so just translate the fixes as best
as we can for now.

Include latest relevant doc changes from:
- v8.1.0815
- v8.2.2658

runtime/doc/eval.txt

@@ -372,8 +372,8 @@ Changing the order of items in a list: >
 
 For loop ~
 
-The |:for| loop executes commands for each item in a list.  A variable is set
-to each item in the list in sequence.  Example: >
+The |:for| loop executes commands for each item in a |List| or |Blob|.
+A variable is set to each item in the sequence.  Example with a List: >
 	:for item in mylist
 	:   call Doit(item)
 	:endfor
@@ -406,6 +406,8 @@ It is also possible to put remaining items in a List variable: >
 	:   endif
 	:endfor
 
+For a Blob one byte at a time is used.
+
 
 List functions ~
 						*E714*
@@ -637,6 +639,16 @@ is not available it returns -1 or the default value you specify: >
 	:echo get(myblob, idx, 999)
 
 
+Blob iteration ~
+
+The |:for| loop executes commands for each byte of a Blob.  The loop variable is
+set to each byte in the Blob.  Example: >
+	:for byte in 0z112233
+	:   call Doit(byte)
+	:endfor
+This calls Doit() with 0x11, 0x22 and 0x33.
+
+
 Blob concatenation ~
 
 Two blobs can be concatenated with the "+" operator: >
@@ -10999,28 +11011,34 @@ text...
 			NOTE: The ":append" and ":insert" commands don't work
 			properly inside a ":while" and ":for" loop.
 
-:for {var} in {list}					*:for* *E690* *E732*
+:for {var} in {object}					*:for* *E690* *E732*
 :endfo[r]						*:endfo* *:endfor*
 			Repeat the commands between ":for" and ":endfor" for
-			each item in {list}.  Variable {var} is set to the
-			value of each item.
-			When an error is detected for a command inside the
-			loop, execution continues after the "endfor".
-			Changing {list} inside the loop affects what items are
-			used.  Make a copy if this is unwanted: >
+			each item in {object}.  {object} can be a |List| or
+			a |Blob|.  Variable {var} is set to the value of each
+			item.  When an error is detected for a command inside
+			the loop, execution continues after the "endfor".
+			Changing {object} inside the loop affects what items
+			are used.  Make a copy if this is unwanted: >
 				:for item in copy(mylist)
-<			When not making a copy, Vim stores a reference to the
-			next item in the list, before executing the commands
-			with the current item.  Thus the current item can be
-			removed without effect.  Removing any later item means
-			it will not be found.  Thus the following example
-			works (an inefficient way to make a list empty): >
+<
+			When {object} is a |List| and not making a copy, Vim
+			stores a reference to the next item in the |List|
+			before executing the commands with the current item.
+			Thus the current item can be removed without effect.
+			Removing any later item means it will not be found.
+			Thus the following example works (an inefficient way
+			to make a |List| empty): >
 				for item in mylist
 				   call remove(mylist, 0)
 				endfor
-<			Note that reordering the list (e.g., with sort() or
+<			Note that reordering the |List| (e.g., with sort() or
 			reverse()) may have unexpected effects.
 
+			When {object} is a |Blob|, Vim always makes a copy to
+			iterate over.  Unlike with |List|, modifying the
+			|Blob| does not affect the iteration.
+
 :for [{var1}, {var2}, ...] in {listlist}
 :endfo[r]
 			Like ":for" above, but each item in {listlist} must be

src/nvim/eval.c

@@ -2614,7 +2614,7 @@ void *eval_for_line(const char_u *arg, bool *errp, char_u **nextcmdp, int skip)
         }
         tv_clear(&tv);
       } else {
-        EMSG(_(e_listreq));
+        EMSG(_(e_listblobreq));
         tv_clear(&tv);
       }
     }

src/nvim/eval/funcs.c

@@ -4984,12 +4984,16 @@ static void f_insert(typval_T *argvars, typval_T *rettv, FunPtr fptr)
   bool error = false;
 
   if (argvars[0].v_type == VAR_BLOB) {
-    if (argvars[0].vval.v_blob == NULL) {
+    blob_T *const b = argvars[0].vval.v_blob;
+
+    if (b == NULL
+        || var_check_lock(b->bv_lock, N_("insert() argument"),
+                          TV_TRANSLATE)) {
       return;
     }
 
     long before = 0;
-    const int len = tv_blob_len(argvars[0].vval.v_blob);
+    const int len = tv_blob_len(b);
 
     if (argvars[2].v_type != VAR_UNKNOWN) {
       before = (long)tv_get_number_chk(&argvars[2], &error);
@@ -5010,11 +5014,11 @@ static void f_insert(typval_T *argvars, typval_T *rettv, FunPtr fptr)
       return;
     }
 
-    ga_grow(&argvars[0].vval.v_blob->bv_ga, 1);
-    char_u *const p = (char_u *)argvars[0].vval.v_blob->bv_ga.ga_data;
+    ga_grow(&b->bv_ga, 1);
+    char_u *const p = (char_u *)b->bv_ga.ga_data;
     memmove(p + before + 1, p + before, (size_t)len - before);
     *(p + before) = val;
-    argvars[0].vval.v_blob->bv_ga.ga_len++;
+    b->bv_ga.ga_len++;
 
     tv_copy(&argvars[0], rettv);
   } else if (argvars[0].v_type != VAR_LIST) {
@@ -7312,11 +7316,16 @@ static void f_remove(typval_T *argvars, typval_T *rettv, FunPtr fptr)
       }
     }
   } else if (argvars[0].v_type == VAR_BLOB) {
+    blob_T *const b = argvars[0].vval.v_blob;
+
+    if (b != NULL && var_check_lock(b->bv_lock, arg_errmsg, TV_TRANSLATE)) {
+      return;
+    }
+
     bool error = false;
     idx = (long)tv_get_number_chk(&argvars[1], &error);
 
     if (!error) {
-      blob_T *const b = argvars[0].vval.v_blob;
       const int len = tv_blob_len(b);
 
       if (idx < 0) {

src/nvim/testdir/test_blob.vim

@@ -251,6 +251,12 @@ func Test_blob_func_remove()
   call assert_fails("call remove(1, 0)", 'E896:')
   call assert_fails("call remove(b, b)", 'E974:')
   call assert_fails("call remove(v:_null_blob, 1, 2)", 'E979:')
+
+  " Translated from v8.2.3284
+  let b = 0zDEADBEEF
+  lockvar b
+  call assert_fails('call remove(b, 0)', 'E741:')
+  unlockvar b
 endfunc
 
 func Test_blob_read_write()
@@ -308,6 +314,12 @@ func Test_blob_insert()
   call assert_fails('call insert(b, 257)', 'E475:')
   call assert_fails('call insert(b, 0, [9])', 'E745:')
   call assert_equal(0, insert(v:_null_blob, 0x33))
+
+  " Translated from v8.2.3284
+  let b = 0zDEADBEEF
+  lockvar b
+  call assert_fails('call insert(b, 3)', 'E741:')
+  unlockvar b
 endfunc
 
 func Test_blob_reverse()

src/nvim/testdir/test_eval_stuff.vim

@@ -23,9 +23,11 @@ func Test_E963()
 endfunc
 
 func Test_for_invalid()
-  call assert_fails("for x in 99", 'E714:')
-  call assert_fails("for x in function('winnr')", 'E714:')
-  call assert_fails("for x in {'a': 9}", 'E714:')
+  " Vim gives incorrect emsg here until v8.2.3284, but the exact emsg from that
+  " patch cannot be used until v8.2.2658 is ported (for loop over Strings)
+  call assert_fails("for x in 99", 'E897:')
+  call assert_fails("for x in function('winnr')", 'E897:')
+  call assert_fails("for x in {'a': 9}", 'E897:')
 
   if 0
     /1/5/2/s/\n