Make error messages clear blocks/keywords are disallowed in index assignment

Blocks and keywords are allowed in regular index.

Also update NEWS to make this more clear.

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

NEWS.md

@@ -19,9 +19,11 @@ Note that each entry is kept to a minimum, see links for details.
   `**nil` is treated similarly to `**{}`, passing no keywords,
   and not calling any conversion methods.  [[Bug #20064]]
 
-* Block passing is no longer allowed in index.  [[Bug #19918]]
+* Block passing is no longer allowed in index assignment
+  (e.g. `a[0, &b] = 1`).  [[Bug #19918]]
 
-* Keyword arguments are no longer allowed in index.  [[Bug #20218]]
+* Keyword arguments are no longer allowed in index assignment
+  (e.g. `a[0, kw: 1] = 2`).  [[Bug #20218]]
 
 ## Core classes updates
 

parse.y

@@ -13658,10 +13658,10 @@ aryset_check(struct parser_params *p, NODE *args)
         }
     }
     if (kwds && nd_type_p(kwds, NODE_HASH) && !RNODE_HASH(kwds)->nd_brace) {
-        yyerror1(&kwds->nd_loc, "keyword arg given in index");
+        yyerror1(&kwds->nd_loc, "keyword arg given in index assignment");
     }
     if (block) {
-        yyerror1(&block->nd_loc, "block arg given in index");
+        yyerror1(&block->nd_loc, "block arg given in index assignment");
     }
 }
 

prism/templates/src/diagnostic.c.erb

@@ -344,8 +344,8 @@ static const pm_diagnostic_data_t diagnostic_messages[PM_DIAGNOSTIC_ID_MAX] = {
     [PM_ERR_UNDEF_ARGUMENT]                     = { "invalid argument being passed to `undef`; expected a bare word, constant, or symbol argument", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNARY_RECEIVER]                     = { "unexpected %s, expected a receiver for unary `%c`", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_BLOCK_ARGUMENT]          = { "block argument should not be given", PM_ERROR_LEVEL_SYNTAX },
-    [PM_ERR_UNEXPECTED_INDEX_BLOCK]             = { "unexpected block arg given in index; blocks are not allowed in index expressions", PM_ERROR_LEVEL_SYNTAX },
-    [PM_ERR_UNEXPECTED_INDEX_KEYWORDS]          = { "unexpected keyword arg given in index; keywords are not allowed in index expressions", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_UNEXPECTED_INDEX_BLOCK]             = { "unexpected block arg given in index assignment; blocks are not allowed in index assignment expressions", PM_ERROR_LEVEL_SYNTAX },
+    [PM_ERR_UNEXPECTED_INDEX_KEYWORDS]          = { "unexpected keyword arg given in index assignment; keywords are not allowed in index assignment expressions", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_SAFE_NAVIGATION]         = { "&. inside multiple assignment destination", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_TOKEN_CLOSE_CONTEXT]     = { "unexpected %s, assuming it is closing the parent %s", PM_ERROR_LEVEL_SYNTAX },
     [PM_ERR_UNEXPECTED_TOKEN_IGNORE]            = { "unexpected %s, ignoring it", PM_ERROR_LEVEL_SYNTAX },

test/ruby/test_call.rb

@@ -136,7 +136,7 @@ class TestCall < Test::Unit::TestCase
     # Prevent "assigned but unused variable" warnings
     _ = [h, a, kw, b]
 
-    message = /keyword arg given in index/
+    message = /keyword arg given in index assignment/
 
     # +=, without block, non-popped
     assert_syntax_error(%q{h[**kw] += 1}, message)
@@ -270,7 +270,7 @@ class TestCall < Test::Unit::TestCase
     def o.[](...) 2 end
     def o.[]=(...) end
 
-    message = /keyword arg given in index/
+    message = /keyword arg given in index assignment/
 
     assert_syntax_error(%q{o[kw: 1] += 1}, message)
     assert_syntax_error(%q{o[**o] += 1}, message)
@@ -292,7 +292,7 @@ class TestCall < Test::Unit::TestCase
       def []=(*a, **b) @set = [a, b] end
     end.new
 
-    message = /keyword arg given in index/
+    message = /keyword arg given in index assignment/
 
     a = []
     kw = {}

test/ruby/test_parse.rb

@@ -512,12 +512,12 @@ class TestParse < Test::Unit::TestCase
     def t.dummy(_)
     end
 
-    assert_syntax_error("#{<<~"begin;"}\n#{<<~'end;'}", /block arg given in index/)
+    assert_syntax_error("#{<<~"begin;"}\n#{<<~'end;'}", /block arg given in index assignment/)
     begin;
       t[42, &blk] ||= 42
     end;
 
-    assert_syntax_error("#{<<~"begin;"}\n#{<<~'end;'}", /block arg given in index/)
+    assert_syntax_error("#{<<~"begin;"}\n#{<<~'end;'}", /block arg given in index assignment/)
     begin;
       t[42, &blk] ||= t.dummy 42 # command_asgn test
     end;