Parser: comma is required between block args (#7343)

spec/compiler/parser/parser_spec.cr

@@ -571,6 +571,7 @@ module Crystal
     it_parses "foo { 1 }", Call.new(nil, "foo", block: Block.new(body: 1.int32))
     it_parses "foo { |a| 1 }", Call.new(nil, "foo", block: Block.new(["a".var], 1.int32))
     it_parses "foo { |a, b| 1 }", Call.new(nil, "foo", block: Block.new(["a".var, "b".var], 1.int32))
+    it_parses "foo { |a, b, | 1 }", Call.new(nil, "foo", block: Block.new(["a".var, "b".var], 1.int32))
     it_parses "1.foo do; 1; end", Call.new(1.int32, "foo", block: Block.new(body: 1.int32))
     it_parses "a b() {}", Call.new(nil, "a", Call.new(nil, "b", block: Block.new))
 
@@ -591,6 +592,16 @@ module Crystal
           "c".var,
         ] of ASTNode)))
 
+    it_parses "foo { |(_, c, )| c }", Call.new(nil, "foo",
+      block: Block.new(["__arg0".var],
+        Expressions.new([
+          Assign.new("c".var, Call.new("__arg0".var, "[]", 1.int32)),
+          "c".var,
+        ] of ASTNode)))
+
+    assert_syntax_error "foo { |a b| }", "expecting ',' or '|', not b"
+    assert_syntax_error "foo { |(a b)| }", "expecting ',' or ')', not b"
+
     it_parses "1 ? 2 : 3", If.new(1.int32, 2.int32, 3.int32)
     it_parses "1 ? a : b", If.new(1.int32, "a".call, "b".call)
     it_parses "1 ? a : b ? c : 3", If.new(1.int32, "a".call, If.new("b".call, "c".call, 3.int32))

src/compiler/crystal/syntax/parser.cr

@@ -4014,7 +4014,7 @@ module Crystal
       next_token_skip_space
       if @token.type == :"|"
         next_token_skip_space_or_newline
-        while @token.type != :"|"
+        while true
           if @token.type == :"*"
             if splat_index
               raise "splat block argument already specified", @token
@@ -4064,12 +4064,14 @@ module Crystal
               end
 
               next_token_skip_space_or_newline
-              if @token.type == :","
+              case @token.type
+              when :","
                 next_token_skip_space_or_newline
-              end
-
-              if @token.type == :")"
+                break if @token.type == :")"
+              when :")"
                 break
+              else
+                raise "expecting ',' or ')', not #{@token}", @token
               end
 
               i += 1
@@ -4084,8 +4086,15 @@ module Crystal
           block_args << var
 
           next_token_skip_space_or_newline
-          if @token.type == :","
+
+          case @token.type
+          when :","
             next_token_skip_space_or_newline
+            break if @token.type == :"|"
+          when :"|"
+            break
+          else
+            raise "expecting ',' or '|', not #{@token}", @token
           end
 
           arg_index += 1