Allow multiple parameters and blocks for operators ending in =

spec/compiler/parser/parser_spec.cr

@@ -290,10 +290,16 @@ module Crystal
     assert_syntax_error "def foo=(*args); end", "setter method 'foo=' cannot have more than one parameter"
     assert_syntax_error "def foo=(**kwargs); end", "setter method 'foo=' cannot have more than one parameter"
     assert_syntax_error "def foo=(&block); end", "setter method 'foo=' cannot have a block"
-    assert_syntax_error "def []=(&block); end", "setter method '[]=' cannot have a block"
     assert_syntax_error "f.[]= do |a| end", "setter method '[]=' cannot be called with a block"
     assert_syntax_error "f.[]= { |bar| }", "setter method '[]=' cannot be called with a block"
 
+    # #10397
+    %w(<= >= == != []= ===).each do |operator|
+      it_parses "def #{operator}(other, file = 1); end", Def.new(operator, ["other".arg, Arg.new("file", 1.int32)])
+      it_parses "def #{operator}(*args, **opts); end", Def.new(operator, ["args".arg], splat_index: 0, double_splat: "opts".arg)
+      it_parses "def #{operator}(*args, **opts, &); end", Def.new(operator, ["args".arg], splat_index: 0, double_splat: "opts".arg, block_arg: Arg.new(""), block_arity: 0)
+    end
+
     # #5895, #6042, #5997
     %w(
       begin nil true false yield with abstract

src/compiler/crystal/syntax/parser.cr

@@ -3658,8 +3658,8 @@ module Crystal
 
         end_location = token_end_location
 
-        if name.ends_with?('=')
-          if name != "[]=" && (params.size > 1 || found_splat || found_double_splat)
+        if Lexer.setter?(name)
+          if params.size > 1 || found_splat || found_double_splat
             raise "setter method '#{name}' cannot have more than one parameter"
           elsif found_block
             raise "setter method '#{name}' cannot have a block"