Disallow '!' or '?' at the end of the LHS in an assignment

Issue: #6685
This affects mainly variable defined in top level, instance and class variable raise already an exception.

spec/compiler/parser/parser_spec.cr

@@ -152,6 +152,8 @@ module Crystal
     it_parses "@a, b = 1, 2", MultiAssign.new(["@a".instance_var, "b".var] of ASTNode, [1.int32, 2.int32] of ASTNode)
     it_parses "@@a, b = 1, 2", MultiAssign.new(["@@a".class_var, "b".var] of ASTNode, [1.int32, 2.int32] of ASTNode)
 
+    assert_syntax_error "b? = 1", "unexpected token: ="
+    assert_syntax_error "b! = 1", "unexpected token: ="
     assert_syntax_error "a, B = 1, 2", "can't assign to constant in multiple assignment"
 
     assert_syntax_error "1 == 2, a = 4"

src/compiler/crystal/command.cr

@@ -198,7 +198,7 @@ class Crystal::Command
   end
 
   private def execute(output_filename, run_args, compiler)
-    time? = @time && !@progress_tracker.stats?
+    time = @time && !@progress_tracker.stats?
     status, elapsed_time = @progress_tracker.stage("Execute") do
       begin
         elapsed = Time.measure do
@@ -221,7 +221,7 @@ class Crystal::Command
       end
     end
 
-    if time?
+    if time
       puts "Execute: #{elapsed_time}"
     end
 

src/compiler/crystal/syntax/parser.cr

@@ -315,7 +315,6 @@ module Crystal
           break
         when :"="
           slash_is_regex!
-
           if atomic.is_a?(Call) && atomic.name == "[]"
             next_token_skip_space_or_newline
 
@@ -333,6 +332,11 @@ module Crystal
               raise "can't change the value of self", location
             end
 
+            if atomic.is_a?(Call) && (atomic.name.ends_with?('?') ||
+               atomic.name.ends_with?('!'))
+              raise "unexpected token: =", location
+            end
+
             atomic = Var.new(atomic.name).at(atomic) if atomic.is_a?(Call)
 
             next_token_skip_space_or_newline