add sort_by macro method

spec/compiler/macro/macro_methods_spec.cr

@@ -601,6 +601,10 @@ describe "macro methods" do
       assert_macro "", %({{["c".id, "b", "a".id].sort}}), [] of ASTNode, %([a, "b", c])
     end
 
+    it "executes sort_by" do
+      assert_macro "", %({{["abc", "a", "ab"].sort_by { |x| x.size }}}), [] of ASTNode, %(["a", "ab", "abc"])
+    end
+
     it "executes uniq" do
       assert_macro "", %({{[1, 1, 1, 2, 3, 1, 2, 3, 4].uniq}}), [] of ASTNode, %([1, 2, 3, 4])
     end

src/compiler/crystal/macros/methods.cr

@@ -1889,6 +1889,12 @@ private def intepret_array_or_tuple_method(object, klass, method, args, block, i
     klass.new(object.elements.shuffle)
   when "sort"
     klass.new(object.elements.sort { |x, y| x.interpret_compare(y) })
+  when "sort_by"
+    object.interpret_argless_method(method, args) do
+      raise "reject expects a block" unless block
+
+      sort_by(object, klass, block, interpreter)
+    end
   when "uniq"
     klass.new(object.elements.uniq)
   when "[]"
@@ -2005,3 +2011,16 @@ def filter(object, klass, block, interpreter, keep = true)
     keep ? block_result : !block_result
   })
 end
+
+private def sort_by(object, klass, block, interpreter)
+  block_arg = block.args.first?
+
+  klass.new(object.elements.sort { |x, y|
+    block_arg.try { |arg| interpreter.define_var(arg.name, x) }
+    x_result = interpreter.accept(block.body)
+    block_arg.try { |arg| interpreter.define_var(arg.name, y) }
+    y_result = interpreter.accept(block.body)
+
+    x_result.interpret_compare(y_result)
+  })
+end