Merge branch 'gomoripeti/syntax_tools/merl-transform/PR-1123/OTP-13755' into maint

* gomoripeti/syntax_tools/merl-transform/PR-1123/OTP-13755:
  Fix infinite loop in merl_transform

2 files changed, 24 insertions, 4 deletions

diff --git a/lib/syntax_tools/src/merl_tests.erl b/lib/syntax_tools/src/merl_tests.erl
index c1aae3100e..27db594050 100644
--- a/lib/syntax_tools/src/merl_tests.erl
+++ b/lib/syntax_tools/src/merl_tests.erl
@@ -48,6 +48,21 @@ parse_error_test_() ->
                    f(merl:quote("{")))
     ].
 
+transform_parse_error_test_() ->
+    [?_assertEqual("merl:quote(\"{\")",
+                   f(merl_transform:parse_transform(
+                       [?Q("merl:quote(\"{\")")], []))),
+     ?_assertEqual("merl:quote(2, \"{\")",
+                   f(merl_transform:parse_transform(
+                       [?Q("merl:quote(2, \"{\")")], []))),
+     ?_assertEqual("merl:qquote(\"{\", [{var, V}])",
+                   f(merl_transform:parse_transform(
+                       [?Q("merl:qquote(\"{\", [{var, V}])")], []))),
+     ?_assertEqual("merl:qquote(2, \"{\", [{var, V}])",
+                   f(merl_transform:parse_transform(
+                       [?Q("merl:qquote(2, \"{\", [{var, V}])")], [])))
+    ].
+
 term_test_() ->
     [?_assertEqual(tuple, erl_syntax:type(merl:term({}))),
      ?_assertEqual("{foo, 42}", f(merl:term({foo, 42})))
diff --git a/lib/syntax_tools/src/merl_transform.erl b/lib/syntax_tools/src/merl_transform.erl
index fe58b6a122..497baddd0a 100644
--- a/lib/syntax_tools/src/merl_transform.erl
+++ b/lib/syntax_tools/src/merl_transform.erl
@@ -104,10 +104,15 @@ expand_qquote([Text, Env], T, Line) ->
     case erl_syntax:is_literal(Text) of
         true ->
             As = [Line, erl_syntax:concrete(Text)],
-            %% expand further if possible
-            expand(merl:qquote(Line, "merl:subst(_@tree, _@env)",
-                               [{tree, eval_call(Line, quote, As, T)},
-                                {env, Env}]));
+            case eval_call(Line, quote, As, failed) of
+                failed ->
+                    T;
+                T1 ->
+                    %% expand further if possible
+                    expand(merl:qquote(Line, "merl:subst(_@tree, _@env)",
+                                       [{tree, T1},
+                                        {env, Env}]))
+            end;
         false ->
             T
     end;