From dd9a4d6f559cac28fd74dac0ff62d27bfed66e64 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Valim?= <jose.valim@plataformatec.com.br>
Date: Fri, 17 May 2019 19:24:29 +0200
Subject: Always fallback to source when we can't parse AST

This commit fixes a bug in Dialyzer where it would assume
all Erlang AST can be converted back to valid Erlang code.
A case where this was is no true was already documented
in the source code, in relation to opaque types, but this
can also be true when it comes to other BEAM languages.
---
 lib/dialyzer/src/dialyzer.erl | 48 +++++++++++++++++++------------------------
 1 file changed, 21 insertions(+), 27 deletions(-)

diff --git a/lib/dialyzer/src/dialyzer.erl b/lib/dialyzer/src/dialyzer.erl
index d4fe064edd..c1bc5ff597 100644
--- a/lib/dialyzer/src/dialyzer.erl
+++ b/lib/dialyzer/src/dialyzer.erl
@@ -605,11 +605,9 @@ ordinal(N) when is_integer(N) -> io_lib:format("~wth", [N]).
 %% Functions that parse type strings, literal strings, and contract
 %% strings. Return strings formatted by erl_pp.
 
-%% If lib/hipe/cerl/erl_types.erl is compiled with DEBUG=true,
-%% the contents of opaque types are showed inside brackets.
-%% Since erl_parse:parse_form() cannot handle the bracket syntax,
-%% no indentation is done.
-%%-define(DEBUG , true).
+%% Note we always have to catch any error when trying to parse
+%% the syntax because other BEAM languages may not emit an
+%% Erlang AST that transforms into valid Erlang Source Code.
 
 -define(IND, 10).
 
@@ -620,13 +618,15 @@ con(M, F, Src, I) ->
 sig(Src, false) ->
   Src;
 sig(Src, true) ->
-  Str = lists:flatten(io_lib:format("-spec ~w:~tw~ts.", [a, b, Src])),
-  {ok, Tokens, _EndLocation} = erl_scan:string(Str),
-  exec(fun() ->
-           {ok, {attribute, _, spec, {_MFA, Types}}} =
-             erl_parse:parse_form(Tokens),
-           indentation(?IND) ++ pp_spec(Types)
-       end, Src).
+  try
+    Str = lists:flatten(io_lib:format("-spec ~w:~tw~ts.", [a, b, Src])),
+    {ok, Tokens, _EndLocation} = erl_scan:string(Str),
+    {ok, {attribute, _, spec, {_MFA, Types}}} =
+      erl_parse:parse_form(Tokens),
+    indentation(?IND) ++ pp_spec(Types)
+  catch
+    _:_ -> Src
+  end.
 
 %% Argument(list)s are a mix of types and Erlang code. Note: sometimes
 %% (contract_range, call_without_opaque, opaque_type_test), the initial
@@ -681,21 +681,15 @@ ts(Src) ->
   [C1|Src1] = Src, % $< (product) or $( (arglist)
   [C2|RevSrc2] = lists:reverse(Src1),
   Src2 = lists:reverse(RevSrc2),
-  exec(fun() ->
-           Types = parse_types_and_literals(Src2),
-           CommaInd = [$, | Ind],
-           (indentation(?IND-1) ++
-            [C1 | lists:join(CommaInd, [pp_type(Type) || Type <- Types])] ++
-            [C2])
-       end, Src).
-
--ifdef(DEBUG).
-exec(F, R) ->
-  try F() catch _:_ -> R end.
--else.
-exec(F, _) ->
-  F().
--endif.
+  try
+    Types = parse_types_and_literals(Src2),
+    CommaInd = [$, | Ind],
+    (indentation(?IND-1) ++
+     [C1 | lists:join(CommaInd, [pp_type(Type) || Type <- Types])] ++
+     [C2])
+  catch
+    _:_ -> Src
+  end.
 
 indentation(I) ->
   [$\n | lists:duplicate(I, $\s)].
-- 
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