edoc, syntax_tools: Don't fail on invalid UTF-8

As a temporary measure to ease the transition to default UTF-8
encoding, automatically fall back to the Latin-1 encoding (without any
warnings; the Erlang Compiler will emit a proper warning).

The intention is to remove this workaround in OTP 18 or 19.

2 files changed, 39 insertions, 2 deletions

diff --git a/lib/syntax_tools/src/epp_dodger.erl b/lib/syntax_tools/src/epp_dodger.erl
index 131be4e8e4..7e12eab1b5 100644
--- a/lib/syntax_tools/src/epp_dodger.erl
+++ b/lib/syntax_tools/src/epp_dodger.erl
@@ -184,9 +184,27 @@ quick_parse_file(File, Options) ->
     parse_file(File, fun quick_parse/3, Options ++ [no_fail]).
 
 parse_file(File, Parser, Options) ->
+    case do_parse_file(utf8, File, Parser, Options) of
+        {ok, Forms}=Ret ->
+            case find_invalid_unicode(Forms) of
+                none ->
+                    Ret;
+                invalid_unicode ->
+                    case epp:read_encoding(File) of
+                        utf8 ->
+                            Ret;
+                        _ ->
+                            do_parse_file(latin1, File, Parser, Options)
+                    end
+            end;
+        Else ->
+            Else
+    end.
+
+do_parse_file(DefEncoding, File, Parser, Options) ->
     case file:open(File, [read]) of
         {ok, Dev} ->
-            _ = epp:set_encoding(Dev),
+            _ = epp:set_encoding(Dev, DefEncoding),
             try Parser(Dev, 1, Options)
             after ok = file:close(Dev)
 	    end;
@@ -194,6 +212,14 @@ parse_file(File, Parser, Options) ->
             Error
     end.
 
+find_invalid_unicode([H|T]) ->
+    case H of
+	{error, {_Line, file_io_server, invalid_unicode}} ->
+	    invalid_unicode;
+	_Other ->
+	    find_invalid_unicode(T)
+    end;
+find_invalid_unicode([]) -> none.
 
 %% =====================================================================
 %% @spec parse(IODevice) -> {ok, Forms} | {error, errorinfo()}
diff --git a/lib/syntax_tools/src/erl_comment_scan.erl b/lib/syntax_tools/src/erl_comment_scan.erl
index dae7530ce7..03429d4d42 100644
--- a/lib/syntax_tools/src/erl_comment_scan.erl
+++ b/lib/syntax_tools/src/erl_comment_scan.erl
@@ -72,13 +72,24 @@ file(Name) ->
 	{ok, V} ->
 	    case V of
 		{ok, B} ->
-                    Enc = case epp:read_encoding(Name) of
+                    Encoding = epp:read_encoding_from_binary(B),
+                    Enc = case Encoding of
                               none -> epp:default_encoding();
                               Enc0 -> Enc0
                           end,
                     case catch unicode:characters_to_list(B, Enc) of
                         String when is_list(String) ->
                             string(String);
+                        R when Encoding =:= none ->
+                            case
+                              catch unicode:characters_to_list(B, latin1)
+                            of
+                                String when is_list(String) ->
+                                    string(String);
+                                _ ->
+                                    error_read_file(Name1),
+                                    exit(R)
+                            end;
                         R ->
                             error_read_file(Name1),
                             exit(R)