Merge pull request #2681 from hurufu/remove-dcgs-that-have-failed-to-expand

Remove DCGs that have thrown an exception during term expansion

src/lib/dcgs.pl

@@ -214,10 +214,13 @@ dcg_cbody(( GRIf -> GRThen ), S0, S, ( If -> Then )) :-
     dcg_body(GRIf, S0, S1, If),
     dcg_body(GRThen, S1, S, Then).
 
+
+% When DCG expansion throws an exception – remove offending term and rethrow.
+user:term_expansion(throw_dcg_expansion_error(E), _) :-
+    throw(E).
 user:term_expansion(Term0, Term) :-
     nonvar(Term0),
-    dcg_rule(Term0, Term).
-
+    catch(dcg_rule(Term0, Term), E, Term = throw_dcg_expansion_error(E)).
 
 %% seq(Seq)//
 % 

tests/scryer/cli/issues/not_supported_dcg_constructs.in/main.pl

@@ -0,0 +1,6 @@
+:- use_module(library(dcgs)).
+
+d -->
+        (   { true } -> []
+        ;   { true } -> []
+        ).

tests/scryer/cli/issues/not_supported_dcg_constructs.stdout

@@ -0,0 +1 @@
+   error(representation_error(dcg_body),[culprit-({true}->[])]).

tests/scryer/cli/issues/not_supported_dcg_constructs.toml

@@ -0,0 +1,7 @@
+# issue 2675
+args = [
+    "-f",
+    "--no-add-history",
+    "-g", "halt",
+     "main.pl"
+]