Remove DCGs that have thrown an exception during term expansion

Some DCG constructs aren't supported and can't be expanded, here we
remove offending DCG rule and don't compile it at all – in a similar
fashion to what we do when incorrect goal was found – whole predicate
isn't getting compiled.

Fixes #2675

diff --git a/src/lib/dcgs.pl b/src/lib/dcgs.pl
index 200e57a8e8205ca98c2bc14673f21bc79e9711f0..2dc858a46e9cc152015bcc7153a7b42334f18a8c 100644 (file)
--- a/src/lib/dcgs.pl
+++ b/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)//
 % 

diff --git a/tests/scryer/cli/issues/not_supported_dcg_constructs.in/main.pl b/tests/scryer/cli/issues/not_supported_dcg_constructs.in/main.pl
new file mode 100644 (file)
index 0000000..188e02a
--- /dev/null
+++ b/tests/scryer/cli/issues/not_supported_dcg_constructs.in/main.pl
@@ -0,0 +1,6 @@
+:- use_module(library(dcgs)).
+
+d -->
+        (   { true } -> []
+        ;   { true } -> []
+        ).

diff --git a/tests/scryer/cli/issues/not_supported_dcg_constructs.stderr b/tests/scryer/cli/issues/not_supported_dcg_constructs.stderr
new file mode 100644 (file)
index 0000000..e69de29

diff --git a/tests/scryer/cli/issues/not_supported_dcg_constructs.stdout b/tests/scryer/cli/issues/not_supported_dcg_constructs.stdout
new file mode 100644 (file)
index 0000000..664e0e2
--- /dev/null
+++ b/tests/scryer/cli/issues/not_supported_dcg_constructs.stdout
@@ -0,0 +1 @@
+   error(representation_error(dcg_body),[culprit-({true}->[])]).

diff --git a/tests/scryer/cli/issues/not_supported_dcg_constructs.toml b/tests/scryer/cli/issues/not_supported_dcg_constructs.toml
new file mode 100644 (file)
index 0000000..12c5176
--- /dev/null
+++ b/tests/scryer/cli/issues/not_supported_dcg_constructs.toml
@@ -0,0 +1,7 @@
+# issue 2675
+args = [
+    "-f",
+    "--no-add-history",
+    "-g", "halt",
+     "main.pl"
+]