ast/parser: Remove early MHS return in infix parsing. (open-policy-ag…

…ent#4773)

This parser change allows the parser to properly fall through to the RHS
case where it was not doing so before, due to returning early during MHS
parsing in the parseTermIn() function.

Fixes open-policy-agent#4672.

Signed-off-by: Philip Conrad <philipaconrad@gmail.com>

ast/parser.go

@@ -1106,7 +1106,6 @@ func (p *Parser) parseTermIn(lhs *Term, keyVal bool, offset int) *Term {
 				}
 			}
 			p.restore(s)
-			return nil
 		}
 		if op := p.parseTermOpName(Member.Ref(), tokens.In); op != nil {
 			if rhs := p.parseTermRelation(nil, p.s.loc.Offset); rhs != nil {

ast/parser_test.go

@@ -2400,6 +2400,97 @@ func TestNoMatchError(t *testing.T) {
 	}
 }
 
+func TestBraceBracketParenMatchingErrors(t *testing.T) {
+	// Checks to prevent regression on issue #4672.
+	// Error location is important here, which is why we check
+	// the error strings directly.
+	tests := []struct {
+		note  string
+		err   string
+		input string
+	}{
+		{
+			note: "Unmatched ')' case",
+			err: `1 error occurred: test.rego:4: rego_parse_error: unexpected , token: expected \n or ; or }
+	y := contains("a"), "b")
+	                  ^`,
+			input: `package test
+p {
+	x := 5
+	y := contains("a"), "b")
+}`,
+		},
+		{
+			note: "Unmatched '}' case",
+			err: `1 error occurred: test.rego:4: rego_parse_error: unexpected , token: expected \n or ; or }
+	y := {"a", "b", "c"}, "a"}
+	                    ^`,
+			input: `package test
+p {
+	x := 5
+	y := {"a", "b", "c"}, "a"}
+}`,
+		},
+		{
+			note: "Unmatched ']' case",
+			err: `1 error occurred: test.rego:4: rego_parse_error: unexpected , token: expected \n or ; or }
+	y := ["a", "b", "c"], "a"]
+	                    ^`,
+			input: `package test
+p {
+	x := 5
+	y := ["a", "b", "c"], "a"]
+}`,
+		},
+		{
+			note: "Unmatched '(' case",
+			err: `1 error occurred: test.rego:5: rego_parse_error: unexpected } token: expected "," or ")"
+	}
+	^`,
+			input: `package test
+p {
+	x := 5
+	y := contains("a", "b"
+}`,
+		},
+		{
+			note: "Unmatched '{' case",
+
+			err: `1 error occurred: test.rego:5: rego_parse_error: unexpected eof token: expected \n or ; or }
+	}
+	^`,
+			input: `package test
+p {
+	x := 5
+	y := {{"a", "b", "c"}, "a"
+}`,
+		},
+		{
+			note: "Unmatched '[' case",
+			err: `1 error occurred: test.rego:5: rego_parse_error: unexpected } token: expected "," or "]"
+	}
+	^`,
+			input: `package test
+p {
+	x := 5
+	y := [["a", "b", "c"], "a"
+}`,
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.note, func(t *testing.T) {
+			_, err := ParseModule("test.rego", tc.input)
+			if err == nil {
+				t.Fatal("Expected error")
+			}
+			if tc.err != "" && tc.err != err.Error() {
+				t.Fatalf("Expected error string %q but got: %q", tc.err, err.Error())
+			}
+		})
+	}
+}
+
 func TestParseErrorDetails(t *testing.T) {
 
 	tests := []struct {