Restrict qasm2 parser so it rejects multiple expressions in if body (#250)

Not sure if this is actually the intended solution, but at least it
works.

Funny enough, I had to adjust the `main.qasm` test file since it
included an invalid if statement. So we were actually testing that the
invalid syntax worked before.

Co-authored-by: Xiu-zhe (Roger) Luo <[email protected]>

Author: david-pl

src/bloqade/qasm2/parse/qasm2.lark

@@ -9,7 +9,7 @@ version: INT "." INT
 // stmts
 include: "include" STRING ";"
 ifstmt: "if" "(" expr "==" expr ")" ifbody
-ifbody: qop | "{" qop* "}" // allow multiple qops
+ifbody: qop
 opaque: "opaque" IDENTIFIER ["(" [params] ")"] qubits ";"
 barrier: "barrier" qubits ";"
 qreg: "qreg" IDENTIFIER "[" INT "]" ";"

test/qasm2/parse/invalid_programs/invalid_if.qasm

@@ -0,0 +1,9 @@
+OPENQASM 2.0;
+include "qelib1.inc";
+qreg q[1];
+creg c[1];
+
+if(c == 1) {
+    x q[0];
+    y q[0];
+}

test/qasm2/parse/programs/main.qasm

@@ -27,7 +27,3 @@ measure q -> c;
 measure q[1] -> c[1];
 
 if (c == 1) x q[0];
-if (c == 1) {
-    x q[0];
-    x q[0];
-}

test/qasm2/parse/programs/valid_if.qasm

@@ -0,0 +1,7 @@
+OPENQASM 2.0;
+include "qelib1.inc";
+qreg q[1];
+creg c[1];
+
+if(c == 1) x q[0];
+if(c == 1) y q[0];

test/qasm2/parse/test_roundtrip.py

@@ -1,30 +1,28 @@
 import os
 import pathlib
 
+import pytest
+from lark.exceptions import UnexpectedToken
+
 from bloqade.qasm2.parse import loads, spprint, loadfile
-from bloqade.qasm2.parse.parser import qasm2_parser as lark_parser
 
 
-def roundtrip(file):
-    ast1 = loadfile(os.path.join(os.path.dirname(__file__), "programs", file))
+def roundtrip(file, dirname):
+    ast1 = loadfile(os.path.join(os.path.dirname(__file__), dirname, file))
     ast2 = loads(spprint(ast1))
     return ast1 == ast2
 
 
 def test_roundtrip():
-    path = pathlib.Path(__file__).parent / "programs"
+    dirname = "programs"
+    path = pathlib.Path(__file__).parent / dirname
     for file in path.glob("*.qasm"):
-        assert roundtrip(file.name), f"Failed roundtrip for {file}"
-
+        assert roundtrip(file.name, dirname), f"Failed roundtrip for {file}"
 
-if __name__ == "__main__":
-    filepath = os.path.join(os.path.dirname(__file__), "programs", "global.qasm")
-    print(filepath)
-    with open(filepath) as f:
-        qasm_str = f.read()
 
-    parse_tree = lark_parser.parse(qasm_str)  # raw parsing seems to be fine
-    print(parse_tree.pretty())
-
-    ast = loads(qasm_str)
-    print(spprint(ast))
+def test_invalids():
+    dirname = "invalid_programs"
+    path = pathlib.Path(__file__).parent / dirname
+    for file in path.glob("*.qasm"):
+        with pytest.raises(UnexpectedToken):
+            roundtrip(file.name, dirname)