Python API: fix bindings when assertions are disabled

Python's -O command-line option disableds the execution of "assert"
statements. In order for the generated Python bindings to work in such a
mode, we need to keep assertion logic only in "assert" statements. This
commit fixes statements that currently don't respect this principle.

Fixes GitHub issue AdaCore#485
TN: U326-020

langkit/templates/python_api/module_py.mako

@@ -707,7 +707,8 @@ class AnalysisUnit(object):
         result = []
         diag = Diagnostic._c_type()
         for i in range(count):
-            assert _unit_diagnostic(self._c_value, i, ctypes.byref(diag))
+            success = _unit_diagnostic(self._c_value, i, ctypes.byref(diag))
+            assert success
             result.append(diag._wrap())
         return result
 
@@ -977,8 +978,9 @@ class Token(ctypes.Structure):
         cls._check_token(last)
         first._check_same_unit(last)
         result = _text()
-        assert _token_range_text(ctypes.byref(first), ctypes.byref(last),
-                                 ctypes.byref(result))
+        success = _token_range_text(ctypes.byref(first), ctypes.byref(last),
+                                    ctypes.byref(result))
+        assert success
         return result._wrap() or u''
 
     @property

testsuite/python_support/utils.py

@@ -192,7 +192,8 @@ def build_and_run(grammar=None, py_script=None, ada_main=None, lexer=None,
                   version: str = "undefined",
                   build_date: str = "undefined",
                   full_error_traces: bool = True,
-                  additional_make_args: List[str] = []):
+                  additional_make_args: List[str] = [],
+                  python_args: Optional[List[str]] = None):
     """
     Compile and emit code for `ctx` and build the generated library. Then,
     execute the provided scripts/programs, if any.
@@ -248,6 +249,9 @@ def build_and_run(grammar=None, py_script=None, ada_main=None, lexer=None,
 
     :param additional_make_args: Additional command-line arguments to pass to
         "manage.py make".
+
+    :param python_args: Arguments to pass to the Python interpreter when
+        running a Python script.
     """
     assert not types_from_lkt or lkt_file is not None
 
@@ -362,8 +366,11 @@ def run(*argv, **kwargs):
         # library, we have to use the special Python interpreter the testsuite
         # provides us. See the corresponding code in
         # testuite_support/python_driver.py.
-        python_interpreter = os.environ['PYTHON_INTERPRETER']
-        run(python_interpreter, py_script)
+        args = [os.environ['PYTHON_INTERPRETER']]
+        if python_args:
+            args.extend(python_args)
+        args.append(py_script)
+        run(*args)
 
     if ada_main is not None:
         if isinstance(ada_main, str):

testsuite/tests/python_api/asserts/expected_concrete_syntax.lkt

@@ -0,0 +1,12 @@
+import lexer_example
+@with_lexer(foo_lexer)
+grammar foo_grammar {
+    @main_rule main_rule <- list+(Example("example"))
+
+}
+
+@abstract class FooNode : Node {
+}
+
+class Example : FooNode implements TokenNode {
+}

testsuite/tests/python_api/asserts/main.py

@@ -0,0 +1,19 @@
+import libfoolang
+
+
+print('main.py: Running...')
+
+ctx = libfoolang.AnalysisContext()
+u = ctx.get_from_buffer('foo.txt', b'{example example')
+
+print("Diagnostics:")
+for d in u.diagnostics:
+    print(d)
+print("")
+
+print("Token range:")
+text_range = libfoolang.Token.text_range(u.first_token, u.last_token)
+print(libfoolang._py2to3.text_repr(text_range))
+print("")
+
+print('main.py: Done.')

testsuite/tests/python_api/asserts/test.out

@@ -0,0 +1,9 @@
+main.py: Running...
+Diagnostics:
+1:1-1:2: Expected 'example', got '{'
+
+Token range:
+'{example example'
+
+main.py: Done.
+Done

testsuite/tests/python_api/asserts/test.py

@@ -0,0 +1,26 @@
+"""
+Regression test: check that getting the list of diagnostics and the range of
+text between two tokens works when Python assertions are disabled. This used
+not to work because "operational" code was in assert statements in the Python
+bindings.
+"""
+
+from langkit.dsl import ASTNode
+
+from utils import build_and_run
+
+
+class FooNode(ASTNode):
+    pass
+
+
+class Example(FooNode):
+    token_node = True
+
+
+build_and_run(
+    lkt_file='expected_concrete_syntax.lkt',
+    py_script='main.py',
+    python_args=["-O"],
+)
+print('Done')

testsuite/tests/python_api/asserts/test.yaml

@@ -0,0 +1 @@
+driver: python