Handle syntax error in find_imports (#1819)

docs/project/changelog.md

@@ -57,6 +57,10 @@ substitutions:
 - {{Fix}} Fixed a use after free bug in the error handling code.
   {pr}`1816`
 
+- {{Enhancement}} If `find_imports` is used on code that contains a syntax
+  error, it will return an empty list instead of raising a `SyntaxError`.
+  {pr}`1819`
+
 ## Version 0.18.0
 
 _August 3rd, 2021_

src/py/_pyodide/_base.py

@@ -515,7 +515,8 @@ def find_imports(source: str) -> List[str]:
     Returns
     -------
     ``List[str]``
-        A list of module names that are imported in ``source``.
+        A list of module names that are imported in ``source``. If ``source`` is not
+        syntactically correct Python code (after dedenting), returns an empty list.
 
     Examples
     --------
@@ -527,7 +528,10 @@ def find_imports(source: str) -> List[str]:
     # handle mis-indented input from multi-line strings
     source = dedent(source)
 
-    mod = ast.parse(source)
+    try:
+        mod = ast.parse(source)
+    except SyntaxError:
+        return []
     imports = set()
     for node in ast.walk(mod):
         if isinstance(node, ast.Import):

src/tests/test_pyodide.py

@@ -11,16 +11,26 @@ from pyodide import find_imports, eval_code, CodeRunner, should_quiet  # noqa: E
 def test_find_imports():
 
     res = find_imports(
-        dedent(
-            """
-           import numpy as np
-           from scipy import sparse
-           import matplotlib.pyplot as plt
-           """
-        )
+        """
+        import numpy as np
+        from scipy import sparse
+        import matplotlib.pyplot as plt
+        """
     )
     assert set(res) == {"numpy", "scipy", "matplotlib"}
 
+    # If there is a syntax error in the code, find_imports should return empty
+    # list.
+    res = find_imports(
+        """
+        import numpy as np
+        from scipy import sparse
+        import matplotlib.pyplot as plt
+        for x in [1,2,3]
+        """
+    )
+    assert res == []
+
 
 def test_code_runner():
     assert should_quiet("1+1;")