Prefer using the module loader to get source in builder. (#1207)

* Use loader.get_source() in builder.module_build()

Otherwise we fail to get the module source code when running in an
embedded hermetic interpreter environment where the source does not
live on a filesystem.

Co-authored-by: Pierre Sassoulas <[email protected]>

Author: gpshead

ChangeLog

@@ -12,6 +12,12 @@ What's New in astroid 2.9.1?
 ============================
 Release date: TBA
 
+* Prefer the module loader get_source() method in AstroidBuilder's
+  module_build() when possible to avoid assumptions about source
+  code being available on a filesystem.  Otherwise the source cannot
+  be found and application behavior changes when running within an
+  embedded hermetic interpreter environment (pyoxidizer, etc.).
+
 * Require Python 3.6.2 to use astroid.
 
 * Fix ``deque.insert()`` signature in ``collections`` brain.

astroid/builder.py

@@ -87,7 +87,15 @@ def module_build(
         """Build an astroid from a living module instance."""
         node = None
         path = getattr(module, "__file__", None)
-        if path is not None:
+        loader = getattr(module, "__loader__", None)
+        # Prefer the loader to get the source rather than assuming we have a
+        # filesystem to read the source file from ourselves.
+        if loader:
+            modname = modname or module.__name__
+            source = loader.get_source(modname)
+            if source:
+                node = self.string_build(source, modname, path=path)
+        if node is None and path is not None:
             path_, ext = os.path.splitext(modutils._path_from_filename(path))
             if ext in {".py", ".pyc", ".pyo"} and os.path.exists(path_ + ".py"):
                 node = self.file_build(path_ + ".py", modname)