Python: Add example of top-level module shadowing stdlib (v2)

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/LocalModuleWithRef.ql

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+import python
+
+from ModuleValue mv, ControlFlowNode ref, string local_external
+where
+  ref = mv.getAReference() and
+  exists(mv.getScope().getFile().getRelativePath()) and
+  (
+    if exists(ref.getLocation().getFile().getRelativePath())
+    then local_external = "local"
+    else local_external = "external"
+  )
+select "Local module", mv, "referenced in " + local_external + " file called",
+  ref.getLocation().getFile().getShortName()

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/LocalModules.expected

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+| code-invalid-package-name/cmd.py:0:0:0:0 | Script cmd.py |
+| code-invalid-package-name/test_fail.py:0:0:0:0 | Script test_fail.py |
+| code-invalid-package-name/test_ok.py:0:0:0:0 | Script test_ok.py |
+| code-invalid-package-name/unique_name.py:0:0:0:0 | Script unique_name.py |
+| code-invalid-package-name/unique_name_use.py:0:0:0:0 | Script unique_name_use.py |

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/LocalModules.ql

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+import python
+
+from Module m
+where exists(m.getFile().getRelativePath())
+select m

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/ModuleWithLocalRef.expected

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+| Module 'cmd' (external, in stdlib, not missing) referenced in local file | code-invalid-package-name/test_ok.py:1 |
+| Module 'pdb' (external, in stdlib, not missing) referenced in local file | code-invalid-package-name/test_fail.py:3 |
+| Module 'unique_name' (external, not in stdlib, missing) referenced in local file | code-invalid-package-name/unique_name_use.py:1 |

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/ModuleWithLocalRef.ql

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+import python
+
+from ModuleValue mv, ControlFlowNode ref, string in_stdlib, string local_external, string is_missing
+where
+  ref = mv.getAReference() and
+  exists(ref.getLocation().getFile().getRelativePath()) and
+  (
+    if mv.getScope().getFile().inStdlib()
+    then in_stdlib = "in stdlib"
+    else in_stdlib = "not in stdlib"
+  ) and
+  (
+    if exists(mv.getScope().getFile().getRelativePath())
+    then local_external = "local"
+    else local_external = "external"
+  ) and
+  (if mv.isAbsent() then is_missing = "missing" else is_missing = "not missing")
+select "Module '" + mv.getName() + "' (" + local_external + ", " + in_stdlib + ", " + is_missing +
+    ") referenced in local file", ref.getLocation().toString()

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/README.md

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+This test shows how we handle modules that shadow a module in the standard library.
+
+We manually replicate the behavior of `codeql database create --source-root <src-dir>`, which will use `-R <src-dir>`. By default, the way qltest invokes the extractor will cause different behavior. Therefore, we also need to move our code outside of the top-level folder, and it lives in `code-invalid-package-name/` -- notice that if we use `code` as the folder name, the extractor will treat it as if there is a package called `code` (note, `codeql database create` would not treat the folder `code` as a package when `code` is used as the `--source-root`).
+
+The results from `LocalModules.ql`, where everything is a script, matches with the extractor :+1:
+
+Because we have a `cmd.py` file, whenever the python interpreter sees `import cmd`, that is the file that will be used!
+
+* `python test_ok.py` works as intended, and prints `Foo`
+* `python test_fail.py` raises an exception, since it imports `pdb.py` from the standard library, which (at least in Python 3.8) tries to import `cmd.py` from the standard library, but instead is served our `cmd.py` module. Therefore it fails with `AttributeError: module 'cmd' has no attribute 'Cmd'`

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code-invalid-package-name/cmd.py

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+foo = "Foo"
+print("my own cmd imported")

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code-invalid-package-name/test_fail.py

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+# we import `pdb` which import the `cmd` module from the standard library
+# and allows us to set --max-import-depth=2, to make the test run fast
+import pdb

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code-invalid-package-name/test_ok.py

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+from cmd import foo
+print(foo)

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code-invalid-package-name/unique_name.py

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+foo = "Foo"

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/code-invalid-package-name/unique_name_use.py

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+from unique_name import foo
+print(foo)

python/ql/test/library-tests/PointsTo/regressions/wrong/module-imports/conflict-stdlib/options

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+semmle-extractor-options: --max-import-depth=2 -R code-invalid-package-name/