Generate non-conflicting qualified Python names

CHANGELOG.md

@@ -13,7 +13,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
  * The compiler will issue a warning when adding any alias that might conflict with any other alias (#1045)
 
 ### Fixed
- * Basilisp now respects the value of Python's `sys.dont_write_bytecode` flag when generating bytecode (#1054)
+ * Fix a bug where Basilisp did not respect the value of Python's `sys.dont_write_bytecode` flag when generating bytecode (#1054)
+ * Fix a bug where Basilisp import names existed in the same namespace as `def` names, which caused some unexpected behavior (#1045)
 
 ## [v0.2.2]
 ### Added

src/basilisp/lang/compiler/analyzer.py

@@ -2595,6 +2595,10 @@ def _import_ast(form: ISeq, ctx: AnalyzerContext) -> Import:
                     "Python module alias must be a symbol", form=f
                 )
             module_alias = module_alias_sym.name
+            if "." in module_alias:
+                raise ctx.AnalyzerException(
+                    "Python module alias must not contain '.'", form=f
+                )
 
             ctx.put_new_symbol(
                 module_alias_sym,

src/basilisp/lang/compiler/generator.py

@@ -1,9 +1,11 @@
 # pylint: disable=too-many-lines
 
 import ast
+import base64
 import collections
 import contextlib
 import functools
+import hashlib
 import logging
 import re
 import uuid
@@ -2275,6 +2277,43 @@ def _if_to_py_ast(ctx: GeneratorContext, node: If) -> GeneratedPyAST[ast.expr]:
     )
 
 
+_IMPORT_HASH_TRANSLATE_TABLE = str.maketrans({"=": "", "+": "", "/": ""})
+
+
+@functools.lru_cache
+def _import_hash(s: str) -> str:
+    """Generate a short, consistent, hash which can be appended to imported module
+    names to effectively separate them from objects of the same name defined in the
+    module.
+
+    Aliases in Clojure exist in a separate "namespace" from interned values, but
+    Basilisp generates Python modules (which are essentially just a single shared
+    namespace), so it is possible that imported module names could clash with `def`'ed
+    names.
+
+    Below, we generate a truncated URL-safe Base64 representation of the MD5 hash of
+    the input string (typically the first '.' delimited component of the potentially
+    qualified module name), removing any '-' characters since those are not safe for
+    Python identifiers.
+
+    The hash doesn't need to be cryptographically secure, but it does need to be
+    consistent across sessions such that when cached namespace modules are reloaded,
+    the new session can find objects generated by the session which generated the
+    cache file. Since we are not concerned with being able to round-trip this data,
+    destructive modifications are not an issue."""
+    digest = hashlib.md5(s.encode()).digest()
+    return base64.b64encode(digest).decode().translate(_IMPORT_HASH_TRANSLATE_TABLE)[:6]
+
+
+def _import_name(root: str, *submodules: str) -> Tuple[str, str]:
+    """Return a tuple of the root import name (with hash suffix) for an import and the
+    full import name (if submodules are provided)."""
+    safe_root = f"{root}_{_import_hash(root)}"
+    if not submodules:
+        return safe_root, safe_root
+    return safe_root, ".".join([safe_root, *submodules])
+
+
 @_with_ast_loc_deps
 def _import_to_py_ast(ctx: GeneratorContext, node: Import) -> GeneratedPyAST[ast.expr]:
     """Return a Python AST node for a Basilisp `import*` expression."""
@@ -2290,10 +2329,11 @@ def _import_to_py_ast(ctx: GeneratorContext, node: Import) -> GeneratedPyAST[ast
         # import if parent and child are both imported:
         #   (import* collections collections.abc)
         if alias.alias is not None:
-            py_import_alias = munge(alias.alias)
+            py_import_alias, _ = _import_name(munge(alias.alias))
             import_func = _IMPORTLIB_IMPORT_MODULE_FN_NAME
         else:
-            py_import_alias = safe_name.split(".", maxsplit=1)[0]
+            py_import_alias, *submodules = safe_name.split(".", maxsplit=1)
+            py_import_alias, _ = _import_name(py_import_alias, *submodules)
             import_func = _BUILTINS_IMPORT_FN_NAME
 
         ctx.symbol_table.context_boundary.new_symbol(
@@ -3268,26 +3308,45 @@ def _interop_prop_to_py_ast(
 
 @_with_ast_loc
 def _maybe_class_to_py_ast(
-    _: GeneratorContext, node: MaybeClass
+    ctx: GeneratorContext, node: MaybeClass
 ) -> GeneratedPyAST[ast.expr]:
-    """Generate a Python AST node for accessing a potential Python module
-    variable name."""
+    """Generate a Python AST node for accessing a potential Python module variable
+    name."""
     assert node.op == NodeOp.MAYBE_CLASS
-    return GeneratedPyAST(
-        node=ast.Name(id=_MODULE_ALIASES.get(node.class_, node.class_), ctx=ast.Load())
-    )
+    if (mod_name := _MODULE_ALIASES.get(node.class_)) is None:
+        current_ns = ctx.current_ns
+
+        # For imported modules only, we should generate the name reference using a
+        # unique, consistent hash name (just as they are imported) to avoid clashing
+        # with names def'ed later in the namespace.
+        name = sym.symbol(node.form.name)
+        if (alias := current_ns.import_aliases.val_at(name)) is not None:
+            _, mod_name = _import_name(munge(alias.name))
+        elif name in current_ns.imports:
+            root, *submodules = node.class_.split(".", maxsplit=1)
+            _, mod_name = _import_name(root, *submodules)
+
+    # Names which are not module references should be passed through.
+    if mod_name is None:
+        mod_name = node.class_
+
+    return GeneratedPyAST(node=ast.Name(id=mod_name, ctx=ast.Load()))
 
 
 @_with_ast_loc
 def _maybe_host_form_to_py_ast(
     _: GeneratorContext, node: MaybeHostForm
 ) -> GeneratedPyAST[ast.expr]:
-    """Generate a Python AST node for accessing a potential Python module
-    variable name with a namespace."""
+    """Generate a Python AST node for accessing a potential Python module variable name
+    with a namespace."""
     assert node.op == NodeOp.MAYBE_HOST_FORM
-    return GeneratedPyAST(
-        node=_load_attr(f"{_MODULE_ALIASES.get(node.class_, node.class_)}.{node.field}")
-    )
+    if (mod_name := _MODULE_ALIASES.get(node.class_)) is None:
+        # At import time, the compiler generates a unique, consistent name for the root
+        # level Python name to avoid clashing with names later def'ed in the namespace.
+        # This is the same logic applied to completing the reference.
+        root, *submodules = node.class_.split(".", maxsplit=1)
+        __, mod_name = _import_name(root, *submodules)
+    return GeneratedPyAST(node=_load_attr(f"{mod_name}.{node.field}"))
 
 
 #########################

tests/basilisp/compiler_test.py

@@ -3311,6 +3311,10 @@ def test_import_module_must_be_symbol(self, lcompile: CompileFn, code: str):
         with pytest.raises(compiler.CompilerException):
             lcompile(code)
 
+    def test_import_alias_may_not_contain_dot(self, lcompile: CompileFn):
+        with pytest.raises(compiler.CompilerException):
+            lcompile("(import* [re :as reg.expr])")
+
     @pytest.mark.parametrize(
         "code",
         [
@@ -6225,6 +6229,48 @@ def test_aliased_namespace_not_hidden_by_python_module(
                 monkeypatch.chdir(cwd)
                 os.unlink(module_file_path)
 
+    @pytest.mark.parametrize(
+        "code",
+        [
+            """
+        (import re)
+
+        (defn re [s]
+          (re/fullmatch #"[A-Z]+" s))
+
+        (re "YES")
+        """,
+            """
+        (import [re :as regex])
+
+        (defn regex [s]
+          (regex/fullmatch #"[A-Z]+" s))
+
+        (regex "YES")
+        """,
+        ],
+    )
+    def test_imports_dont_shadow_def_names(self, lcompile: CompileFn, code: str):
+        match = lcompile(code)
+        assert match is not None
+
+    def test_imports_names_resolve(self, lcompile: CompileFn):
+        import re
+
+        assert lcompile("(import re) re") is re
+        assert lcompile("(import [re :as regex]) regex") is re
+
+        import urllib.parse
+
+        assert (
+            lcompile("(import urllib.parse) urllib.parse/urlparse")
+            is urllib.parse.urlparse
+        )
+        assert (
+            lcompile("(import [urllib.parse :as urlparse]) urlparse/urlparse")
+            is urllib.parse.urlparse
+        )
+
     def test_aliased_var_does_not_resolve(
         self, lcompile: CompileFn, ns: runtime.Namespace
     ):