fix: tab completion for REPL

fixes #3090

Author: jpwoodbu

python/bin/repl_stub.py

@@ -17,8 +17,27 @@
 console_locals = globals().copy()
 
 import code
+import readline
+import rlcompleter
 import sys
 
+class DynamicCompleter(rlcompleter.Completer):
+    """
+    A custom completer that dynamically updates its namespace to include new
+    imports made within the interactive session.
+    """
+    def __init__(self, namespace):
+        # Store a reference to the namespace, not a copy, so that changes to the namespace are
+        # reflected.
+        self.namespace = namespace
+
+    def complete(self, text, state):
+        # Update the completer's internal namespace with the current interactive session's locals
+        # and globals.  This is the key to making new imports discoverable.
+        rlcompleter.Completer.__init__(self, self.namespace)
+        return super().complete(text, state)
+
+
 if sys.stdin.isatty():
     # Use the default options.
     exitmsg = None
@@ -28,5 +47,18 @@
     sys.ps1 = ""
     sys.ps2 = ""
 
+# Set up tab completion.
+completer = DynamicCompleter(console_locals)
+readline.set_completer(completer.complete)
+
+# TODO(jpwoodbu): Use readline.backend instead of readline.__doc__ once we can depend on having
+# Python >=3.13.
+if 'libedit' in readline.__doc__: # type: ignore
+    readline.parse_and_bind("bind ^I rl_complete")
+elif 'GNU readline' in readline.__doc__: # type: ignore
+    readline.parse_and_bind("tab: complete")
+else:
+    print('Could not enable tab completion!')
+
 # We set the banner to an empty string because the repl_template.py file already prints the banner.
 code.interact(local=console_locals, banner="", exitmsg=exitmsg)

python/private/repl.bzl

@@ -1,10 +1,12 @@
 """Implementation of the rules to expose a REPL."""
 
 load("//python:py_binary.bzl", _py_binary = "py_binary")
+load("@bazel_skylib//lib:paths.bzl", "paths")
 
 def _generate_repl_main_impl(ctx):
     stub_repo = ctx.attr.stub.label.repo_name or ctx.workspace_name
-    stub_path = "/".join([stub_repo, ctx.file.stub.short_path])
+    unnormalized_path = "/".join([stub_repo, ctx.file.stub.short_path])
+    stub_path = paths.normalize(unnormalized_path)
 
     out = ctx.actions.declare_file(ctx.label.name + ".py")