Generate main.py so we can get independent of ipython

Author: philsc

python/bin/BUILD.bazel

@@ -1,4 +1,5 @@
 load("//python/private:interpreter.bzl", _interpreter_binary = "interpreter_binary")
+load("//python/private:repl.bzl", "generate_repl_main")
 load("//python:py_binary.bzl", "py_binary")
 
 filegroup(
@@ -24,27 +25,38 @@ label_flag(
     build_setting_default = "//python:none",
 )
 
+generate_repl_main(
+    name = "repl_py",
+    out = "repl.py",
+    src = "repl_stub.py",
+)
+
+label_flag(
+    name = "repl_stub",
+    build_setting_default = "repl_stub.py",
+)
+
+# The user can modify this flag to make an interpreter shell library available
+# for the stub. E.g. if they switch the stub for an ipython-based on, then they
+# can point this at their version of ipython.
+label_flag(
+    name = "repl_stub_dep",
+    build_setting_default = "//python/private:empty",
+)
+
 py_binary(
     name = "repl",
-    srcs = ["repl.py"],
+    srcs = [":repl.py"],
     deps = [
+        ":repl_stub_dep",
         ":repl_dep",
-        ":repl_lib_dep",
     ],
     visibility = ["//visibility:public"],
 )
 
-# The user can modify this flag to make arbitrary libraries available for import
-# on the REPL. Anything that exposes PyInfo can be used here.
+# The user can modify this flag to make arbitrary PyInfo targets available for
+# import on the REPL.
 label_flag(
     name = "repl_dep",
-    build_setting_default = "//python:none",
-)
-
-# The user can modify this flag to make additional libraries available
-# specifically for the purpose of interacting with the REPL. For example, point
-# this at ipython in your .bazelrc file.
-label_flag(
-    name = "repl_lib_dep",
-    build_setting_default = "//python:none",
+    build_setting_default = "//python/private:empty",
 )

python/bin/repl_stub.py

@@ -0,0 +1,2 @@
+import code
+code.interact(local=dict(globals(), **locals()))

python/private/BUILD.bazel

@@ -789,6 +789,13 @@ py_library(
     ],
 )
 
+py_binary(
+    name = "repl_main_generator",
+    srcs = [
+        "repl_main_generator.py",
+    ],
+)
+
 # The current toolchain's interpreter as an excutable, usable with
 # executable=True attributes.
 current_interpreter_executable(
@@ -798,6 +805,10 @@ current_interpreter_executable(
     visibility = ["//visibility:public"],
 )
 
+py_library(
+    name = "empty",
+)
+
 sentinel(
     name = "sentinel",
 )

python/private/repl.bzl

@@ -0,0 +1,39 @@
+def _generate_repl_main_impl(ctx):
+    args = ctx.actions.args()
+    args.add_all([
+        ctx.file._template,
+        ctx.file.src,
+        ctx.outputs.out,
+    ])
+
+    ctx.actions.run(
+        executable = ctx.executable._generator,
+        inputs = [
+            ctx.file._template,
+            ctx.file.src,
+        ],
+        outputs = [ctx.outputs.out],
+        arguments = [args],
+    )
+
+generate_repl_main = rule(
+    implementation = _generate_repl_main_impl,
+    attrs = {
+        "out": attr.output(
+            mandatory = True,
+        ),
+        "src": attr.label(
+            mandatory = True,
+            allow_single_file = True,
+        ),
+        "_template": attr.label(
+            default = "//python/private:repl_template.py",
+            allow_single_file = True,
+        ),
+        "_generator": attr.label(
+            default = "//python/private:repl_main_generator",
+            executable = True,
+            cfg = "exec",
+        ),
+    },
+)

python/private/repl_main_generator.py

@@ -0,0 +1,27 @@
+import sys
+import textwrap
+from pathlib import Path
+
+LINE_TO_REPLACE = """\
+    pass # %REPLACE_WHOLE_LINE_WITH_STUB%
+"""
+
+def main(argv):
+    template = Path(sys.argv[1])
+    stub = Path(sys.argv[2])
+    output = Path(sys.argv[3])
+
+    template_text = template.read_text()
+    stub_text = stub.read_text()
+
+    indented_stub_text = textwrap.indent(stub_text, " " * 4)
+
+    output_text = template_text.replace(LINE_TO_REPLACE, indented_stub_text)
+    if template_text == output_text:
+        raise ValueError("Failed to find the following in the template: {LINE_TO_REPLACE}")
+
+    output.write_text(output_text)
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv))

python/bin/repl.py renamed to python/private/repl_template.py

@@ -1,11 +1,10 @@
 import os
 from pathlib import Path
 
-def start_repl():
-    # Point libedit/readline at the correct terminfo databases.
-    # https://github.com/astral-sh/python-build-standalone/blob/f0abfc9cb1f6a985fc5561cf5435f7f6e8a64e5b/docs/quirks.rst#backspace-key-doesnt-work-in-python-repl
-    os.environ["TERMINFO_DIRS"] = "/etc/terminfo:/lib/terminfo:/usr/share/terminfo"
+def repl_stub():
+    pass # %REPLACE_WHOLE_LINE_WITH_STUB%
 
+def start_repl():
     # Simulate Python's behavior when a valid startup script is defined by the
     # PYTHONSTARTUP variable. If this file path fails to load, print the error
     # and revert to the default behavior.
@@ -18,15 +17,7 @@ def start_repl():
             compiled_code = compile(source_code, filename=startup_file, mode="exec")
             eval(compiled_code, {})
 
-    try:
-        # If the user has made ipython available somehow (e.g. via
-        # `repl_lib_dep`), then use it.
-        import IPython
-        IPython.start_ipython()
-    except ModuleNotFoundError:
-        # Fall back to the default shell.
-        import code
-        code.interact(local=dict(globals(), **locals()))
+    repl_stub()
 
 if __name__ == "__main__":
     start_repl()