Replace python toolchain with @rules_python #140

furtib · 2026-01-15T07:29:49Z

Why:
We should use an external Python toolchain instead of maintaining our own.
This is necessary mainly for Bazel 8 support.

What:

Replaced the Python toolchain

Addresses:
#108

src/codechecker.bzl

nettle

Thanks for working on Bazel 8, @furtib!
This change is crucial.
At the same time the incompatibility between 8 and 7 and 6 is quite big.
We must be very careful to do not destroy what is working somehow in 6 and 7.
Please do not submit without consensus between all of us.

README.md

src/compile_commands.bzl

.github/platform_environment_setup/rhel9/action.yaml

Szelethus · 2026-01-16T14:15:37Z

src/codechecker.bzl

+            # this script will be run with the python interpreter
            "{Mode}": "Run",
            "{Verbosity}": "DEBUG",
-            "{PythonPath}": python_path,


Are you sure this is needed? Can you explain a little? Is there any precedence for this in other projects?

This was the point of this patch.
Shebangs are always absolute paths!
Bazel, providing its own interpreter/compiler etc, will always give relative paths.
I will look for an example from the wild, but getting rid of the shebang was the main point of this PR.

README.md

nettle

Well, seams like we will have to use rules_python at some point anyway, so we should be ready. And this patch is very good prototype!
However, I'm sure we should split it and move forward very carefully:

Refactor py_runtime to python toolchain at least for Bazel 6 and 7
Make implementation work with all Bazel versions
(theoretically this can be combined, at least partially, with the first step)
Add Bazel 8 support

Before that we must clarify requirements towards rules_python vs bazel_tools in different Bazel versions. As I can understand Bazel 8 still support bazel_tools, but I'm not sure.

nettle · 2026-01-16T20:42:08Z

WORKSPACE

+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")

-register_default_python_toolchain()
+http_archive(
+    name = "rules_python",
+    sha256 = "ca2671529884e3ecb5b79d6a5608c7373a82078c3553b1fa53206e6b9dddab34",
+    strip_prefix = "rules_python-0.38.0",
+    url = "https://github.com/bazelbuild/rules_python/releases/download/0.38.0/rules_python-0.38.0.tar.gz",
+)
+
+load("@rules_python//python:repositories.bzl", "py_repositories")
+
+py_repositories()


What I really dont like is that we add external dependency like this.
In Bazel mod it looks OK, but for Bazel 6 it sucks.

nettle · 2026-01-16T22:35:46Z

src/codechecker.bzl

+        executable = py_toolchain.interpreter,
+        arguments = [ctx.outputs.codechecker_script.path],


Maybe, maybe...

nettle · 2026-01-16T22:38:19Z

src/codechecker.bzl

-            default = "@default_python_tools//:py3_runtime",
-        ),
    },
+    toolchains = ["@rules_python//python:toolchain_type"],


I was also thinking about toolchain, but for some reasons used runtime.
It is definitely good idea to try toolchain again!

nettle · 2026-01-16T22:42:52Z

src/codechecker.bzl

        output = ctx.outputs.codechecker_test_script,
        is_executable = True,
        substitutions = {
+            #"#{Python_path}": py_toolchain.stub_shebang,


This might be interesting!
I did not know about stub_shebang!

I'm not entirely happy with it.
stub_shebang seems to be a static string #!/usr/bin/env python3. (env is not guaranteed to be there)
As I see it, the interpreter is a more lucrative option. Bazel places the interpreter into the sandbox, and we don't have to worry about it at all.

nettle · 2026-01-16T22:43:21Z

src/codechecker.bzl

+    ctx.actions.write(
+        output = ctx.outputs.test_script_wrapper,
+        is_executable = True,
+        content = """
+            {} {}
+        """.format(py_toolchain.interpreter.short_path, ctx.outputs.codechecker_test_script.short_path)
+    )


Oh, this does not look elegant to me!

I agree.
I did this to use the bazel provided python instead of the system-provided (through stub_shebang).

furtib · 2026-01-21T09:31:42Z

I tried to minimize the changes in this patch for easier review.
I currently cannot minimize the changes further, since our own toolchain and the @rules_python one are incompatible with each other.
I understand that the rules_python dependency in the WORKSPACE file is troublesome. I will try to come up with alternatives.

…thod

furtib marked this pull request as ready for review January 15, 2026 07:30

furtib marked this pull request as draft January 15, 2026 07:30

furtib force-pushed the replace-python-toolchain branch 2 times, most recently from bf1da1d to 9fb4c71 Compare January 15, 2026 09:26

furtib changed the title ~~Update python toolchain~~ Bazel 8 support (update python toolchain) Jan 15, 2026

furtib mentioned this pull request Jan 15, 2026

Showcase Bazel 8 support #116

Closed

furtib marked this pull request as ready for review January 15, 2026 10:22

furtib commented Jan 15, 2026

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furtib force-pushed the replace-python-toolchain branch from e49ac73 to 962d110 Compare January 15, 2026 17:40

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furtib force-pushed the replace-python-toolchain branch 4 times, most recently from 605e170 to 8459e07 Compare January 16, 2026 12:21

furtib requested a review from Szelethus January 16, 2026 12:27

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furtib force-pushed the replace-python-toolchain branch 2 times, most recently from f8f3f59 to 5dae841 Compare January 21, 2026 09:24

furtib changed the title ~~Bazel 8 support (update python toolchain)~~ Replace python toolchain with @rules_python Jan 21, 2026

furtib requested review from Szelethus and nettle January 21, 2026 09:31

furtib added 4 commits January 21, 2026 10:41

Update python toolchain

10cd7d8

Fix monolithic test rule

4e2bf3b

Update workspace.template and README.md to reflect current include me…

526753a

…thod

Create wrapper script to use bazel's python interpreter

beb76ea

furtib force-pushed the replace-python-toolchain branch from 5dae841 to beb76ea Compare January 21, 2026 09:41

		executable = py_toolchain.interpreter,
		arguments = [ctx.outputs.codechecker_script.path],

Replace python toolchain with @rules_python #140

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furtib commented Jan 21, 2026

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furtib commented Jan 15, 2026 •

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