Rewrite getpath.c in Python

[zooba]

BPO	45582
Nosy	@ncoghlan, @tiran, @benjaminp, @ambv, @ericsnowcurrently, @zooba, @miss-islington, @neonene, @FFY00
PRs	bpo-45582: Port getpath[p].c to Python #29041 bpo-45582: Fix out-of-tree build issues with new getpath (GH-29902) #29902 bpo-45582: Add conditions to isdir/isfile/isxfile in getpath.c #29906 bpo-45582 Fix prototype of _Py_Get_Getpath_CodeObject. #29907 bpo-45582: Fix signature of _Py_Get_Getpath_CodeObject (GH-29921) #29921 bpo-45582: Fix getpath_isxfile() and test_embed on Windows #29930 bpo-45582: Change the folder location of PGO-instrumented builds on Windows #29941 bpo-45582: framework build: modPath must not be const (GH-29944) #29944 bpo-45582: Ensure PYTHONHOME still overrides detected build prefixes #29948 bpo-45582: Fix framework path and bootstrap build #29954 bpo-45582: Write empty pybuilddir.txt on Windows to allow relocatable build directories #29979 bpo-45582: Fix test_embed failure during a PGO build on Windows #30014 bpo-45582: Don't fail if ENV_PATH is None in getpath.py (GH-31699) #31699

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/zooba'
closed_at = <Date 2021-12-03.00:10:47.332>
created_at = <Date 2021-10-22.23:26:55.306>
labels = ['interpreter-core', 'type-feature', '3.11']
title = 'Rewrite getpath.c in Python'
updated_at = <Date 2022-03-06.19:49:35.401>
user = 'https://github.com/zooba'

bugs.python.org fields:

activity = <Date 2022-03-06.19:49:35.401>
actor = 'christian.heimes'
assignee = 'steve.dower'
closed = True
closed_date = <Date 2021-12-03.00:10:47.332>
closer = 'steve.dower'
components = ['Interpreter Core']
creation = <Date 2021-10-22.23:26:55.306>
creator = 'steve.dower'
dependencies = []
files = []
hgrepos = []
issue_num = 45582
keywords = ['patch']
message_count = 30.0
messages = ['404841', '404843', '405348', '405640', '405641', '405653', '405658', '405731', '405742', '406183', '406184', '406384', '407113', '407322', '407326', '407561', '407562', '407565', '407587', '407604', '407609', '407616', '407720', '407846', '407852', '407881', '407960', '407994', '408226', '414622']
nosy_count = 9.0
nosy_names = ['ncoghlan', 'christian.heimes', 'benjamin.peterson', 'lukasz.langa', 'eric.snow', 'steve.dower', 'miss-islington', 'neonene', 'FFY00']
pr_nums = ['29041', '29902', '29906', '29907', '29921', '29930', '29941', '29944', '29948', '29954', '29979', '30014', '31699']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45582'
versions = ['Python 3.11']

Linked PRs

• gh-89745: Remove commented code in getpath.c #108307
• gh-89745: Remove dead realpath branch in getpath.c #128861
• gh-89745: Remove test_embed.test_init_read_set() #139500

[zooba]

As discussed in bpo-42260, combining the two getpath implementations into a single Python implementation would make it more maintainable and modifiable (particularly where distros need to patch to support alternative layouts).

[zooba]

The PR has more work to do, but the overall layout/changes are more or less there, so happy to discuss feedback/etc.

Obviously there are a lot of edge cases here, but they seem to be mostly tested already. And I think we're early enough in alpha to find any major issues (or absorb any necessary minor changes - seems like trailing slashes might change on some paths).

There are also some changes/hacks into the new frozen module support, so that I can freeze getpath.py without turning it into a module. I really just want to execute the bytecode - no reason for any of its contents to stick around - and this works out pretty neatly. But if the changes to frozen modules seem off then maybe we can split it into totally separate freezing support?

[zooba]

So I think I've found my first completely unavoidable API break: PyConfig_Read(config) has to work before initialisation, but is also supposed to fill out all the fields (including the search path). But because we need at least an interpreter state, we now can't calculate everything.

The only test that seems to be affected here is test_embed.test_init_read_set(), which does a PyConfig_Read() and then inserts new paths into module_search_paths before initialising. With that one skipped, I think everything else can be handled.

[zooba]

Last remaining test failure is one that I can't figure out on my own - the freeze test is rerunning a CPython build (on Linux) and is apparently building getpath.c with the ".c.o" rule rather than the "Modules/getpath.o" rule.

Any tips as to what I should be looking at to figure this one out?

[ericsnowcurrently]

On Wed, Nov 3, 2021 at 1:21 PM Steve Dower <report@bugs.python.org> wrote:

Last remaining test failure is one that I can't figure out on my own - the freeze test is rerunning a CPython build (on Linux) and is apparently building getpath.c with the ".c.o" rule rather than the "Modules/getpath.o" rule.

Any tips as to what I should be looking at to figure this one out?

That test does an out-of-tree build. Might that be related?

[zooba]

I'm betting the out-of-tree (actually just deeper within the same tree) bit is related, but I just can't see how. Modules/getbuildinfo.c takes extra parameters and they seem to be being used, so I can't tell why getpath.c's are not (those rules are listed right next to each other, but well above the .c.o rule).

[zooba]

Unsurprisingly, it was a bad edit that I made to the Makefile myself. The commit that undoes it is aedebcc but since I made the initial change as part of this PR, it was never merged in.

Now to find out why the old getpath could somehow locate the stdlib but new getpath cannot... (I'm guessing it is finding the "original" stdlib rather than the fresh clone, since AFAICT there's no reference at all to the original source dir)