Make IDLE recognize .pyi stub files as source for open, save, and edit

[AlexWaygood]

BPO	45447
Nosy	@terryjreedy, @ronaldoussoren, @zooba, @miss-islington, @E-Paine, @AlexWaygood
PRs	gh-89610: Add syntax highlighting for .pyi files in IDLE #28950 [3.10] bpo-45447: Add syntax highlighting for .pyi files in IDLE (GH-28950) #31303 bpo-45447: Add entry to What's new 3.10 #31304 bpo-45447: Add entry to What's new 3.9 #31305 [3.9] bpo-45447: Add syntax highlighting for .pyi files in IDLE (GH-28950) #31306 bpo-45447: Fix entry in What's New 3.11 #31307 [3.10] bpo-45447: Add entry to What's new 3.10 (GH-31304) #31308 [3.10] bpo-45447: Add entry to What's new 3.9 (GH-31305) #31309 [3.9] bpo-45447: Add entry to What's new 3.9 (GH-31305) #31310

^{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/terryjreedy'
closed_at = None
created_at = <Date 2021-10-12.15:24:36.540>
labels = ['expert-IDLE', 'type-feature', '3.11']
title = 'Make IDLE recognize .pyi stub files as source for open, save, and edit'
updated_at = <Date 2022-02-14.03:35:10.254>
user = 'https://github.com/AlexWaygood'

bugs.python.org fields:

activity = <Date 2022-02-14.03:35:10.254>
actor = 'terry.reedy'
assignee = 'terry.reedy'
closed = False
closed_date = None
closer = None
components = ['IDLE']
creation = <Date 2021-10-12.15:24:36.540>
creator = 'AlexWaygood'
dependencies = []
files = []
hgrepos = []
issue_num = 45447
keywords = ['patch']
message_count = 28.0
messages = ['403738', '403741', '403755', '403772', '403884', '403889', '403915', '403998', '404021', '404023', '404030', '404100', '404102', '404110', '410637', '410669', '412561', '412617', '413147', '413149', '413150', '413156', '413157', '413158', '413168', '413169', '413170', '413211']
nosy_count = 6.0
nosy_names = ['terry.reedy', 'ronaldoussoren', 'steve.dower', 'miss-islington', 'epaine', 'AlexWaygood']
pr_nums = ['28950', '31303', '31304', '31305', '31306', '31307', '31308', '31309', '31310']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue45447'
versions = ['Python 3.11']

Linked PRs

• gh-89610: IDLE: Add util and stub example comments #113222
• [3.12] gh-89610: IDLE: Add util and stub example comments (GH-113222) #113223
• [3.11] gh-89610: IDLE: Add util and stub example comments (GH-113222) #113224

[AlexWaygood]

IDLE currently does not do any syntax highlighting if you use it to open a .pyi stub file, even though everything in a .pyi file is a valid Python expression. It would be great if syntax highlighting for .pyi files could be supported.

[terryjreedy]

It should be fairly easy to recognize x.pyi as a python file. Just have to find the place. Something like
def f(i:int) -> int: ...
would have 'def' and 'int' highlighted.

[AlexWaygood]

It looks like support for .py files is hardcoded into IDLE's source code in the following places:

• browser.ModuleBrowserTreeItem.OnDoubleClick
• browser.ModuleBrowserTreeItem.IsExpandable
• browser.ModuleBrowserTreeItem.listchildren
• editor.ispythonsource << This is the one that controls syntax highlighting
• iomenu.IOBinding.filetypes

If I were to file a PR adding support for .pyi files, would you prefer that I hardcoded ".pyi" in, or would it be better to add a SUPPORTED_FILES constant somewhere?

[terryjreedy]

Thank you for doing the research.

I have been thinking about adding a file containing idlelib 'leaf' objects, those with no idlelib dependencies, which are needed in more than one file. would be to reduce the complexity of the idlelib dependency graph, which has enough cyclic dependencies to make startup tricky. Time to do it. idlelib/common.py?, leaves.py?, or ??? Draft:
---
"""Idlelib objects with no external idlelib dependencies and which are needed in more than one idlelib module. They are included here because a) they don't particularly belong elsewhere or b) because inclusion here simplifies the idlelib dependency graph.

TODO: Python versions (editor and help_about), tk version and patchlevel (pyshell, help_about, maxos?, editor?), std streams (pyshell, run), warning stuff (ditto).
"""

# python_extensions is used in editor, browser, and iomenu.
# .pyw is for Windows; .pyi is for stub files.
python_extensions = ('.py', '.pyw', '.pyi')  
extension_string = "*" + " *".join(python_extensions)

---

editor.EditorWindow.ispythonsource could be moved into the new file if a 'firstline=None' argument were added.

OnDoubleClick should use IsExpandable. IsExpandable should use the logic in ispythonsource so Linux no-extension python source can be browsed as well as edited.

After manual testing, add a new test_common.py file in idlelib.idle_test. After imports, it could start with one test:

class ExtensionTest(TestCase):
    def test_stub(self):
        self.assertIn('.pyi', common.python_extensions)
        self.assertIn('.pyi', common.extension_string)

For IDLE, I can and will backport.

[terryjreedy]

I am going to call the file util.py and will work on a PR.

[AlexWaygood]

Oh — I've already nearly finished a PR. Do you mind if I submit mine? Happy to make any changes you like, obviously.