gh-105938: Emit a SyntaxWarning for escaped braces in an f-string

[lysnikolaou]

• Issue: DeprecationWarning when escaping curly braces in an f-string #105938

[miss-islington]

Thanks @lysnikolaou for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12.
🐍🍒⛏🤖

[bedevere-bot]

GH-105941 is a backport of this pull request to the 3.12 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot AMD64 Arch Linux TraceRefs 3.x has failed when building commit 6586cee.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/all/#builders/484/builds/3515) and take a look at the build logs.
4. Check if the failure is related to this commit (6586cee) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/all/#builders/484/builds/3515

Failed tests:

• test_capi

Summary of the results of the build (if available):

==

Click to see traceback logs

remote: Enumerating objects: 8, done.        
remote: Counting objects:  12% (1/8)        
remote: Counting objects:  25% (2/8)        
remote: Counting objects:  37% (3/8)        
remote: Counting objects:  50% (4/8)        
remote: Counting objects:  62% (5/8)        
remote: Counting objects:  75% (6/8)        
remote: Counting objects:  87% (7/8)        
remote: Counting objects: 100% (8/8)        
remote: Counting objects: 100% (8/8), done.        
remote: Compressing objects:  14% (1/7)        
remote: Compressing objects:  28% (2/7)        
remote: Compressing objects:  42% (3/7)        
remote: Compressing objects:  57% (4/7)        
remote: Compressing objects:  71% (5/7)        
remote: Compressing objects:  85% (6/7)        
remote: Compressing objects: 100% (7/7)        
remote: Compressing objects: 100% (7/7), done.        
remote: Total 8 (delta 1), reused 4 (delta 1), pack-reused 0        
From https://github.com/python/cpython
 * branch                  main       -> FETCH_HEAD
Note: switching to '6586cee27f32f0354fe4e77c7b8c6e399329b5e2'.

You are in 'detached HEAD' state. You can look around, make experimental
changes and commit them, and you can discard any commits you make in this
state without impacting any branches by switching back to a branch.

If you want to create a new branch to retain commits you create, you may
do so (now or later) by using -c with the switch command. Example:

  git switch -c <new-branch-name>

Or undo this operation with:

  git switch -

Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at 6586cee27f gh-105938: Emit a SyntaxWarning for escaped braces in an f-string (#105939)
Switched to and reset branch 'main'

Objects/object.c:2197: _Py_ForgetReference: Assertion failed: invalid object chain
Enable tracemalloc to get the memory block allocation traceback

object address  : 0x7fb9e3fd88f0
object refcount : 0
object type     : 0x55f67349d660
object type name: tuple
object repr     : <refcnt 0 at 0x7fb9e3fd88f0>

Fatal Python error: _PyObject_AssertFailed: _PyObject_AssertFailed
Python runtime state: initialized

Current thread 0x00007fb9f19d7740 (most recent call first):
  File "<string>", line 3 in <module>

Extension modules: _testinternalcapi (total: 1)
Debug memory block at address p=0x7fb9f18fdce0: API '�'
    18302063728033390045 bytes originally requested
    The 7 pad bytes at p-7 are not all FORBIDDENBYTE (0xfd):
        at p-7: 0xdd *** OUCH
        at p-6: 0xdd *** OUCH
        at p-5: 0xdd *** OUCH
        at p-4: 0xdd *** OUCH
        at p-3: 0xdd *** OUCH
        at p-2: 0xdd *** OUCH
        at p-1: 0xdd *** OUCH
    Because memory is corrupted at the start, the count of bytes requested
       may be bogus, and checking the trailing pad bytes may segfault.
    The 8 pad bytes at tail=0xfdfe7db7ef8dbabd are Fatal Python error: Segmentation fault

Current thread 0x00007fb9f19d7740 (most recent call first):
  File "<string>", line 3 in <module>

Extension modules: _testcapi, _testmultiphase, _testsinglephase, _xxsubinterpreters, _testinternalcapi (total: 5)
make: *** [Makefile:2009: buildbottest] Segmentation fault (core dumped)

Cannot open file '/buildbot/buildarea/3.x.pablogsal-arch-x86_64/build/test-results.xml' for upload