Sync pre-release CPython 3.15 branch from GitHub (2026-07-13)

Summary:
Imported python/cpython `3.15.0b3+dev` from upstream rev [`9efded4`](https://www.github.com/python/cpython/commit/9efded46646ae25de8e8c6fdef85f2f7d188dfd3) (committed 2026-07-13 10:09:39+00:00).

# Commit Info

- Base: (`3.15.0b3+dev`) - [`cb912e1`](https://www.github.com/python/cpython/commit/cb912e108c590bb0b8ded55653e63ad47f945362) (commit date: 2026-07-10 02:49:38+00:00)
- Imported: (`3.15.0b3+dev`) - [`9efded4`](https://www.github.com/python/cpython/commit/9efded46646ae25de8e8c6fdef85f2f7d188dfd3) (commit date: 2026-07-13 10:09:39+00:00)

# Noteworthy file changes

- Native files (3 added):
  ```
  + Modules/expat/fallthrough.h
  + Modules/expat/memory_sanitizer.h
  + Modules/expat/xcsinc.c
  ```
- Low-signal files (10 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GC6koyIgfArMYCkDAG1CjHZN-KBAbr0LAAAz

Reviewed By: yoney

Differential Revision: D111729699

fbshipit-source-id: 76b7dadb8f03d88731a68923a45f0a59b438a9c9

Author: itamaro

.github/actionlint.yaml

@@ -1,5 +1,12 @@
 config-variables: null
 
+# Pending release of actionlint > 1.7.12 for ubuntu-26.04* support:
+# https://github.com/rhysd/actionlint/pull/683
+self-hosted-runner:
+  labels:
+    - ubuntu-26.04
+    - ubuntu-26.04-arm
+
 paths:
   .github/workflows/**/*.yml:
      ignore:

.github/workflows/add-issue-header.yml

@@ -17,7 +17,7 @@ permissions:
 
 jobs:
   add-header:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     permissions:
       issues: write
     timeout-minutes: 5

.github/workflows/build.yml

@@ -100,7 +100,7 @@ jobs:
     name: 'Check if Autoconf files are up to date'
     # Don't use ubuntu-latest but a specific version to make the job
     # reproducible: to get the same tools versions (autoconf, aclocal, ...)
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     container:
       image: ghcr.io/python/autoconf:2025.01.02.12581854023
     timeout-minutes: 60
@@ -143,7 +143,7 @@ jobs:
     name: 'Check if generated files are up to date'
     # Don't use ubuntu-latest but a specific version to make the job
     # reproducible: to get the same tools versions (autoconf, aclocal, ...)
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     needs: build-context
     if: needs.build-context.outputs.run-tests == 'true'
@@ -286,18 +286,18 @@ jobs:
         - false
         - true
         os:
-        - ubuntu-24.04
-        - ubuntu-24.04-arm
+        - ubuntu-26.04
+        - ubuntu-26.04-arm
         exclude:
         # Do not test BOLT with free-threading, to conserve resources
         - bolt: true
           free-threading: true
         # BOLT currently crashes during instrumentation on aarch64
-        - os: ubuntu-24.04-arm
+        - os: ubuntu-26.04-arm
           bolt: true
         include:
         # Enable CPU-intensive tests on ARM (default build only)
-        - os: ubuntu-24.04-arm
+        - os: ubuntu-26.04-arm
           bolt: false
           free-threading: false
           test-opts: '-u cpu'
@@ -317,7 +317,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-24.04]
+        os: [ubuntu-26.04]
         ssllib:
           # See Tools/ssl/make_ssl_data.py for notes on adding a new version
           ## OpenSSL
@@ -393,7 +393,7 @@ jobs:
           - arch: aarch64
             runs-on: macos-26
           - arch: x86_64
-            runs-on: ubuntu-24.04
+            runs-on: ubuntu-26.04
 
     runs-on: ${{ matrix.runs-on }}
     steps:
@@ -440,7 +440,7 @@ jobs:
 
   test-hypothesis:
     name: "Hypothesis tests on Ubuntu"
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     needs: build-context
     if: needs.build-context.outputs.run-ubuntu == 'true'
@@ -551,7 +551,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-24.04]
+        os: [ubuntu-26.04]
     env:
       OPENSSL_VER: 3.5.7
       PYTHONSTRICTEXTENSIONBUILD: 1
@@ -601,6 +601,7 @@ jobs:
         - Thread
         free-threading:
         - false
+        - true
         sanitizer:
         - TSan
         include:
@@ -612,20 +613,9 @@ jobs:
       sanitizer: ${{ matrix.sanitizer }}
       free-threading: ${{ matrix.free-threading }}
 
-  # XXX: Temporarily allow this job to fail to not block PRs.
-  build-san-free-threading:
-    # ${{ '' } is a hack to nest jobs under the same sidebar category.
-    name: Sanitizers${{ '' }}  # zizmor: ignore[obfuscation]
-    needs: build-context
-    if: needs.build-context.outputs.run-ubuntu == 'true'
-    uses: ./.github/workflows/reusable-san.yml
-    with:
-      sanitizer: TSan
-      free-threading: true
-
   cross-build-linux:
     name: Cross build Linux
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     needs: build-context
     if: needs.build-context.outputs.run-ubuntu == 'true'
@@ -726,7 +716,6 @@ jobs:
     - test-hypothesis
     - build-asan
     - build-san
-    - build-san-free-threading
     - cross-build-linux
     - cifuzz
     if: always()
@@ -738,7 +727,6 @@ jobs:
         allowed-failures: >-
           build-android,
           build-emscripten,
-          build-san-free-threading,
           build-windows-msi,
           build-ubuntu-ssltests,
           test-hypothesis,

.github/workflows/jit.yml

@@ -29,7 +29,7 @@ env:
 jobs:
   interpreter:
     name: Interpreter (Debug)
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
@@ -145,9 +145,9 @@ jobs:
           - false
         include:
           - target: x86_64-unknown-linux-gnu/gcc
-            runner: ubuntu-24.04
+            runner: ubuntu-26.04
           - target: aarch64-unknown-linux-gnu/gcc
-            runner: ubuntu-24.04-arm
+            runner: ubuntu-26.04-arm
     steps:
       - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
         with:
@@ -160,8 +160,7 @@ jobs:
           sudo ./.github/workflows/posix-deps-apt.sh
       - name: Build
         run: |
-          sudo bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)" ./llvm.sh ${{ env.LLVM_VERSION }}
-          export PATH="$(llvm-config-${{ env.LLVM_VERSION }} --bindir):$PATH"
+          # On ubuntu-26.04 image, clang is clang-21 by default
           ./configure --enable-experimental-jit ${{ matrix.debug && '--with-pydebug' || '' }}
           make all --jobs 4
       - name: Test
@@ -171,7 +170,7 @@ jobs:
   linux-extras:
     name: ${{ matrix.name }}
 
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     strategy:
       fail-fast: false
@@ -202,8 +201,7 @@ jobs:
           sudo ./.github/workflows/posix-deps-apt.sh
       - name: Build
         run: |
-          sudo bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)" ./llvm.sh ${{ env.LLVM_VERSION }}
-          export PATH="$(llvm-config-${{ env.LLVM_VERSION }} --bindir):$PATH"
+          # On ubuntu-26.04 image, clang is clang-21 by default
           if [ "${{ matrix.use_clang }}" = "true" ]; then
             export CC=clang-${{ env.LLVM_VERSION }}
           fi

.github/workflows/new-bugs-announce-notifier.yml

@@ -10,7 +10,7 @@ permissions:
 
 jobs:
   notify-new-bugs-announce:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     permissions:
       issues: read
     timeout-minutes: 10

.github/workflows/posix-deps-apt.sh

@@ -5,37 +5,23 @@ apt-get -yq --no-install-recommends install \
     build-essential \
     pkg-config \
     cmake \
+    curl \
     gdb \
     lcov \
     libb2-dev \
     libbz2-dev \
     libffi-dev \
-    libgdbm-dev \
     libgdbm-compat-dev \
+    libgdbm-dev \
     liblzma-dev \
+    libmpdec-dev \
     libncurses5-dev \
     libreadline6-dev \
     libsqlite3-dev \
     libssl-dev \
     libzstd-dev \
-    lzma \
-    lzma-dev \
     strace \
     tk-dev \
     uuid-dev \
     xvfb \
     zlib1g-dev
-
-# Workaround missing libmpdec-dev on ubuntu 24.04 by building mpdecimal
-# from source. ppa:ondrej/php (launchpad.net) are unreliable 
-# (https://status.canonical.com) so fetch the tarball directly
-# from the upstream host.
-# https://www.bytereef.org/mpdecimal/
-MPDECIMAL_VERSION=4.0.1
-curl -fsSL "https://www.bytereef.org/software/mpdecimal/releases/mpdecimal-${MPDECIMAL_VERSION}.tar.gz" \
-    | tar -xz -C /tmp
-(cd "/tmp/mpdecimal-${MPDECIMAL_VERSION}" \
-    && ./configure --prefix=/usr/local \
-    && make -j"$(nproc)" \
-    && make install)
-ldconfig

.github/workflows/require-pr-label.yml

@@ -11,7 +11,7 @@ jobs:
   label-dnm:
     name: DO-NOT-MERGE
     if: github.repository_owner == 'python'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     permissions:
       pull-requests: read
     timeout-minutes: 10
@@ -28,7 +28,7 @@ jobs:
   label-reviews:
     name: Unresolved review
     if: github.repository_owner == 'python'
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-slim
     permissions:
       pull-requests: read
     timeout-minutes: 10

.github/workflows/reusable-docs.yml

@@ -106,7 +106,7 @@ jobs:
   # Run "doctest" on HEAD as new syntax doesn't exist in the latest stable release
   doctest:
     name: 'Doctest'
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

.github/workflows/reusable-emscripten.yml

@@ -12,7 +12,7 @@ env:
 jobs:
   build-emscripten-reusable:
     name: 'build and test'
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 40
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2

.github/workflows/reusable-san.yml

@@ -27,7 +27,7 @@ jobs:
         && ' (free-threading)'
         || ''
       }}
-    runs-on: ubuntu-24.04
+    runs-on: ubuntu-26.04
     timeout-minutes: 60
     steps:
     - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
@@ -38,14 +38,7 @@ jobs:
     - name: Install dependencies
       run: |
         sudo ./.github/workflows/posix-deps-apt.sh
-        # Install clang
-        wget https://apt.llvm.org/llvm.sh
-        chmod +x llvm.sh
-        sudo ./llvm.sh 21
-        sudo update-alternatives --install /usr/bin/clang clang /usr/bin/clang-21 100
-        sudo update-alternatives --set clang /usr/bin/clang-21
-        sudo update-alternatives --install /usr/bin/clang++ clang++ /usr/bin/clang++-21 100
-        sudo update-alternatives --set clang++ /usr/bin/clang++-21
+        # On ubuntu-26.04 image, clang is clang-21 by default
         echo "CC=clang" >> "$GITHUB_ENV"
         echo "CXX=clang++" >> "$GITHUB_ENV"
     - name: TSan option setup