Sync pre-release CPython 3.15 branch from GitHub (2026-08-10)

Summary:
Imported python/cpython `3.15.0rc1+dev` from upstream rev [`2396815`](https://www.github.com/python/cpython/commit/2396815da3ed2993cac5f13c59f749b3057ae83f) (committed 2026-08-10 17:04:58+00:00).

# Commit Info

- Base: (`3.15.0rc1+dev`) - [`a1ab3b0`](https://www.github.com/python/cpython/commit/a1ab3b0024d1d08eca35d63454a678c9a11b29a0) (commit date: 2026-08-08 04:34:08+00:00)
- Imported: (`3.15.0rc1+dev`) - [`2396815`](https://www.github.com/python/cpython/commit/2396815da3ed2993cac5f13c59f749b3057ae83f) (commit date: 2026-08-10 17:04:58+00:00)

# Noteworthy file changes

- Low-signal files (2 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GMUkRBnpG1-ZPjYGACEhiWH6DjgHbr0LAAAz

Differential Revision: D115531006

fbshipit-source-id: 779bb9a26d0a5ee9b05c0c73b1ac3aa323f2d034

Author: generatedunixname1734921407115435

.github/workflows/build.yml

@@ -308,6 +308,12 @@ jobs:
       os: ${{ matrix.os }}
       test-opts: ${{ matrix.test-opts || '' }}
 
+  build-ubuntu-installed:
+    name: 'Ubuntu (installed)'
+    needs: build-context
+    if: needs.build-context.outputs.run-ubuntu == 'true'
+    uses: ./.github/workflows/reusable-install.yml
+
   build-ubuntu-ssltests:
     name: 'Ubuntu SSL tests'
     runs-on: ${{ matrix.os }}
@@ -700,6 +706,7 @@ jobs:
     - build-windows-msi
     - build-macos
     - build-ubuntu
+    - build-ubuntu-installed
     - build-ubuntu-ssltests
     - build-ios
     - build-emscripten
@@ -750,6 +757,7 @@ jobs:
             !fromJSON(needs.build-context.outputs.run-ubuntu)
             && '
             build-ubuntu,
+            build-ubuntu-installed,
             build-ubuntu-ssltests,
             test-hypothesis,
             build-asan,

.github/workflows/reusable-install.yml

@@ -0,0 +1,44 @@
+name: Reusable Ubuntu (installed)
+
+on:
+  workflow_call:
+
+permissions:
+  contents: read
+
+env:
+  FORCE_COLOR: 1
+
+jobs:
+  build-install-test:
+    name: build, install and test
+    runs-on: ubuntu-26.04-arm
+    timeout-minutes: 60
+    env:
+      PYTHONSTRICTEXTENSIONBUILD: 1
+    steps:
+    - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
+      with:
+        persist-credentials: false
+    - name: Register gcc problem matcher
+      run: echo "::add-matcher::.github/problem-matchers/gcc.json"
+    - name: Set install dir
+      run:
+        echo "INSTALL_DIR=$(realpath "${GITHUB_WORKSPACE}/../installed-python")" >> "$GITHUB_ENV"
+    - name: Install dependencies
+      run: sudo ./.github/workflows/posix-deps-apt.sh
+    - name: Configure CPython
+      run: ./configure --config-cache --prefix="$INSTALL_DIR"
+    - name: Build CPython
+      run: make -j
+    - name: Install CPython
+      run: make install
+    - name: Set installed interpreter
+      run: |
+        ldversion=$(./python -c 'import sysconfig; print(sysconfig.get_config_var("LDVERSION"))')
+        echo "INSTALLED_PYTHON=${INSTALL_DIR}/bin/python${ldversion}" >> "$GITHUB_ENV"
+    - name: Display build info
+      run: |
+        "$INSTALLED_PYTHON" -m test.pythoninfo
+    - name: Test the installed Python
+      run: xvfb-run "$INSTALLED_PYTHON" -m test --fast-ci --timeout=900

Lib/profiling/sampling/_flamegraph_assets/flamegraph.js

@@ -99,13 +99,23 @@ function getDisplayName(moduleName, filename) {
   return filename;
 }
 
-function selectFlamegraphData() {
-  const baseData = isShowingElided ? elidedFlamegraphData : normalData;
+function selectFlamegraphData(selectedThreadId = null) {
+  let baseData = isShowingElided ? elidedFlamegraphData : normalData;
+
+  if (selectedThreadId !== null) {
+    baseData = filterDataByThread(baseData, selectedThreadId);
+  }
 
   if (!isInverted) {
     return baseData;
   }
 
+  // Thread-filtered trees have different values, so invert them after filtering
+  // instead of using the cached all-thread tree.
+  if (selectedThreadId !== null) {
+    return generateInvertedFlamegraph(baseData);
+  }
+
   if (isShowingElided) {
     if (!invertedElidedData) {
       invertedElidedData = generateInvertedFlamegraph(baseData);
@@ -120,12 +130,11 @@ function selectFlamegraphData() {
 }
 
 function updateFlamegraphView() {
-  const selectedData = selectFlamegraphData();
   const selectedThreadId = currentThreadFilter !== 'all' ? parseInt(currentThreadFilter, 10) : null;
-  const filteredData = selectedThreadId !== null ? filterDataByThread(selectedData, selectedThreadId) : selectedData;
-  const tooltip = createPythonTooltip(filteredData);
-  const chart = createFlamegraph(tooltip, filteredData.value, filteredData);
-  renderFlamegraph(chart, filteredData);
+  const selectedData = selectFlamegraphData(selectedThreadId);
+  const tooltip = createPythonTooltip(selectedData);
+  const chart = createFlamegraph(tooltip, selectedData.value, selectedData);
+  renderFlamegraph(chart, selectedData);
   populateThreadStats(selectedData, selectedThreadId);
 }
 
@@ -937,7 +946,9 @@ function formatDuration(seconds) {
 
 function populateProfileSummary(data) {
   const stats = data.stats || {};
-  const totalSamples = stats.total_samples || data.value || 0;
+  const totalSamples = currentThreadFilter !== 'all'
+    ? (data.value ?? 0)
+    : (stats.total_samples ?? data.value ?? 0);
   const duration = stats.duration_sec || 0;
   const sampleRate = stats.sample_rate || (duration > 0 ? totalSamples / duration : 0);
   const errorRate = stats.error_rate || 0;
@@ -1209,7 +1220,7 @@ function initThreadFilter(data) {
   const threadFilter = document.getElementById('thread-filter');
   const threadSection = document.getElementById('thread-section');
 
-  if (!threadFilter || !data.threads) return;
+  if (!threadFilter || !data.threads || data.stats?.is_differential) return;
 
   threadFilter.innerHTML = '<option value="all">All Threads</option>';
 
@@ -1238,11 +1249,23 @@ function filterByThread() {
 
 function filterDataByThread(data, threadId) {
   function filterNode(node) {
-    if (!node.threads || !node.threads.includes(threadId)) {
+    const threadValues = node.thread_values?.[threadId];
+    if (!threadValues) {
       return null;
     }
 
-    const filteredNode = { ...node, children: [] };
+    const {
+      thread_values: _threadValues,
+      thread_opcodes: threadOpcodes,
+      ...sharedNode
+    } = node;
+    const filteredNode = {
+      ...sharedNode,
+      value: threadValues[0],
+      self: threadValues[1],
+      opcodes: threadOpcodes?.[threadId] ?? {},
+      children: []
+    };
 
     if (node.children && Array.isArray(node.children)) {
       filteredNode.children = node.children
@@ -1253,25 +1276,7 @@ function filterDataByThread(data, threadId) {
     return filteredNode;
   }
 
-  function recalculateValue(node) {
-    if (!node.children || node.children.length === 0) {
-      return node.value || 0;
-    }
-    const childrenValue = node.children.reduce((sum, child) => sum + recalculateValue(child), 0);
-    node.value = Math.max(node.value || 0, childrenValue);
-    return node.value;
-  }
-
-  const filteredRoot = { ...data, children: [] };
-
-  if (data.children && Array.isArray(data.children)) {
-    filteredRoot.children = data.children
-      .map(child => filterNode(child))
-      .filter(child => child !== null);
-  }
-
-  recalculateValue(filteredRoot);
-  return filteredRoot;
+  return filterNode(data);
 }
 
 // ============================================================================

Lib/profiling/sampling/stack_collector.py

@@ -71,7 +71,13 @@ class FlamegraphCollector(StackTraceCollector):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
         self.stats = {}
-        self._root = {"samples": 0, "children": {}, "threads": set()}
+        self._root = {
+            "samples": 0,
+            "children": {},
+            "threads": set(),
+            "thread_samples": collections.Counter(),
+            "thread_self": collections.Counter(),
+        }
         self._total_samples = 0
         self._sample_count = 0  # Track actual number of samples (not thread traces)
         self._func_intern = {}
@@ -220,7 +226,18 @@ def convert_children(children, min_samples, path_info):
             out = []
             for func, node in children.items():
                 samples = node["samples"]
-                if samples < min_samples:
+                significant_for_thread = any(
+                    thread_samples >= max(
+                        1,
+                        int(
+                            self._root["thread_samples"][thread_id]
+                            * 0.001
+                        ),
+                    )
+                    for thread_id, thread_samples
+                    in node["thread_samples"].items()
+                )
+                if samples < min_samples and not significant_for_thread:
                     continue
 
                 # Intern all string components for maximum efficiency
@@ -243,6 +260,15 @@ def convert_children(children, min_samples, path_info):
                     "lineno": func[1],
                     "funcname": funcname_idx,
                     "threads": sorted(list(node.get("threads", set()))),
+                    "thread_values": {
+                        thread_id: [
+                            samples,
+                            node["thread_self"].get(thread_id, 0),
+                        ]
+                        for thread_id, samples in sorted(
+                            node["thread_samples"].items()
+                        )
+                    },
                 }
 
                 source = self._get_source_lines(func)
@@ -255,6 +281,14 @@ def convert_children(children, min_samples, path_info):
                 opcodes = node.get("opcodes", {})
                 if opcodes:
                     child_entry["opcodes"] = dict(opcodes)
+                thread_opcodes = node.get("thread_opcodes")
+                if thread_opcodes:
+                    child_entry["thread_opcodes"] = {
+                        thread_id: dict(counts)
+                        for thread_id, counts in sorted(
+                            thread_opcodes.items()
+                        )
+                    }
 
                 # Recurse
                 child_entry["children"] = convert_children(
@@ -311,7 +345,25 @@ def convert_children(children, min_samples, path_info):
         opcode_mapping = get_opcode_mapping()
 
         # If we only have one root child, make it the root to avoid redundant level
-        if len(root_children) == 1:
+        root_thread_values = {
+            thread_id: [samples, 0]
+            for thread_id, samples in sorted(
+                self._root["thread_samples"].items()
+            )
+        }
+        sole_root_covers_profile = (
+            len(root_children) == 1
+            and root_children[0]["value"] == total_samples
+            and {
+                thread_id: values[0]
+                for thread_id, values
+                in root_children[0]["thread_values"].items()
+            } == {
+                thread_id: values[0]
+                for thread_id, values in root_thread_values.items()
+            }
+        )
+        if sole_root_covers_profile:
             main_child = root_children[0]
             # Update name and label to indicate it's the program root
             old_name = self._string_table.get_string(main_child["name"])
@@ -340,6 +392,7 @@ def convert_children(children, min_samples, path_info):
                 "per_thread_stats": per_thread_stats_with_pct
             },
             "threads": sorted(list(self._all_threads)),
+            "thread_values": root_thread_values,
             "strings": self._string_table.get_strings(),
             "opcode_mapping": opcode_mapping
         }
@@ -356,6 +409,7 @@ def process_frames(self, frames, thread_id, weight=1):
         """
         # Reverse to root->leaf order for tree building
         self._root["samples"] += weight
+        self._root["thread_samples"][thread_id] += weight
         self._total_samples += weight
         self._root["threads"].add(thread_id)
         self._all_threads.add(thread_id)
@@ -368,18 +422,32 @@ def process_frames(self, frames, thread_id, weight=1):
 
             node = current["children"].get(func)
             if node is None:
-                node = {"samples": 0, "children": {}, "threads": set(), "opcodes": collections.Counter(), "self": 0}
+                node = {
+                    "samples": 0,
+                    "children": {},
+                    "threads": set(),
+                    "thread_samples": collections.Counter(),
+                    "thread_self": collections.Counter(),
+                    "opcodes": collections.Counter(),
+                    "self": 0,
+                }
                 current["children"][func] = node
             node["samples"] += weight
+            node["thread_samples"][thread_id] += weight
             node["threads"].add(thread_id)
 
             if opcode is not None:
                 node["opcodes"][opcode] += weight
+                thread_opcodes = node.setdefault("thread_opcodes", {})
+                thread_opcodes.setdefault(
+                    thread_id, collections.Counter()
+                )[opcode] += weight
 
             current = node
 
         if current is not self._root:
             current["self"] += weight
+            current["thread_self"][thread_id] += weight
 
     def _get_source_lines(self, func):
         filename, lineno, _ = func