Sync pre-release CPython 3.15 branch from GitHub (2026-08-12)

Summary:
Imported python/cpython `3.15.0rc1+dev` from upstream rev [`1bcc1e4`](https://www.github.com/python/cpython/commit/1bcc1e467392c58c4ea59603e04d33f8670586cf) (committed 2026-08-12 00:15:34+00:00).

# Commit Info

- Base: (`3.15.0rc1+dev`) - [`2396815`](https://www.github.com/python/cpython/commit/2396815da3ed2993cac5f13c59f749b3057ae83f) (commit date: 2026-08-10 17:04:58+00:00)
- Imported: (`3.15.0rc1+dev`) - [`1bcc1e4`](https://www.github.com/python/cpython/commit/1bcc1e467392c58c4ea59603e04d33f8670586cf) (commit date: 2026-08-12 00:15:34+00:00)

# Noteworthy file changes

- Low-signal files (1 added) (NEWS.d, docs, .github)

Complete list of added/removed files: https://www.internalfb.com/intern/everpaste/?color=0&handle=GP5TPR4IkOWocdsEAHBCNuYUrNdebr0LAAAz

Differential Revision: D115680529

fbshipit-source-id: 85e093e25c6bfa301e4211c86e346aaca62183cd

Author: generatedunixname1734921407115435

.github/workflows/reusable-check-html-ids.yml

@@ -20,6 +20,13 @@ jobs:
         with:
           persist-credentials: false
           ref: ${{ github.event.pull_request.head.sha }}
+      - name: 'Downgrade Git'
+        # Temporarily downgrade to 2.43 until 2.55 is in the runner image,
+        # to avoid "fatal: shallow file has changed since we read it" bug.
+        # See https://github.com/python/cpython/issues/151365.
+        run: |
+          sudo apt-get install -y --allow-downgrades 'git=1:2.43.*' 'git-man=1:2.43.*'
+          git --version
       - name: 'Find merge base'
         id: merge-base
         run: |

.github/workflows/reusable-context.yml

@@ -94,6 +94,15 @@ jobs:
             || ''
           }}
 
+    - name: 'Downgrade Git'
+      # Temporarily downgrade to 2.43 until 2.55 is in the runner image,
+      # to avoid "fatal: shallow file has changed since we read it" bug.
+      # See https://github.com/python/cpython/issues/151365.
+      if: github.event_name == 'pull_request'
+      run: |
+        sudo apt-get install -y --allow-downgrades 'git=1:2.43.*' 'git-man=1:2.43.*'
+        git --version
+
     # Adapted from https://github.com/actions/checkout/issues/520#issuecomment-1167205721
     - name: Fetch commits to get branch diff
       if: github.event_name == 'pull_request'

.github/workflows/reusable-docs.yml

@@ -47,6 +47,14 @@ jobs:
             && github.event.pull_request.head.sha
             || ''
           }}
+    - name: 'Downgrade Git'
+      # Temporarily downgrade to 2.43 until 2.55 is in the runner image,
+      # to avoid "fatal: shallow file has changed since we read it" bug.
+      # See https://github.com/python/cpython/issues/151365.
+      if: github.event_name == 'pull_request'
+      run: |
+        sudo apt-get install -y --allow-downgrades 'git=1:2.43.*' 'git-man=1:2.43.*'
+        git --version
     # Adapted from https://github.com/actions/checkout/issues/520#issuecomment-1167205721
     - name: 'Fetch commits to get branch diff'
       if: github.event_name == 'pull_request'

Lib/profiling/sampling/_flamegraph_assets/flamegraph.js

@@ -99,6 +99,10 @@ function getDisplayName(moduleName, filename) {
   return filename;
 }
 
+function samplesToMilliseconds(samples, data) {
+  return (samples * data.stats.sample_interval_usec / 1000).toFixed(2);
+}
+
 function selectFlamegraphData(selectedThreadId = null) {
   let baseData = isShowingElided ? elidedFlamegraphData : normalData;
 
@@ -255,12 +259,12 @@ function setupLogos() {
 // Status Bar
 // ============================================================================
 
-function updateStatusBar(nodeData, rootValue) {
+function updateStatusBar(nodeData, rootValue, data) {
   const funcname = resolveString(nodeData.funcname) || resolveString(nodeData.name) || "--";
   const filename = resolveString(nodeData.filename) || "";
   const moduleName = resolveString(nodeData.module) || "";
   const lineno = nodeData.lineno;
-  const timeMs = (nodeData.value / 1000).toFixed(2);
+  const timeMs = samplesToMilliseconds(nodeData.value, data);
   const percent = rootValue > 0 ? ((nodeData.value / rootValue) * 100).toFixed(1) : "0.0";
 
   const brandEl = document.getElementById('status-brand');
@@ -322,9 +326,9 @@ function createPythonTooltip(data) {
         .style("opacity", 0);
     }
 
-    const timeMs = (d.data.value / 1000).toFixed(2);
+    const timeMs = samplesToMilliseconds(d.data.value, data);
     const selfSamples = d.data.self || 0;
-    const selfMs = (selfSamples / 1000).toFixed(2);
+    const selfMs = samplesToMilliseconds(selfSamples, data);
     const percentage = ((d.data.value / data.value) * 100).toFixed(2);
     const relativePercentage = Math.min(100, ((d.data.value / (zoomedNodeValue ?? data.value)) * 100)).toFixed(2);
     const calls = d.data.calls || 0;
@@ -408,9 +412,9 @@ function createPythonTooltip(data) {
     // Differential stats section
     let diffSection = "";
     if (d.data.diff !== undefined && d.data.baseline !== undefined) {
-      const baselineSelf = (d.data.baseline / 1000).toFixed(2);
-      const currentSelf = ((d.data.self_time || 0) / 1000).toFixed(2);
-      const diffMs = (d.data.diff / 1000).toFixed(2);
+      const baselineSelf = samplesToMilliseconds(d.data.baseline, data);
+      const currentSelf = samplesToMilliseconds(d.data.self_time || 0, data);
+      const diffMs = samplesToMilliseconds(d.data.diff, data);
       const diffPct = d.data.diff_pct;
       const sign = d.data.diff >= 0 ? "+" : "";
       const diffClass = d.data.diff > 0 ? "regression" : (d.data.diff < 0 ? "improvement" : "neutral");
@@ -508,7 +512,7 @@ function createPythonTooltip(data) {
       .style("opacity", 1);
 
     // Update status bar
-    updateStatusBar(d.data, data.value);
+    updateStatusBar(d.data, data.value, data);
   };
 
   pythonTooltip.hide = function () {

Lib/profiling/sampling/stack_collector.py

@@ -70,7 +70,7 @@ def export(self, filename):
 class FlamegraphCollector(StackTraceCollector):
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)
-        self.stats = {}
+        self.stats = {"sample_interval_usec": self.sample_interval_usec}
         self._root = {
             "samples": 0,
             "children": {},

Lib/test/test_profiling/test_sampling_profiler/test_collectors.py

@@ -505,6 +505,7 @@ def test_flamegraph_collector_basic(self):
         self.assertIn("func1 (file.py:10)", resolve_name(child, strings))
         self.assertEqual(child["value"], 1)
         self.assertEqual(child["self"], 1)  # leaf: all time is self
+        self.assertEqual(data["stats"]["sample_interval_usec"], 1000)
 
     def test_flamegraph_collector_export(self):
         """Test flamegraph HTML export functionality."""
@@ -513,7 +514,7 @@ def test_flamegraph_collector_export(self):
         )
         self.addCleanup(close_and_unlink, flamegraph_out)
 
-        collector = FlamegraphCollector(1000)
+        collector = FlamegraphCollector(10000)
 
         # Create some test data (use Interpreter/Thread objects like runtime)
         test_frames1 = [
@@ -569,6 +570,8 @@ def test_flamegraph_collector_export(self):
         self.assertIn('"name":', content)
         self.assertIn('"value":', content)
         self.assertIn('"children":', content)
+        self.assertIn('"sample_interval_usec": 10000', content)
+        self.assertIn("samples * data.stats.sample_interval_usec / 1000", content)
 
     def test_flamegraph_collector_empty_export_fails(self):
         """Test empty flamegraph export reports no output."""

Misc/NEWS.d/next/Tools-Demos/2026-07-19-00-00-00.gh-issue-154059.JiBcOM.rst

@@ -0,0 +1,2 @@
+Fix the time units in Tachyon flame graph tooltips by accounting for the
+sampling interval when converting samples to milliseconds.