Windows: improve Git Bash detection

core/platform_compat.py

@@ -14,6 +14,7 @@ Design rules:
 from __future__ import annotations
 
 import os
+import ntpath
 import shutil
 import subprocess
 from pathlib import Path
@@ -134,11 +135,40 @@ _BASH_CACHE: Optional[str] = None
 _BASH_PROBED = False
 
 # Common Git-for-Windows install locations to probe when bash isn't on PATH.
-_WINDOWS_BASH_FALLBACKS = (
-    r"C:\Program Files\Git\bin\bash.exe",
-    r"C:\Program Files\Git\usr\bin\bash.exe",
-    r"C:\Program Files (x86)\Git\bin\bash.exe",
+_WINDOWS_BASH_ROOT_ENV_VARS = (
+    "ProgramFiles",
+    "ProgramW6432",
+    "ProgramFiles(x86)",
+    "LocalAppData",
 )
+_WINDOWS_BASH_DEFAULT_ROOTS = (
+    r"C:\Program Files\Git",
+    r"C:\Program Files (x86)\Git",
+)
+_WINDOWS_BASH_RELATIVE_PATHS = (
+    ("bin", "bash.exe"),
+    ("usr", "bin", "bash.exe"),
+)
+
+
+def _windows_bash_fallbacks() -> List[str]:
+    roots: List[str] = []
+    for env_name in _WINDOWS_BASH_ROOT_ENV_VARS:
+        base = os.environ.get(env_name)
+        if base:
+            roots.append(ntpath.join(base, "Git"))
+    roots.extend(_WINDOWS_BASH_DEFAULT_ROOTS)
+
+    paths: List[str] = []
+    seen = set()
+    for root in roots:
+        for rel in _WINDOWS_BASH_RELATIVE_PATHS:
+            path = ntpath.join(root, *rel)
+            key = path.lower()
+            if key not in seen:
+                seen.add(key)
+                paths.append(path)
+    return paths
 
 
 def find_bash() -> Optional[str]:
@@ -153,9 +183,9 @@ def find_bash() -> Optional[str]:
     if _BASH_PROBED:
         return _BASH_CACHE
     _BASH_PROBED = True
-    found = shutil.which("bash")
+    found = which_tool("bash")
     if not found and IS_WINDOWS:
-        for cand in _WINDOWS_BASH_FALLBACKS:
+        for cand in _windows_bash_fallbacks():
             if os.path.exists(cand):
                 found = cand
                 break

launch-windows.ps1

@@ -30,6 +30,26 @@ function Fail($msg) {
     exit 1
 }
 
+function Find-GitBash {
+    $cmd = Get-Command bash -ErrorAction SilentlyContinue
+    if ($cmd) { return $cmd.Source }
+
+    $roots = @()
+    foreach ($name in @("ProgramFiles", "ProgramW6432", "ProgramFiles(x86)", "LocalAppData")) {
+        $base = [Environment]::GetEnvironmentVariable($name)
+        if ($base) { $roots += (Join-Path $base "Git") }
+    }
+    $roots += @("C:\Program Files\Git", "C:\Program Files (x86)\Git")
+
+    foreach ($root in ($roots | Select-Object -Unique)) {
+        foreach ($relative in @("bin\bash.exe", "usr\bin\bash.exe")) {
+            $candidate = Join-Path $root $relative
+            if (Test-Path $candidate) { return $candidate }
+        }
+    }
+    return $null
+}
+
 # 1. Locate a Python interpreter (3.11+ required)
 Write-Step "Checking for Python"
 function Get-PythonVersionText($launcher, $launcherArgs) {
@@ -101,7 +121,7 @@ Write-Step "Running first-time setup"
 if ($LASTEXITCODE -ne 0) { Fail "setup.py failed." }
 
 # 5. Friendly note about Git Bash (full Cookbook / agent-shell parity)
-if (-not (Get-Command bash -ErrorAction SilentlyContinue)) {
+if (-not (Find-GitBash)) {
     Write-Host ""
     Write-Host "NOTE: Git Bash (bash.exe) was not found on PATH." -ForegroundColor Yellow
     Write-Host "      The core app works without it. For full Cookbook background" -ForegroundColor Yellow

tests/test_platform_compat.py

@@ -0,0 +1,37 @@
+"""Regression tests for cross-platform helper behavior."""
+
+from core import platform_compat
+
+
+def _reset_bash_cache(monkeypatch):
+    monkeypatch.setattr(platform_compat, "_BASH_CACHE", None)
+    monkeypatch.setattr(platform_compat, "_BASH_PROBED", False)
+
+
+def test_find_bash_tries_windows_exe_suffix(monkeypatch):
+    _reset_bash_cache(monkeypatch)
+    monkeypatch.setattr(platform_compat, "IS_WINDOWS", True)
+
+    expected = r"C:\Program Files\Git\bin\bash.exe"
+
+    def fake_which(name):
+        return expected if name == "bash.exe" else None
+
+    monkeypatch.setattr(platform_compat.shutil, "which", fake_which)
+    monkeypatch.setattr(platform_compat.os.path, "exists", lambda _path: False)
+
+    assert platform_compat.find_bash() == expected
+
+
+def test_find_bash_checks_local_app_data_git_install(monkeypatch):
+    _reset_bash_cache(monkeypatch)
+    monkeypatch.setattr(platform_compat, "IS_WINDOWS", True)
+    monkeypatch.setattr(platform_compat.shutil, "which", lambda _name: None)
+    for env_name in platform_compat._WINDOWS_BASH_ROOT_ENV_VARS:
+        monkeypatch.delenv(env_name, raising=False)
+    monkeypatch.setenv("LocalAppData", r"C:\Users\alice\AppData\Local")
+
+    expected = r"C:\Users\alice\AppData\Local\Git\bin\bash.exe"
+    monkeypatch.setattr(platform_compat.os.path, "exists", lambda path: path == expected)
+
+    assert platform_compat.find_bash() == expected