E2: Windows /cso build disables only C5105, and a failed MSVC compile is not reported as a missing toolchain

The Windows SDK's winbase.h raises C5105, which /W4 /WX promotes to error
C2220, so every MSVC build of the native /cso helper failed, and setup
mapped every probe failure to 'install Visual Studio 2022 Build Tools'.
Both compile lines add /wd5105 (only that diagnostic), and setup keeps the
probe's output: a probe that found MSVC but failed to compile reports
windows-msvc-compile with the compiler's first error. Not run on Windows:
the mapping test stubs powershell.exe; the ps1 assertion runs everywhere.

Co-authored-by: AlinValentin7 <AlinValentin7@users.noreply.github.com>

scripts/build-cso-windows.ps1

@@ -64,7 +64,10 @@ try {
         $output = Join-Path $temporary 'probe.exe'
         Set-Content -LiteralPath $source -Encoding Ascii -NoNewline -Value 'int main(void) { return 0; }'
         $object = Join-Path $temporary 'probe.obj'
-        & $compiler /nologo /std:c11 /W4 /WX /O2 /MT /GS /guard:cf /D_CRT_SECURE_NO_WARNINGS "/Fo$object" "/Fe$output" $source /link /DYNAMICBASE /NXCOMPAT /HIGHENTROPYVA
+        # /wd5105: the Windows SDK's own winbase.h raises C5105 ("macro expansion
+        # producing 'defined' has undefined behavior"), which /WX turns into
+        # error C2220 inside a system header (#3015). Only that diagnostic is off.
+        & $compiler /nologo /std:c11 /W4 /WX /wd5105 /O2 /MT /GS /guard:cf /D_CRT_SECURE_NO_WARNINGS "/Fo$object" "/Fe$output" $source /link /DYNAMICBASE /NXCOMPAT /HIGHENTROPYVA
         if ($LASTEXITCODE -ne 0) { throw "Native CSO Windows compiler probe failed ($LASTEXITCODE)." }
         if (-not (Test-Path -LiteralPath $output -PathType Leaf)) { throw 'Native CSO Windows compiler probe was not produced.' }
     } else {
@@ -78,7 +81,7 @@ try {
         foreach ($build in $builds) {
             $object = Join-Path $temporary $build.Object
             $forcedInclude = if ($build.Binding) { "/FI$binding" } else { @() }
-            & $compiler /nologo /std:c11 /W4 /WX /O2 /MT /GS /guard:cf /D_CRT_SECURE_NO_WARNINGS $forcedInclude "/Fo$object" "/Fe$($build.Output)" $build.Source /link /DYNAMICBASE /NXCOMPAT /HIGHENTROPYVA
+            & $compiler /nologo /std:c11 /W4 /WX /wd5105 /O2 /MT /GS /guard:cf /D_CRT_SECURE_NO_WARNINGS $forcedInclude "/Fo$object" "/Fe$($build.Output)" $build.Source /link /DYNAMICBASE /NXCOMPAT /HIGHENTROPYVA
             if ($LASTEXITCODE -ne 0) { throw "Native CSO Windows helper compilation failed ($LASTEXITCODE)." }
             if (-not (Test-Path -LiteralPath $build.Output -PathType Leaf)) { throw 'Native CSO Windows output was not produced.' }
         }

setup

@@ -1476,9 +1476,10 @@ _cso_unavailable() {
 # A successful probe is only a prerequisite check; any later source build failure
 # still aborts setup and therefore cannot be mistaken for a missing local tool.
 probe_cso_build_prerequisites() {
-  local _help _flag _platform _compiler _tmp _ps_script _repo_root _git_path
+  local _help _flag _platform _compiler _tmp _ps_script _repo_root _git_path _probe_out
   CSO_BUILD_AVAILABLE=1
   CSO_FAIL_REASON=""
+  CSO_PROBE_DETAIL=""
   if [ "${GSTACK_SETUP_SKIP_CSO_BUILD:-0}" = "1" ]; then
     _cso_unavailable "skipped-by-request"
     return 0
@@ -1505,9 +1506,16 @@ probe_cso_build_prerequisites() {
       _cso_unavailable "windows-git"
       return 0
     fi
-    if ! powershell.exe -NoProfile -NonInteractive -ExecutionPolicy Bypass \
-      -File "$_ps_script" -RepoRoot "$_repo_root" -GitExePath "$(cygpath -aw "$_git_path")" -CheckOnly >/dev/null 2>&1; then
-      _cso_unavailable "windows-msvc-toolchain"
+    # E2 (#3015): a probe that found MSVC but could not compile is not a
+    # missing toolchain; keep the probe's own first diagnostic for the summary.
+    if ! _probe_out="$(powershell.exe -NoProfile -NonInteractive -ExecutionPolicy Bypass \
+      -File "$_ps_script" -RepoRoot "$_repo_root" -GitExePath "$(cygpath -aw "$_git_path")" -CheckOnly 2>&1)"; then
+      case "$_probe_out" in
+        *"compiler probe failed"*|*"compiler probe was not produced"*)
+          _cso_unavailable "windows-msvc-compile"
+          CSO_PROBE_DETAIL="$(printf '%s\n' "$_probe_out" | grep -m1 -E 'error [A-Z]*[0-9]+|probe (failed|was not produced)' | tr -d '\r' | head -c 200)" ;;
+        *) _cso_unavailable "windows-msvc-toolchain" ;;
+      esac
     fi
     return 0
   fi
@@ -4194,6 +4202,7 @@ if [ "$CSO_BUILD_AVAILABLE" -eq 0 ]; then
     macos-codesign|macos-native-toolchain) _CSO_PREREQ="install the macOS compiler and codesign command-line tools" ;;
     windows-shell-toolchain) _CSO_PREREQ="run setup from Git Bash with Windows PowerShell available" ;;
     windows-msvc-toolchain) _CSO_PREREQ="install Visual Studio 2022 Build Tools with Desktop development with C++" ;;
+    windows-msvc-compile) _CSO_PREREQ="fix the MSVC compile error its toolchain probe reported (${CSO_PROBE_DETAIL:-see scripts/build-cso-windows.ps1 -CheckOnly}); Visual Studio is already installed" ;;
     windows-git) _CSO_PREREQ="install Git for Windows and run setup from its Git Bash" ;;
     unsupported-platform) _CSO_PREREQ="use a supported macOS, Linux, or Windows host" ;;
     skipped-by-request) _CSO_PREREQ="re-run without GSTACK_SETUP_SKIP_CSO_BUILD=1" ;;

test/setup-cso-windows-probe.test.ts

@@ -0,0 +1,69 @@
+import { afterEach, describe, expect, test } from 'bun:test';
+import * as fs from 'node:fs';
+import * as os from 'node:os';
+import * as path from 'node:path';
+import { runBashScript } from './helpers/bash-script';
+
+// E2 (#3015): the Windows /cso build compiles with /W4 /WX, and the Windows
+// SDK's winbase.h raises C5105, so every MSVC build failed; and setup reported
+// every probe failure as a missing Visual Studio toolchain. The probe and the
+// helper builds disable only C5105, and a probe that found MSVC but could not
+// compile gets its own reason with the compiler's first diagnostic. Runs the
+// real setup function on any OS with powershell.exe/cygpath stubbed.
+const ROOT = path.resolve(import.meta.dir, '..');
+const setup = fs.readFileSync(path.join(ROOT, 'setup'), 'utf8');
+const ps1 = fs.readFileSync(path.join(ROOT, 'scripts/build-cso-windows.ps1'), 'utf8');
+const fn = (name: string) => {
+  const start = setup.indexOf(`\n${name}() {`);
+  const end = setup.indexOf('\n}\n', start);
+  if (start < 0 || end < 0) throw new Error(`missing setup function ${name}`);
+  return setup.slice(start + 1, end + 3);
+};
+const summaryStart = setup.indexOf('  case "$CSO_FAIL_REASON" in');
+const summaryCase = setup.slice(summaryStart, setup.indexOf('\n  esac\n', summaryStart) + 8);
+
+const tmps: string[] = [];
+afterEach(() => { for (const t of tmps.splice(0)) fs.rmSync(t, { recursive: true, force: true }); });
+
+function probe(powershellOutput: string) {
+  const tmp = fs.mkdtempSync(path.join(os.tmpdir(), 'gstack-cso-win-'));
+  tmps.push(tmp);
+  fs.writeFileSync(path.join(tmp, 'powershell.exe'), `#!/bin/sh\ncat <<'OUT' >&2\n${powershellOutput}\nOUT\nexit 1\n`, { mode: 0o755 });
+  fs.writeFileSync(path.join(tmp, 'cygpath'), '#!/bin/sh\nshift; echo "$1"\n', { mode: 0o755 });
+  return runBashScript([
+    'IS_WINDOWS=1', `SOURCE_GSTACK_DIR="${ROOT}"`,
+    'bun_cmd() { echo "--no-compile-autoload-dotenv --no-compile-autoload-bunfig --no-compile-autoload-tsconfig --no-compile-autoload-package-json"; }',
+    fn('_cso_unavailable'), fn('probe_cso_build_prerequisites'),
+    'probe_cso_build_prerequisites', summaryCase,
+    'printf "reason=%s\\nprereq=%s\\n" "$CSO_FAIL_REASON" "$_CSO_PREREQ"',
+  ].join('\n'), { env: { ...process.env, PATH: `${tmp}:${process.env.PATH}` }, timeout: 30_000 });
+}
+
+describe('setup: Windows /cso build probe (E2)', () => {
+  test('both MSVC compile lines disable only C5105 and keep /W4 /WX', () => {
+    const lines = ps1.split('\n').filter(l => l.includes('& $compiler'));
+    expect(lines).toHaveLength(2);
+    for (const line of lines) expect(line).toContain('/W4 /WX /wd5105 ');
+  });
+});
+
+// The stubs are POSIX shell scripts named powershell.exe and cygpath, so the
+// reason mapping runs off Windows; the real probe needs MSVC (not verified here).
+describe.skipIf(process.platform === 'win32')('setup: Windows /cso probe failure mapping (E2)', () => {
+  test('a compile failure with MSVC present names the compiler error, not a missing toolchain', () => {
+    const r = probe([
+      "C:\\Program Files (x86)\\Windows Kits\\10\\include\\10.0.19041.0\\um\\winbase.h(9531): error C2220: the following warning is treated as an error",
+      'Native CSO Windows compiler probe failed (2).',
+    ].join('\n'));
+    expect(r.stdout).toContain('reason=windows-msvc-compile\n');
+    expect(r.stdout).toContain('prereq=fix the MSVC compile error its toolchain probe reported (');
+    expect(r.stdout).toContain('error C2220: the following warning is treated as an error');
+    expect(r.stdout).toContain('Visual Studio is already installed');
+  });
+
+  test('a missing Visual Studio toolchain keeps the install instruction', () => {
+    const r = probe('CSO Windows build requires Visual Studio 2022 Build Tools with the Desktop development with C++ workload.');
+    expect(r.stdout).toContain('reason=windows-msvc-toolchain\n');
+    expect(r.stdout).toContain('prereq=install Visual Studio 2022 Build Tools with Desktop development with C++\n');
+  });
+});