Windows: fetch oneMKL through vcpkg manifest mode (fixes setup on VS-bundled vcpkg)

.github/actions/setup-randblas-deps-windows/setup.ps1

@@ -110,6 +110,12 @@ if (-not $VcpkgExecutable) {
     if ($vcpkgCommand) {
         $vcpkgCandidates += $vcpkgCommand.Source
     }
+    if ($env:VSINSTALLDIR) {
+        # Visual Studio 2022 17.6+ bundles vcpkg with the C++ workload; a
+        # developer prompt exports VSINSTALLDIR but does not always put
+        # vcpkg.exe on PATH.
+        $vcpkgCandidates += Join-Path $env:VSINSTALLDIR "VC\vcpkg\vcpkg.exe"
+    }
     $VcpkgExecutable = $vcpkgCandidates |
         Where-Object { Test-Path -LiteralPath $_ } |
         Select-Object -First 1
@@ -130,11 +136,44 @@ $mklLibraries = @(
 )
 
 if (-not (Test-Path -LiteralPath $mklLibraries[0])) {
-    Invoke-Checked -Program $VcpkgExecutable -Arguments @(
-        "install",
-        "intel-mkl:x64-windows",
-        "--x-install-root=$vcpkgInstall"
-    )
+    # Manifest mode is the only mode every vcpkg distribution supports: the
+    # copy bundled with Visual Studio has no classic-mode instance, so
+    # `vcpkg install intel-mkl:x64-windows` fails there outright. Generate a
+    # minimal manifest and point every scratch tree at DependencyRoot -- the
+    # bundled vcpkg lives under Program Files, where its default scratch
+    # locations are not writable. The bundled vcpkg additionally requires
+    # builtin-baseline; the pin below is vcpkg release 2026.07.29
+    # (intel-mkl 2025.2.0), which also makes the oneMKL version independent
+    # of the vcpkg copy's age.
+    $vcpkgScratch = Join-Path $DependencyRoot "vcpkg-scratch"
+    $manifestDir = Join-Path $vcpkgScratch "manifest"
+    New-Item -ItemType Directory -Force -Path $manifestDir | Out-Null
+    Set-Content -Path (Join-Path $manifestDir "vcpkg.json") -Encoding ascii -Value @(
+        '{',
+        '  "name": "randblas-windows-deps",',
+        '  "version-string": "1",',
+        '  "builtin-baseline": "9e593bb18ea69cc5095e012465dcd675a822ed0d",',
+        '  "dependencies": [ "intel-mkl" ]',
+        '}')
+    Push-Location $manifestDir
+    try {
+        Invoke-Checked -Program $VcpkgExecutable -Arguments @(
+            "install",
+            "--triplet", "x64-windows",
+            "--x-install-root=$vcpkgInstall",
+            "--downloads-root=$(Join-Path $vcpkgScratch 'downloads')",
+            "--x-buildtrees-root=$(Join-Path $vcpkgScratch 'buildtrees')",
+            "--x-packages-root=$(Join-Path $vcpkgScratch 'packages')"
+        )
+    }
+    finally {
+        Pop-Location
+    }
+    # buildtrees/packages hold gigabytes of extracted installer scratch; the
+    # installed prefix is self-contained. Keep downloads so a re-run (or a
+    # CI downloads cache) skips the oneMKL fetch.
+    Remove-Item -Recurse -Force -ErrorAction SilentlyContinue `
+        (Join-Path $vcpkgScratch "buildtrees"), (Join-Path $vcpkgScratch "packages")
 }
 foreach ($path in @($mklInclude, $mklBin) + $mklLibraries) {
     if (-not (Test-Path -LiteralPath $path)) {

.github/workflows/core.yml

@@ -280,3 +280,56 @@ jobs:
             -Task $task `
             -WorkRoot "$env:GITHUB_WORKSPACE/../RandBLAS-windows-ci-$workName" `
             -SanitizeAddress:$sanitizeAddress
+
+  # User-fidelity lane: a plain Visual Studio install has no standalone
+  # vcpkg -- only the manifest-only copy bundled with the C++ workload. A
+  # classic-mode `vcpkg install` fails there ("this vcpkg distribution does
+  # not have a classic mode instance") while staying green on CI runners,
+  # which ship a classic-capable C:\vcpkg. This job hides the runner's
+  # standalone vcpkg and provisions oneMKL through the bundled copy. The
+  # vcpkg-installed tree is deliberately NOT cached so every run exercises
+  # the manifest-mode fetch; only the installer download is cached.
+  windows-vs-bundled-vcpkg:
+    name: windows-msvc-mkl-ilp64-vs-bundled-vcpkg
+    runs-on: windows-2022
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: initialize MSVC
+        uses: ilammy/msvc-dev-cmd@v1
+        with:
+          arch: x64
+
+      - name: cache oneMKL installer downloads
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}\..\windows-deps-vsvcpkg\vcpkg-scratch\downloads
+          key: windows-vsvcpkg-mkl-downloads-1-${{ hashFiles('.github/actions/setup-randblas-deps-windows/setup.ps1') }}
+
+      - name: cache GoogleTest installation
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}\..\windows-deps-vsvcpkg\googletest-install
+          key: windows-vsvcpkg-googletest-1.17.0-1
+
+      - name: cache BLAS++ installation
+        uses: actions/cache@v4
+        with:
+          path: ${{ github.workspace }}\..\windows-deps-vsvcpkg\blaspp-install
+          key: windows-vsvcpkg-blaspp-windows-portability-ilp64-sequential-3-${{ hashFiles('.github/actions/setup-randblas-deps-windows/setup.ps1') }}
+
+      - name: run native Windows core validation
+        shell: pwsh
+        run: |
+          Remove-Item Env:VCPKG_INSTALLATION_ROOT -ErrorAction SilentlyContinue
+          Remove-Item Env:VCPKG_ROOT -ErrorAction SilentlyContinue
+          $bundledVcpkg = Join-Path $env:VSINSTALLDIR "VC\vcpkg\vcpkg.exe"
+          if (-not (Test-Path $bundledVcpkg)) {
+            throw "Runner image has no VS-bundled vcpkg at $bundledVcpkg; this lane needs another way to reproduce a manifest-only vcpkg."
+          }
+          & "$env:GITHUB_WORKSPACE/.github/scripts/windows/run-ci.ps1" `
+            -Task CoreSerial `
+            -WorkRoot "$env:GITHUB_WORKSPACE/../RandBLAS-windows-ci-vsvcpkg" `
+            -DependencyRoot "$env:GITHUB_WORKSPACE/../windows-deps-vsvcpkg" `
+            -SetupDependencies `
+            -VcpkgExecutable $bundledVcpkg

INSTALL.md

@@ -176,7 +176,8 @@ Install the following tools first:
 * Visual Studio 2022 or Build Tools with **Desktop development with C++**;
 * Git;
 * CMake 3.24 or later;
-* vcpkg.
+* vcpkg (the copy bundled with Visual Studio's C++ workload works; so does a
+  standalone clone).
 
 Create the workspace directories:
 
@@ -187,17 +188,47 @@ mkdir C:\randblas-work\build
 mkdir C:\randblas-work\install
 ```
 
-The following command assumes vcpkg is installed at `C:\vcpkg`. Adjust that
-path if necessary. Install the oneMKL port into a dedicated dependency prefix:
+Install the oneMKL port into a dedicated dependency prefix. The commands below
+use vcpkg's manifest mode, which every vcpkg distribution supports -- the copy
+bundled with Visual Studio has no classic-mode instance, so a plain
+`vcpkg install intel-mkl:x64-windows` fails there. First write a minimal
+manifest (the bundled vcpkg requires the `builtin-baseline` field; the pin
+below is vcpkg release 2026.07.29, whose intel-mkl port is 2025.2.0):
 
 ```bat
-C:\vcpkg\vcpkg.exe install intel-mkl:x64-windows ^
-  --x-install-root=C:\randblas-work\vcpkg-installed
+mkdir C:\randblas-work\vcpkg-manifest
+(
+echo {
+echo   "name": "randblas-windows-deps",
+echo   "version-string": "1",
+echo   "builtin-baseline": "9e593bb18ea69cc5095e012465dcd675a822ed0d",
+echo   "dependencies": [ "intel-mkl" ]
+echo }
+) > C:\randblas-work\vcpkg-manifest\vcpkg.json
+```
+
+Then install from the manifest directory. The command below assumes the
+Visual Studio bundled vcpkg, which a Native Tools prompt exposes under
+`%VSINSTALLDIR%VC\vcpkg`; substitute `C:\vcpkg\vcpkg.exe` (or wherever your
+copy lives) if you use a standalone clone. The scratch-directory flags keep
+vcpkg's working trees out of the read-only Visual Studio install location:
+
+```bat
+cd C:\randblas-work\vcpkg-manifest
+"%VSINSTALLDIR%VC\vcpkg\vcpkg.exe" install ^
+  --triplet x64-windows ^
+  --x-install-root=C:\randblas-work\vcpkg-installed ^
+  --downloads-root=C:\randblas-work\vcpkg-scratch\downloads ^
+  --x-buildtrees-root=C:\randblas-work\vcpkg-scratch\buildtrees ^
+  --x-packages-root=C:\randblas-work\vcpkg-scratch\packages
 
 set "MKLROOT=C:\randblas-work\vcpkg-installed\x64-windows"
 set "PATH=%MKLROOT%\bin;%PATH%"
 ```
 
+After the install succeeds, `C:\randblas-work\vcpkg-scratch` can be deleted;
+the installed prefix is self-contained.
+
 Build a shared, sequential, ILP64 BLAS++:
 
 ```bat