[llvm] [llvm][release] Modernize the Windows release script (PR #228528)

[Alexandre Ganea via llvm-commits]

================
@@ -0,0 +1,2342 @@
+#!/usr/bin/env pwsh
+<#
+.SYNOPSIS
+    Script for building the LLVM installer on Windows,
+    used for the releases at https://github.com/llvm/llvm-project/releases
+
+.DESCRIPTION
+    Builds LLVM release packages for Windows (x64, arm64).
+    Performs a 2-stage build with a ThinLTO final stage and optional PGO.
+    Can bootstrap a fresh VM by installing all prerequisites.
+
+    By default, builds x64 using the local source tree and auto-detected
+    Python.  Use -DownloadSource to download a tagged release tarball
+    instead.
+
+    Build steps (in order):
+      1. libxml2   - Build libxml2, zlib, and zstd (inside stage 1 directory)
+      2. stage1    - Build the stage 1 bootstrap compiler with the host compiler
+      3. pgo       - PGO instrumented build + training + profile merge
+      4. stage2    - Build the stage 2 self-hosted compiler with stage 1 clang
+      5. package   - Create WiX MSI installer
+      6. tarball   - Generate full install tarball
+
+.PARAMETER Version
+    LLVM version string (e.g. "19.1.0").  If omitted, auto-detected from
+    the source tree.
+
+.PARAMETER x64
+    Build for x64 (64-bit).  This is the default if no architecture is specified.
+
+.PARAMETER arm64
+    Build for ARM64 (AArch64).
+
+.PARAMETER DownloadSource
+    Download and extract the tagged release source tarball from GitHub
+    instead of using the local source tree.  Requires -Version.
+
+.PARAMETER ForceMSVC
+    Force using MSVC (cl.exe) as the stage 0 host compiler instead of the
+    official LLVM release. Skips the LLVM release prerequisite.
+
+.PARAMETER FastBuild
+    Build only the stage 1 tools needed by stage 2 and skip the remaining
+    stage 1 targets, stage 1 tests, and PGO. Stage 2 tests still run.
+
+.PARAMETER InstallPrerequisites
+    Install build prerequisites (NetFx3, Visual Studio, official LLVM release,
+    CMake, Python and its psutil module, etc.)
+    before building.  When used with -arm64, also installs ARM64 Python for
+    LLDB.  Requests administrator elevation once for the entire prerequisite
+    installation when the current shell is not elevated.
+
+.PARAMETER Unattended
+    Never prompt for input.  Missing prerequisites cause the build to fail
+    unless -InstallPrerequisites is also specified.  An existing build
+    directory must be resumed with -StartAt or removed beforehand.  Run
+    from an elevated shell when using -InstallPrerequisites.
+
+.PARAMETER StartAt
+    Resume a previous build from a specific step.  Artifacts from earlier
+    steps must already exist on disk.  The step being restarted gets a
+    clean directory; earlier steps are skipped entirely.
+
+    Valid steps: libxml2, stage1, pgo, stage2, package, tarball
+
+    Pass an empty string (-StartAt "") or "?" (-StartAt "?") to display
+    the list of available steps and exit.
+
+.PARAMETER Help
+    Display this help message and exit.
+
+.EXAMPLE
+    .\build_llvm_release.ps1
+    Full x64 build using the local source tree.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -x64 -arm64
+    Build for both x64 and ARM64.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -Version 19.1.0 -DownloadSource
+    Download version 19.1.0 sources and build x64.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -InstallPrerequisites -x64
+    Install prerequisites, then do a full x64 build.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -InstallPrerequisites -x64 -arm64
+    Install prerequisites (including ARM64 Python), then build both architectures.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -Unattended -InstallPrerequisites
+    From an elevated shell, install prerequisites and build without prompts.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -x64 -StartAt stage2
+    Resume from stage 2 (reuses the stage 1 bootstrap compiler and PGO profile).
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -x64 -StartAt package
+    Resume at WiX MSI packaging, then regenerate the portable archive.
+
+.EXAMPLE
+    .\build_llvm_release.ps1 -StartAt ""
+    Display the list of available build steps and exit.
+
+.NOTES
+    Python is auto-detected from PATH for x64 builds.  For ARM64 builds,
+    the script probes standard install locations for ARM64 Python.  Use
+    -InstallPrerequisites to install it automatically.
+
+    Environment variables:
+      LLVM_NINJA_OVERRIDE  - Override the ninja binary and optionally provide
+                             extra flags.  The first token is the executable,
+                             remaining tokens are prepended to every ninja
+                             invocation.
+                             Example: LLVM_NINJA_OVERRIDE="myninja.exe --flag1 --flag2"
+#>
+
+param(
+    [string]$Version,
+    [switch]$x64,
+    [switch]$arm64,
+    [switch]$DownloadSource,
+    [switch]$ForceMSVC,
+    [switch]$FastBuild,
+    [switch]$InstallPrerequisites,
+    [switch]$Unattended,
+    [switch]$PrerequisitesOnly,  # Internal mode for the elevated installer.
+    [string]$StartAt,
+    [switch]$Help
+)
+
+#===============================================================================
+# PowerShell 7 self-relaunch
+#
+# This script requires PowerShell 7+ features (ternary operator, null-
+# coalescing, improved error handling, etc.).  If we detect we are running
+# under Windows PowerShell 5.x, we attempt to find or install PowerShell 7
+# and re-launch ourselves under it, forwarding all original arguments.
+#===============================================================================
+if ($PSVersionTable.PSVersion.Major -lt 7) {
----------------
aganea wrote:

I feel this is "standard" behavior as far as I am concerned. This is mostly to ease the user experience, if we start the `.ps1` directly on a clean image that doesn't have Powershell 7 installed. It would install it and re-start the script. We can fail here indeed, but the user would still need to install/upgrade Powershell manually, which I wanted to avoid.

https://github.com/llvm/llvm-project/pull/228528