build: modernize LLVM build and release workflow

.claude/commands/upgrade-llvm.md

@@ -0,0 +1,136 @@
+Upgrade LLVM to a new version. Accepts the target version as argument (e.g., `22.1.4`).
+
+This is the complete workflow for upgrading the LLVM prebuilt packages that clice depends on. Follow each step in order. Steps that involve CI should use polling (check every ~5 minutes) to wait for completion.
+
+## Step 1: Trigger LLVM Build
+
+Trigger the `build-llvm` workflow on GitHub Actions:
+
+```bash
+gh workflow run build-llvm.yml \
+  --field llvm_version="<VERSION>"
+```
+
+- Poll until all 14 matrix builds complete (~2-3 hours), note the workflow run ID
+
+## Step 2: Download Local Platform Artifact
+
+Download the artifact matching the development machine:
+
+```bash
+gh run view <RUN_ID>
+gh run download <RUN_ID> -n x64-linux-gnu-releasedbg.tar.xz -D .llvm-download
+mkdir -p .llvm
+tar -xf .llvm-download/x64-linux-gnu-releasedbg.tar.xz -C .llvm
+```
+
+Configure clice to build against it:
+
+```bash
+pixi run cmake-config RelWithDebInfo ON -- "-DLLVM_INSTALL_PATH=.llvm"
+pixi run cmake-build RelWithDebInfo
+```
+
+Compilation will likely fail — that's what Step 3 addresses.
+
+## Step 3: Adapt API Changes
+
+Fix LLVM API breaking changes based on compilation errors. Common categories:
+
+- **Header path changes**: e.g., `clang/Driver/Options.h` → `clang/Options/Options.h`
+- **Namespace migrations**: e.g., `clang::driver::options` → `clang::options`
+- **Type system changes**: e.g., ElaboratedType removal, NestedNameSpecifier pointer→value
+- **Function signature changes**: e.g., `createDiagnostics` parameter changes
+- **Type merges/splits**: e.g., DependentTemplateSpecializationType → TemplateSpecializationType
+
+Strategy:
+
+1. Fix header/namespace changes first (mechanical)
+2. Fix type system and signature changes (requires understanding semantics)
+3. Update test expectations (AST structure changes affect test output)
+4. Ensure `pixi run unit-test RelWithDebInfo` passes
+
+When a fix is not obvious, read the LLVM source code to understand the new API. If `../llvm-project` exists locally, use it. Otherwise, look up the upstream commit/PR on GitHub.
+
+## Step 4: Create PR
+
+```bash
+git checkout -b chore/upgrade-llvm-XX
+git add -A
+git commit -m "chore: upgrade LLVM to XX.Y.Z"
+git push -u origin chore/upgrade-llvm-XX
+gh pr create --title "chore: upgrade LLVM to XX.Y.Z" --body "..."
+```
+
+CI will fail at this point (manifest hashes are stale) — this is expected.
+
+## Step 5: Run Release LLVM Workflow
+
+Trigger `release-llvm` to build pruned packages:
+
+```bash
+gh workflow run release-llvm.yml \
+  --ref <BRANCH> \
+  --field source_run_id="<STEP1_RUN_ID>" \
+  --field llvm_version="<VERSION>"
+```
+
+This will: discover unused libs → create clice-llvm release → repackage with pruning. Poll until complete.
+
+## Step 6: Update Version
+
+Update the version string in `cmake/package.cmake`:
+
+```
+setup_llvm("<VERSION>")
+```
+
+Commit and push:
+
+```bash
+git add cmake/package.cmake
+git commit -m "chore: update LLVM to <VERSION>"
+git push
+```
+
+Poll CI until all platforms pass. CMake downloads the correct artifact automatically based on the version and platform — no manifest file needed.
+
+## Step 7: Write LLVM Changelog (REQUIRED)
+
+**Every LLVM upgrade MUST append to `docs/en/changelog/llvm-changelog.md`.**
+
+Add a new H2 section (e.g., `## LLVM 22 → 23`) documenting all breaking changes encountered. For each API change, record:
+
+- Change description
+- Upstream commit hash
+- PR number (link to `https://github.com/llvm/llvm-project/pull/<NUM>`)
+- Impact on clice
+
+To find upstream commits, search the LLVM git history between version tags:
+
+```bash
+# If ../llvm-project exists locally:
+cd ../llvm-project
+git log --oneline llvmorg-<OLD>..llvmorg-<NEW> -- clang/include/clang/AST/
+```
+
+If the LLVM source is not available locally, look up changes on GitHub by searching the LLVM repository commit history.
+
+Group changes by category (Type System, NNS, Driver/Frontend, Other) with a table per category. See the existing `LLVM 21 → 22` section as a template.
+
+## Step 8: Report to User
+
+Present a summary to the user and **wait for confirmation** before considering the upgrade complete. The summary should include:
+
+- All API changes that were adapted and how they were resolved
+- All test expectation changes (snapshot updates, assertion value changes) and why
+- Any unavoidable behavior changes from upstream LLVM (e.g., TypePrinter output differences, type sugar changes) that affect user-visible features like hover
+- The LLVM changelog that was written
+
+The user decides whether all changes are acceptable or if adjustments are needed. Do NOT push final changes or mark the work as done until the user confirms.
+
+## Notes
+
+- **Artifact size limit**: GitHub Release max 2GB per file. macOS LTO artifacts are largest, currently ~1.7GB with xz -9e.
+- **Pruning safety**: discover phase validates by deleting .a files one by one and rebuilding clice. clang-tidy modules can't be deleted due to force-link.
+- **Private headers**: clice depends on private Clang Sema headers (TreeTransform.h etc.), copied from source during `build-llvm.py`. Users must use our packaged LLVM.