Add automated Rust toolchain upgrade workflow

.github/check-rust-toolchain-upgrade.sh

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+#!/bin/bash
+set -euo pipefail
+
+# Check if rust-toolchain.toml exists
+if [ ! -f "rust-toolchain.toml" ]; then
+    echo "::error::rust-toolchain.toml not found"
+    exit 1
+fi
+
+# Read current channel from rust-toolchain.toml
+CURRENT_CHANNEL=$(grep '^channel = ' rust-toolchain.toml | head -1 | sed 's/channel = "\(.*\)"/\1/')
+CURRENT_DATE=$(echo "$CURRENT_CHANNEL" | sed 's/nightly-//')
+
+echo "Current toolchain: $CURRENT_CHANNEL"
+
+# Fetch latest nightly manifest
+MANIFEST_TOML_URL="https://static.rust-lang.org/dist/channel-rust-nightly.toml"
+MANIFEST_CONTENT=$(curl -sf "$MANIFEST_TOML_URL") || {
+    echo "::error::Failed to fetch manifest from $MANIFEST_TOML_URL"
+    exit 1
+}
+
+LATEST_DATE=$(echo "$MANIFEST_CONTENT" | grep '^date = ' | head -1 | sed 's/date = "\(.*\)"/\1/')
+
+if [ -z "$LATEST_DATE" ]; then
+    echo "::error::Could not extract date from manifest"
+    exit 1
+fi
+
+echo "Latest nightly date: $LATEST_DATE"
+
+# Convert dates to comparable format (remove dashes for numeric comparison)
+CURRENT_DATE_NUM=$(echo "$CURRENT_DATE" | tr -d '-')
+LATEST_DATE_NUM=$(echo "$LATEST_DATE" | tr -d '-')
+
+# Compare dates numerically
+if [ "$LATEST_DATE_NUM" -gt "$CURRENT_DATE_NUM" ]; then
+    echo "::notice::New nightly available: $LATEST_DATE (current: $CURRENT_DATE)"
+
+    # Get commit hash from the already fetched manifest
+    COMMIT_HASH=$(echo "$MANIFEST_CONTENT" | grep -A 50 '\[pkg.rust\]' | grep 'git-commit-hash = ' | head -1 | sed 's/git-commit-hash = "\(.*\)"/\1/')
+
+    if [ -z "$COMMIT_HASH" ]; then
+        echo "::error::Could not extract commit hash from manifest"
+        exit 1
+    fi
+
+    echo "New commit hash: $COMMIT_HASH"
+
+    # Write outputs for GitHub Actions
+    echo "SHOULD_UPGRADE=true" >> "${GITHUB_OUTPUT:-/dev/stdout}"
+    echo "NEW_DATE=$LATEST_DATE" >> "${GITHUB_OUTPUT:-/dev/stdout}"
+    echo "NEW_COMMIT_HASH=$COMMIT_HASH" >> "${GITHUB_OUTPUT:-/dev/stdout}"
+else
+    echo "::notice::No newer nightly available (current: $CURRENT_DATE, latest: $LATEST_DATE)"
+    echo "SHOULD_UPGRADE=false" >> "${GITHUB_OUTPUT:-/dev/stdout}"
+fi

.github/workflows/rust-toolchain-upgrade.yml

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+name: Rust Toolchain Upgrade
+
+on:
+  schedule:
+    # Run every day at 2 AM UTC
+    - cron: '0 2 * * *'
+  workflow_dispatch: # Allow manual triggering
+
+permissions:
+  contents: write
+  pull-requests: write
+
+jobs:
+  check-and-upgrade:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Check for new nightly
+        id: check-nightly
+        run: .github/check-rust-toolchain-upgrade.sh
+
+      - name: Update toolchain files
+        if: steps.check-nightly.outputs.SHOULD_UPGRADE == 'true'
+        run: |
+          NEW_DATE="${{ steps.check-nightly.outputs.NEW_DATE }}"
+          NEW_COMMIT_HASH="${{ steps.check-nightly.outputs.NEW_COMMIT_HASH }}"
+
+          # Update rust-toolchain.toml
+          sed -i "s/^channel = \"nightly-[0-9]\{4\}-[0-9]\{2\}-[0-9]\{2\}\"/channel = \"nightly-${NEW_DATE}\"/" rust-toolchain.toml
+          sed -i "s/^# commit_hash = [a-f0-9]\+/# commit_hash = ${NEW_COMMIT_HASH}/" rust-toolchain.toml
+
+          # Update REQUIRED_RUST_TOOLCHAIN in build.rs
+          sed -i "s/^channel = \"nightly-[0-9]\{4\}-[0-9]\{2\}-[0-9]\{2\}\"/channel = \"nightly-${NEW_DATE}\"/" crates/rustc_codegen_spirv/build.rs
+          sed -i "s/^# commit_hash = [a-f0-9]\+/# commit_hash = ${NEW_COMMIT_HASH}/" crates/rustc_codegen_spirv/build.rs
+
+      - name: Build project
+        if: steps.check-nightly.outputs.SHOULD_UPGRADE == 'true'
+        run: |
+          # The updated rust-toolchain.toml will cause cargo to download the required toolchain
+          cargo build
+
+      - name: Run tests
+        if: steps.check-nightly.outputs.SHOULD_UPGRADE == 'true'
+        run: |
+          cargo compiletest
+
+      - name: Create Pull Request
+        if: steps.check-nightly.outputs.SHOULD_UPGRADE == 'true'
+        uses: peter-evans/create-pull-request@v6
+        with:
+          token: ${{ secrets.GITHUB_TOKEN }}
+          commit-message: |
+            Upgrade Rust toolchain to nightly-${{ steps.check-nightly.outputs.NEW_DATE }}
+
+            Updates:
+            - rust-toolchain.toml: nightly-${{ steps.check-nightly.outputs.NEW_DATE }}
+            - commit hash: ${{ steps.check-nightly.outputs.NEW_COMMIT_HASH }}
+            - REQUIRED_RUST_TOOLCHAIN in build.rs
+          branch: rust-toolchain-upgrade
+          delete-branch: true
+          title: "Upgrade Rust toolchain to nightly-${{ steps.check-nightly.outputs.NEW_DATE }}"
+          body: |
+            This PR upgrades the Rust toolchain to the latest available nightly version.
+
+            ## Changes
+            - Updated `rust-toolchain.toml` to use `nightly-${{ steps.check-nightly.outputs.NEW_DATE }}`
+            - Updated commit hash to `${{ steps.check-nightly.outputs.NEW_COMMIT_HASH }}`
+            - Updated `REQUIRED_RUST_TOOLCHAIN` in `crates/rustc_codegen_spirv/build.rs`
+
+            ## Verification
+            - All required components are available
+            - Project builds successfully
+            - Tests pass
+
+            This PR was automatically generated by the [Rust toolchain upgrade workflow](https://github.com/Rust-GPU/rust-gpu/blob/main/.github/workflows/rust-toolchain-upgrade.yml).