add Nim caching to the CI

Author: narimiran

.github/workflows/ci.yml

@@ -13,6 +13,7 @@ on:
       - stable
       - testing
       - unstable
+      - cache-nim
   pull_request:
     paths-ignore: ['media/**', 'docs/**', '**/*.md']
     branches-ignore:
@@ -157,11 +158,47 @@ jobs:
           echo "ncpu=${ncpu}" >> $GITHUB_ENV
           echo "make_cmd=${make_cmd}" >> $GITHUB_ENV
 
+
+      - name: Get Nim commit hash
+        id: nim-hash
+        run: |
+          BRANCH="${{ matrix.branch }}"
+          HASH=$(curl -s "https://api.github.com/repos/nim-lang/Nim/branches/${{ matrix.branch }}" | jq -r .commit.sha)
+          echo "NIM_COMMIT_HASH=$HASH" >> $GITHUB_ENV
+          echo "nim_commit_hash=$HASH" >> $GITHUB_OUTPUT
+
+      - name: Restore Nim build from cache
+        id: nim-cache
+        uses: actions/cache@v4
+        with:
+          path: |
+            nim/bin
+            nim/config
+            nim/lib
+            nim/nim.nimble
+          key: nim-${{ matrix.branch }}-${{ steps.nim-hash.outputs.nim_commit_hash }}-${{ matrix.target.os }}-${{ matrix.target.cpu }}
+
       - name: Build Nim and Nimbus dependencies
+        if: steps.nim-cache.outputs.cache-hit != 'true'
         run: |
           ${make_cmd} -j ${ncpu} NIM_COMMIT=${{ matrix.branch }} ARCH_OVERRIDE=${PLATFORM} QUICK_AND_DIRTY_COMPILER=1 update
           ./env.sh nim --version
 
+      - name: Save Nim build to cache
+        if: steps.nim-cache.outputs.cache-hit != 'true'
+        uses: actions/cache@v4
+        with:
+          path: |
+            nim/bin
+            nim/config
+            nim/lib
+            nim/nim.nimble
+          key: nim-${{ matrix.branch }}-${{ steps.nim-hash.outputs.nim_commit_hash }}-${{ matrix.target.os }}-${{ matrix.target.cpu }}
+
+      - name: Add Nim bin to GITHUB_PATH
+        run: echo '${{ github.workspace }}/nim/bin' >> $GITHUB_PATH
+
+
       - name: Build binaries (with trace logging enabled)
         run: |
           ${make_cmd} -j ${ncpu} V=1 NIM_COMMIT=${{ matrix.branch }} LOG_LEVEL=TRACE NIMFLAGS="-u:release --opt:none ${NIMFLAGS}"