ci: Just emit sym graph on Windows (docc broken), install Swift on Linux (default docc broken), fix iOS

The Windows job was broken cause DocC doesn't work on Windows yet. We
work around this by just uploading a symbol graph and assembling the
documentation archive in the update-docs job. The Linux job was broken
cause DocC doesn't handle being installed as root (it tries to copy
across file attributes from its root-installed resource files and fails).
The iOS job was broken because it was looking in the wrong place for the
archive. The actual location changes per platform so I've updated it to
just use 'find' to locate the archive somewhere in the derived data path.

Author: stackotter

.github/actions/compile-docs/action.yml

@@ -23,11 +23,8 @@ runs:
       run: |
         set -ex
         mkdir "$TARGET.doccarchive" && \
-        # We use --disable-sandbox instead of --allow-writing-to-directory because
-        # Linux and Windows throw tantrums about not being able to write to tmp (even
-        # though when I try locally I face no issues...)
         swift package \
-          --disable-sandbox \
+          --allow-writing-to-directory . \
           generate-documentation \
           --target "$TARGET" \
           --disable-indexing \
@@ -55,11 +52,7 @@ runs:
         echo "$DEVICE_TYPE"
         echo "Building documentation for destination '$destination'"
         xcodebuild -skipMacroValidation -scheme "$TARGET" -destination "$destination" -derivedDataPath /tmp/data docbuild | xcbeautify --renderer github-actions
-        ls /tmp/data
-        ls /tmp/data/Build
-        ls /tmp/data/Build/Products
-        ls /tmp/data/Build/Products/Debug
-        cp -R "/tmp/data/Build/Products/Debug/$TARGET.doccarchive" "$TARGET.doccarchive"
+        cp -R $(find /tmp/data -name "$TARGET.doccarchive") "$TARGET.doccarchive"
       shell: bash
       env:
         TARGET: ${{ inputs.target }}

.github/workflows/build-test-and-docs.yml

@@ -176,14 +176,20 @@ jobs:
         PKG_CONFIG_PATH: ${{ github.workspace }}/vcpkg_installed/${{ steps.triplet.outputs.lowercase }}/lib/pkgconfig
       run: swift build --target SwiftCrossUI -v
 
+    # DocC doesn't work on Windows yet, so we just emit the symbol graphs and construct
+    # the final WinUIBackend documentation archive in the update-docs job.
+    # Related issue: https://github.com/swiftlang/swift-docc/pull/668
     - name: Build WinUIBackend
-      run: swift build --target WinUIBackend
+      run: |
+        swift build --target WinUIBackend -v \
+          -Xswiftc -emit-symbol-graph \
+          -Xswiftc -emit-symbol-graph-dir -Xswiftc symbol-graphs
 
-    - name: Compile WinUIBackend docs
-      uses: ./.github/actions/compile-docs
+    - name: Upload WinUIBackend symbol graph
+      uses: actions/upload-artifact@v4
       with:
-        target: WinUIBackend
-        upload: true
+        name: WinUIBackend.symbols.json
+        path: symbol-graphs/WinUIBackend.symbols.json
 
   linux:
     strategy:
@@ -192,6 +198,11 @@ jobs:
     runs-on: ${{ matrix.os }}
 
     steps:
+    - name: Install Swift
+      uses: SwiftyLab/setup-swift@latest
+      with:
+        swift-version: "6.1.0"
+
     - name: Swift version
       run: swift --version
 
@@ -224,9 +235,6 @@ jobs:
     - name: Test
       run: swift test --test-product swift-cross-uiPackageTests
 
-    - name: Probe
-      run: ls /usr/share/swift/usr/share/docc/render/
-
     - name: Compile GtkBackend docs
       if: ${{ matrix.os == 'ubuntu-24.04' }}
       uses: ./.github/actions/compile-docs
@@ -281,11 +289,6 @@ jobs:
       with:
         name: Gtk3Backend.doccarchive.tar.gz
 
-    - name: Download WinUIBackend.doccarchive
-      uses: actions/download-artifact@v4
-      with:
-        name: WinUIBackend.doccarchive.tar.gz
-
     - name: Extract AppKitBackend.doccarchive.tar.gz
       uses: a7ul/tar-action@v1.1.0
       with:
@@ -310,11 +313,24 @@ jobs:
         command: x
         files: ./Gtk3Backend.doccarchive.tar.gz
 
-    - name: Extract WinUIBackend.doccarchive.tar.gz
-      uses: a7ul/tar-action@v1.1.0
+    - name: Download WinUIBackend.symbols.json
+      uses: actions/download-artifact@v4
       with:
-        command: x
-        files: ./WinUIBackend.doccarchive.tar.gz
+        name: WinUIBackend.symbols.json
+
+    - name: Compile WinUIBackend documentation
+      run: |
+        mkdir WinUIBackend.docc
+        mkdir winui-symbol-graphs
+        mv WinUIBackend.symbols.json winui-symbol-graphs/
+        xcrun docc convert WinUIBackend.docc \
+          --additional-symbol-graph-dir winui-symbol-graphs \
+          --transform-for-static-hosting \
+          --hosting-base-path swift-cross-ui \
+          --output-path "WinUIBackend.doccarchive" \
+          --source-service github \
+          --source-service-base-url https://github.com/stackotter/swift-cross-ui/blob/main \
+          --checkout-path $(pwd)
 
     - name: Merge DocC archives
       run: |