[build] Fix --skip-build-llvm so that its minimal targets, like tblgen, are still built

Author: finagolfin

utils/build-script

@@ -848,8 +848,11 @@ class BuildScriptInvocation(object):
         impl_product_classes = []
         if self.args.build_cmark:
             impl_product_classes.append(products.CMark)
-        if self.args.build_llvm:
-            impl_product_classes.append(products.LLVM)
+
+        # If --skip-build-llvm is passed in, LLVM cannot be completely disabled, as
+        # Swift still needs a few LLVM targets like tblgen to be built for it to be
+        # configured. Instead, handle this in build-script-impl for now.
+        impl_product_classes.append(products.LLVM)
         if self.args.build_libcxx:
             impl_product_classes.append(products.LibCXX)
         if self.args.build_libicu:

utils/build-script-impl

@@ -1157,10 +1157,14 @@ LIBDISPATCH_STATIC_SOURCE_DIR="${WORKSPACE}/swift-corelibs-libdispatch"
 LIBICU_SOURCE_DIR="${WORKSPACE}/icu"
 LIBCXX_SOURCE_DIR="${WORKSPACE}/llvm-project/libcxx"
 
+# We cannot currently apply the normal rules of skipping here for LLVM. Even if
+# we are skipping building LLVM, we still need to at least build a few tools
+# like tblgen that Swift relies on for building and testing. See the LLVM
+# configure rules.
+PRODUCTS=(llvm)
 [[ "${SKIP_BUILD_CMARK}" ]] || PRODUCTS+=(cmark)
 [[ "${SKIP_BUILD_LIBCXX}" ]] || PRODUCTS+=(libcxx)
 [[ "${SKIP_BUILD_LIBICU}" ]] || PRODUCTS+=(libicu)
-[[ "${SKIP_BUILD_LLVM}" ]] || PRODUCTS+=(llvm)
 [[ "${SKIP_BUILD_SWIFT}" ]] || PRODUCTS+=(swift)
 [[ "${SKIP_BUILD_LLDB}" ]] || PRODUCTS+=(lldb)
 [[ "${SKIP_BUILD_LIBDISPATCH}" ]] || PRODUCTS+=(libdispatch)
@@ -1550,7 +1554,7 @@ for host in "${ALL_HOSTS[@]}"; do
                 if [ "${BUILD_LLVM}" == "0" ] ; then
                     build_targets=(clean)
                 fi
-                if [ "${SKIP_BUILD}" ] ; then
+                if [[ "${SKIP_BUILD}" || "${SKIP_BUILD_LLVM}" ]] ; then
                     # We can't skip the build completely because the standalone
                     # build of Swift depend on these for building and testing.
                     build_targets=(llvm-tblgen clang-resource-headers intrinsics_gen clang-tablegen-targets)

validation-test/BuildSystem/skip_cmark_swift_llvm.test

@@ -20,7 +20,7 @@
 # SKIP-CMARK-CHECK: --- Installing swift ---
 
 # SKIP-LLVM-CHECK: cmake --build {{.*}}cmark-
-# SKIP-LLVM-CHECK-NOT: cmake --build {{.*}}llvm-
+# SKIP-LLVM-CHECK: cmake --build {{.*}}llvm-tblgen
 # SKIP-LLVM-CHECK: cmake --build {{.*}}swift-
 # SKIP-LLVM-CHECK: --- Installing cmark ---
 # SKIP-LLVM-CHECK-NOT: --- Installing llvm ---