fix code-signing on macOS (#15592)

* rebase

* move if statement location

* remove whitespace

* spec to self.spec

* switch statements as per review

* fix erronous indent

* add missing cmake arg

* minor placement fix for cmake args

* edit comment

* fix erronous return

* clarify conflicts with messages

* remove duplicate comment

* simplify logic

* macos wasn't a variant, fix that

* remove extra blank line

* address reviewer comments on spaces

var/spack/repos/builtin/packages/llvm/package.py

@@ -119,6 +119,8 @@ class Llvm(CMakePackage, CudaPackage):
         default=False,
         description="Build with OpenMP capable thread sanitizer",
     )
+    variant('code_signing', default=False,
+            description="Enable code-signing on macOS")
     variant("python", default=False, description="Install python bindings")
 
     extends("python", when="+python")
@@ -176,6 +178,20 @@ class Llvm(CMakePackage, CudaPackage):
     # MLIR exists in > 10.x
     conflicts("+mlir", when="@:9")
 
+    # code signing is only necessary on macOS",
+    conflicts('+code_signing', when='platform=linux')
+    conflicts('+code_signing', when='platform=bgq')
+    conflicts('+code_signing', when='platform=cray')
+
+    conflicts(
+        '+code_signing',
+        when='~lldb platform=darwin',
+        msg="code signing is only necessary for building the "
+            "in-tree debug server on macOS. Turning this variant "
+            "off enables a build of llvm with lldb that uses the "
+            "system debug server",
+    )
+
     # Github issue #4986
     patch("llvm_gcc7.patch", when="@4.0.0:4.0.1+lldb %gcc@7.0:")
     # Backport from llvm master + additional fix
@@ -192,30 +208,30 @@ class Llvm(CMakePackage, CudaPackage):
     # https://bugs.llvm.org/show_bug.cgi?id=39696
     patch("thread-p9.patch", when="@develop+libcxx")
 
-    @run_before("cmake")
+    @run_before('cmake')
-    def check_darwin_lldb_codesign_requirement(self):
+    def codesign_check(self):
-        if not self.spec.satisfies("+lldb platform=darwin"):
+        if self.spec.satisfies("+code_signing"):
-            return
+            codesign = which('codesign')
-        codesign = which("codesign")
+            mkdir('tmp')
-        mkdir("tmp")
+            llvm_check_file = join_path('tmp', 'llvm_check')
-        llvm_check_file = join_path("tmp", "llvm_check")
+            copy('/usr/bin/false', llvm_check_file)
-        copy("/usr/bin/false", llvm_check_file)
-
             try:
-            codesign("-f", "-s", "lldb_codesign", "--dryrun", llvm_check_file)
+                codesign('-f', '-s', 'lldb_codesign', '--dryrun',
+                         llvm_check_file)
 
             except ProcessError:
                 # Newer LLVM versions have a simple script that sets up
-            # automatically
+                # automatically when run with sudo priviliges
                 setup = Executable("./lldb/scripts/macos-setup-codesign.sh")
                 try:
                     setup()
                 except Exception:
                     raise RuntimeError(
-                    'The "lldb_codesign" identity must be available to build '
+                        'spack was unable to either find or set up'
-                    "LLVM with LLDB. See https://lldb.llvm.org/resources/"
+                        'code-signing on your system. Please refer to'
-                    "build.html#code-signing-on-macos for details on how to "
+                        'https://lldb.llvm.org/resources/build.html#'
-                    "create this identity."
+                        'code-signing-on-macos for details on how to'
+                        'create this identity.'
                     )
 
     def setup_build_environment(self, env):
@@ -355,6 +371,9 @@ def cmake_args(self):
             ):
                 cmake_args.append("-DCMAKE_BUILD_WITH_INSTALL_RPATH=1")
 
+        if self.spec.satisfies("~code_signing platform=darwin"):
+            cmake_args.append('-DLLDB_USE_SYSTEM_DEBUGSERVER=ON')
+
         # Semicolon seperated list of projects to enable
         cmake_args.append(
             "-DLLVM_ENABLE_PROJECTS:STRING={0}".format(";".join(projects))