Add a "requires" directive, extend functionality of package requirements (#36286)

Add a "require" directive to packages, which functions exactly like
requirements specified in packages.yaml (uses the same fact-generation
logic); update both to allow making the requirement conditional.

* Packages may now use "require" to add constraints. This can be useful
  for something like "require(%gcc)" (where before we had to add a
  conflict for every compiler except gcc).
* Requirements (in packages.yaml or in a "require" directive) can be
  conditional on a spec, e.g. "require(%gcc, when=@1.0.0)" (version
  1.0.0 can only build with gcc).
* Requirements may include a message which clarifies why they are needed.
  The concretizer assigns a high priority to errors which generate these
  messages (in particular over errors for unsatisfied requirements that
  do not produce messages, but also over a number of more-generic
  errors).

6 files changed, 41 insertions, 26 deletions

diff --git a/var/spack/repos/builtin.mock/packages/requires_clang/package.py b/var/spack/repos/builtin.mock/packages/requires_clang/package.py
new file mode 100644
index 0000000000..9f1c2d0ba4
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/requires_clang/package.py
@@ -0,0 +1,18 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import *
+
+
+class RequiresClang(Package):
+    """Simple package with no dependencies"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/b-1.0.tar.gz"
+
+    version("1.0", md5="0123456789abcdef0123456789abcdef")
+    version("0.9", md5="abcd456789abcdef0123456789abcdef")
+
+    requires("%clang", msg="can only be compiled with Clang")
diff --git a/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py b/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py
new file mode 100644
index 0000000000..18f924e92f
--- /dev/null
+++ b/var/spack/repos/builtin.mock/packages/requires_clang_or_gcc/package.py
@@ -0,0 +1,18 @@
+# Copyright 2013-2023 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+from spack.package import *
+
+
+class RequiresClangOrGcc(Package):
+    """Simple package with no dependencies"""
+
+    homepage = "http://www.example.com"
+    url = "http://www.example.com/b-1.0.tar.gz"
+
+    version("1.0", md5="0123456789abcdef0123456789abcdef")
+    version("0.9", md5="abcd456789abcdef0123456789abcdef")
+
+    requires("%gcc", "%clang", policy="one_of")
diff --git a/var/spack/repos/builtin/packages/bucky/package.py b/var/spack/repos/builtin/packages/bucky/package.py
index 5bd0c9fdf6..601729e82e 100644
--- a/var/spack/repos/builtin/packages/bucky/package.py
+++ b/var/spack/repos/builtin/packages/bucky/package.py
@@ -18,13 +18,7 @@ class Bucky(MakefilePackage):
 
     version("1.4.4", sha256="1621fee0d42314d9aa45d0082b358d4531e7d1d1a0089c807c1b21fbdc4e4592")
 
-    # Compilation requires gcc
-    conflicts("%cce")
-    conflicts("%apple-clang")
-    conflicts("%nag")
-    conflicts("%pgi")
-    conflicts("%xl")
-    conflicts("%xl_r")
+    requires("%gcc", msg="bucky can only be compiled with GCC")
 
     build_directory = "src"
 
diff --git a/var/spack/repos/builtin/packages/dyninst/package.py b/var/spack/repos/builtin/packages/dyninst/package.py
index c977fcc408..4079212ecf 100644
--- a/var/spack/repos/builtin/packages/dyninst/package.py
+++ b/var/spack/repos/builtin/packages/dyninst/package.py
@@ -87,19 +87,11 @@ class Dyninst(CMakePackage):
     patch("v9.3.2-auto.patch", when="@9.3.2 %gcc@:4.7")
     patch("tribool.patch", when="@9.3.0:10.0.0 ^boost@1.69:")
 
+    requires("%gcc", msg="dyninst builds only with GCC")
+
     # No Mac support (including apple-clang)
     conflicts("platform=darwin", msg="macOS is not supported")
 
-    # We currently only build with gcc
-    conflicts("%clang")
-    conflicts("%arm")
-    conflicts("%cce")
-    conflicts("%fj")
-    conflicts("%intel")
-    conflicts("%pgi")
-    conflicts("%xl")
-    conflicts("%xl_r")
-
     # Version 11.0 requires a C++11-compliant ABI
     conflicts("%gcc@:5", when="@11.0.0:")
 
diff --git a/var/spack/repos/builtin/packages/ffte/package.py b/var/spack/repos/builtin/packages/ffte/package.py
index 8b5b36c788..ed6de99aa4 100644
--- a/var/spack/repos/builtin/packages/ffte/package.py
+++ b/var/spack/repos/builtin/packages/ffte/package.py
@@ -32,12 +32,7 @@ class Ffte(Package):
 
     depends_on("mpi", when="+mpi")
 
-    conflicts("%cce", when="+cuda", msg="Must use NVHPC compiler")
-    conflicts("%clang", when="+cuda", msg="Must use NVHPC compiler")
-    conflicts("%gcc", when="+cuda", msg="Must use NVHPC compiler")
-    conflicts("%llvm", when="+cuda", msg="Must use NVHPC compiler")
-    conflicts("%nag", when="+cuda", msg="Must use NVHPC compiler")
-    conflicts("%intel", when="+cuda", msg="Must use NVHPC compiler")
+    requires("%nvhpc", when="+cuda", msg="ffte+cuda must use NVHPC compiler")
 
     def edit(self, spec, prefix):
         "No make-file, must create one from scratch."
diff --git a/var/spack/repos/builtin/packages/gcc/package.py b/var/spack/repos/builtin/packages/gcc/package.py
index 15bede82c0..259629d31e 100644
--- a/var/spack/repos/builtin/packages/gcc/package.py
+++ b/var/spack/repos/builtin/packages/gcc/package.py
@@ -273,9 +273,7 @@ class Gcc(AutotoolsPackage, GNUMirrorPackage):
         # See https://gcc.gnu.org/install/prerequisites.html#GDC-prerequisite
         with when("@12:"):
             # All versions starting 12 have to be built GCC:
-            for c in spack.compilers.supported_compilers():
-                if c != "gcc":
-                    conflicts("%{0}".format(c))
+            requires("%gcc")
 
             # And it has to be GCC older than the version we build:
             vv = ["11", "12.1.0", "12.2.0"]