Bootstrap most of Spack dependencies using environments (#34029)

This commit reworks the bootstrapping procedure to use Spack environments 
as much as possible.

The `spack.bootstrap` module has also been reorganized into a Python package. 
A distinction is made among "core" Spack dependencies (clingo, GnuPG, patchelf)
and other dependencies. For a number of reasons, explained in the `spack.bootstrap.core`
module docstring, "core" dependencies are bootstrapped with the current ad-hoc
method. 

All the other dependencies are instead bootstrapped using a Spack environment
that lives in a directory specific to the interpreter and the architecture being used. 

2 files changed, 35 insertions, 1 deletions

diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index b66f4cb1aa..5c90b1b5f3 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -408,7 +408,7 @@ _spack_bootstrap() {
 }
 
 _spack_bootstrap_now() {
-    SPACK_COMPREPLY="-h --help"
+    SPACK_COMPREPLY="-h --help --dev"
 }
 
 _spack_bootstrap_status() {
diff --git a/share/spack/templates/bootstrap/spack.yaml b/share/spack/templates/bootstrap/spack.yaml
new file mode 100644
index 0000000000..4573bb485e
--- /dev/null
+++ b/share/spack/templates/bootstrap/spack.yaml
@@ -0,0 +1,34 @@
+# This environment contains Spack non-core dependencies for the
+# following configuration
+#
+# Python spec: {{ python_spec }}
+# Python interpreter: {{ python_prefix }}
+# Architecture: {{ architecture }}
+#
+spack:
+  specs:
+{% for spec in environment_specs %}
+    - "{{ spec }}"
+{% endfor %}
+  view: {{ environment_path }}/view
+
+  config:
+    install_tree:
+      root: {{ store_path }}
+
+  packages:
+    python:
+      buildable: false
+      externals:
+        - spec: "{{ python_spec }}"
+          prefix: "{{ python_prefix }}"
+
+    py-typed-ast:
+      require: "+wheel"
+
+    py-platformdirs:
+      require: "+wheel"
+
+  concretizer:
+    reuse: false
+    unify: true