From 5c7dda7e14ef05741d8dd1c4335883638836ee6b Mon Sep 17 00:00:00 2001
From: Massimiliano Culpo <massimiliano.culpo@gmail.com>
Date: Thu, 11 May 2023 22:29:17 +0200
Subject: [PATCH] Allow using -j to control the parallelism of concretization
 (#37608)

fixes #29464

This PR allows to use
```
$ spack concretize -j X
```
to set a cap on the parallelism of concretization from the command line
---
 lib/spack/spack/cmd/concretize.py          | 1 +
 lib/spack/spack/environment/environment.py | 5 ++++-
 share/spack/spack-completion.bash          | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/lib/spack/spack/cmd/concretize.py b/lib/spack/spack/cmd/concretize.py
index 14ff1ac1e2b..1b3ad66f936 100644
--- a/lib/spack/spack/cmd/concretize.py
+++ b/lib/spack/spack/cmd/concretize.py
@@ -29,6 +29,7 @@ def setup_parser(subparser):
     )
 
     spack.cmd.common.arguments.add_concretizer_args(subparser)
+    spack.cmd.common.arguments.add_common_arguments(subparser, ["jobs"])
 
 
 def concretize(parser, args):
diff --git a/lib/spack/spack/environment/environment.py b/lib/spack/spack/environment/environment.py
index 77748101024..263b30edabc 100644
--- a/lib/spack/spack/environment/environment.py
+++ b/lib/spack/spack/environment/environment.py
@@ -1475,7 +1475,10 @@ def _concretize_separately(self, tests=False):
 
         # Solve the environment in parallel on Linux
         start = time.time()
-        max_processes = min(len(arguments), 16)  # Number of specs  # Cap on 16 cores
+        max_processes = min(
+            len(arguments),  # Number of specs
+            spack.config.get("config:build_jobs"),  # Cap on build jobs
+        )
 
         # TODO: revisit this print as soon as darwin is parallel too
         msg = "Starting concretization"
diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index 0db940129a4..1644cffe6f2 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -734,7 +734,7 @@ _spack_compilers() {
 }
 
 _spack_concretize() {
-    SPACK_COMPREPLY="-h --help -f --force --test -q --quiet -U --fresh --reuse --reuse-deps"
+    SPACK_COMPREPLY="-h --help -f --force --test -q --quiet -U --fresh --reuse --reuse-deps -j --jobs"
 }
 
 _spack_config() {