`spack develop`: stage build artifacts in same root as non-dev builds (#41373)

Currently (outside of this PR) when you `spack develop` a path, this path is treated as the staging
directory (this means that for example all build artifacts are placed in the develop path).

This PR creates a separate staging directory for all `spack develop`ed builds. It looks like

```
# the stage root
/the-stage-root-for-all-spack-builds/
    spack-stage-<hash>
        # Spack packages inheriting CMakePackage put their build artifacts here
        spack-build-<hash>/
```

Unlike non-develop builds, there is no `spack-src` directory, `source_path` is the provided `dev_path`.
Instead, separately, in the `dev_path`, we have:

```
/dev/path/for/foo/
    build-{arch}-<hash> -> /the-stage-root-for-all-spack-builds/spack-stage-<hash>/
```

The main benefit of this is that build artifacts for out-of-source builds that are relative to
`Stage.path` are easily identified (and you can delete them with `spack clean`).

Other behavior added here:

- [x] A symlink is made from the `dev_path` to the stage directory. This symlink name incorporates
    spec details, so that multiple Spack environments that develop the same path will not conflict
    with one another

- [x] `spack cd` and `spack location` have added a `-c` shorthand for `--source-dir`

Spack builds can still change the develop path (in particular to keep track of applied patches), 
and for in-source builds, this doesn't change much (although logs would not be written into 
the develop path). Packages inheriting from `CMakePackage` should get this benefit
automatically though.

2 files changed, 8 insertions, 8 deletions

diff --git a/share/spack/spack-completion.bash b/share/spack/spack-completion.bash
index bdc2907d42..90d17c5f48 100755
--- a/share/spack/spack-completion.bash
+++ b/share/spack/spack-completion.bash
@@ -668,7 +668,7 @@ _spack_buildcache_rebuild_index() {
 _spack_cd() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -m --module-dir -r --spack-root -i --install-dir -p --package-dir -P --packages -s --stage-dir -S --stages --source-dir -b --build-dir -e --env --first"
+        SPACK_COMPREPLY="-h --help -m --module-dir -r --spack-root -i --install-dir -p --package-dir -P --packages -s --stage-dir -S --stages -c --source-dir -b --build-dir -e --env --first"
     else
         _all_packages
     fi
@@ -1347,7 +1347,7 @@ _spack_load() {
 _spack_location() {
     if $list_options
     then
-        SPACK_COMPREPLY="-h --help -m --module-dir -r --spack-root -i --install-dir -p --package-dir -P --packages -s --stage-dir -S --stages --source-dir -b --build-dir -e --env --first"
+        SPACK_COMPREPLY="-h --help -m --module-dir -r --spack-root -i --install-dir -p --package-dir -P --packages -s --stage-dir -S --stages -c --source-dir -b --build-dir -e --env --first"
     else
         _all_packages
     fi
diff --git a/share/spack/spack-completion.fish b/share/spack/spack-completion.fish
index 600213454b..84e1a4721e 100755
--- a/share/spack/spack-completion.fish
+++ b/share/spack/spack-completion.fish
@@ -880,7 +880,7 @@ complete -c spack -n '__fish_spack_using_command buildcache rebuild-index' -s k
 complete -c spack -n '__fish_spack_using_command buildcache rebuild-index' -s k -l keys -d 'if provided, key index will be updated as well as package index'
 
 # spack cd
-set -g __fish_spack_optspecs_spack_cd h/help m/module-dir r/spack-root i/install-dir p/package-dir P/packages s/stage-dir S/stages source-dir b/build-dir e/env= first
+set -g __fish_spack_optspecs_spack_cd h/help m/module-dir r/spack-root i/install-dir p/package-dir P/packages s/stage-dir S/stages c/source-dir b/build-dir e/env= first
 complete -c spack -n '__fish_spack_using_command_pos_remainder 0 cd' -f -k -a '(__fish_spack_specs)'
 complete -c spack -n '__fish_spack_using_command cd' -s h -l help -f -a help
 complete -c spack -n '__fish_spack_using_command cd' -s h -l help -d 'show this help message and exit'
@@ -898,8 +898,8 @@ complete -c spack -n '__fish_spack_using_command cd' -s s -l stage-dir -f -a sta
 complete -c spack -n '__fish_spack_using_command cd' -s s -l stage-dir -d 'stage directory for a spec'
 complete -c spack -n '__fish_spack_using_command cd' -s S -l stages -f -a stages
 complete -c spack -n '__fish_spack_using_command cd' -s S -l stages -d 'top level stage directory'
-complete -c spack -n '__fish_spack_using_command cd' -l source-dir -f -a source_dir
-complete -c spack -n '__fish_spack_using_command cd' -l source-dir -d 'source directory for a spec (requires it to be staged first)'
+complete -c spack -n '__fish_spack_using_command cd' -s c -l source-dir -f -a source_dir
+complete -c spack -n '__fish_spack_using_command cd' -s c -l source-dir -d 'source directory for a spec (requires it to be staged first)'
 complete -c spack -n '__fish_spack_using_command cd' -s b -l build-dir -f -a build_dir
 complete -c spack -n '__fish_spack_using_command cd' -s b -l build-dir -d 'build directory for a spec (requires it to be staged first)'
 complete -c spack -n '__fish_spack_using_command cd' -s e -l env -r -f -a location_env
@@ -2089,7 +2089,7 @@ complete -c spack -n '__fish_spack_using_command load' -l list -f -a list
 complete -c spack -n '__fish_spack_using_command load' -l list -d 'show loaded packages: same as `spack find --loaded`'
 
 # spack location
-set -g __fish_spack_optspecs_spack_location h/help m/module-dir r/spack-root i/install-dir p/package-dir P/packages s/stage-dir S/stages source-dir b/build-dir e/env= first
+set -g __fish_spack_optspecs_spack_location h/help m/module-dir r/spack-root i/install-dir p/package-dir P/packages s/stage-dir S/stages c/source-dir b/build-dir e/env= first
 complete -c spack -n '__fish_spack_using_command_pos_remainder 0 location' -f -k -a '(__fish_spack_specs)'
 complete -c spack -n '__fish_spack_using_command location' -s h -l help -f -a help
 complete -c spack -n '__fish_spack_using_command location' -s h -l help -d 'show this help message and exit'
@@ -2107,8 +2107,8 @@ complete -c spack -n '__fish_spack_using_command location' -s s -l stage-dir -f
 complete -c spack -n '__fish_spack_using_command location' -s s -l stage-dir -d 'stage directory for a spec'
 complete -c spack -n '__fish_spack_using_command location' -s S -l stages -f -a stages
 complete -c spack -n '__fish_spack_using_command location' -s S -l stages -d 'top level stage directory'
-complete -c spack -n '__fish_spack_using_command location' -l source-dir -f -a source_dir
-complete -c spack -n '__fish_spack_using_command location' -l source-dir -d 'source directory for a spec (requires it to be staged first)'
+complete -c spack -n '__fish_spack_using_command location' -s c -l source-dir -f -a source_dir
+complete -c spack -n '__fish_spack_using_command location' -s c -l source-dir -d 'source directory for a spec (requires it to be staged first)'
 complete -c spack -n '__fish_spack_using_command location' -s b -l build-dir -f -a build_dir
 complete -c spack -n '__fish_spack_using_command location' -s b -l build-dir -d 'build directory for a spec (requires it to be staged first)'
 complete -c spack -n '__fish_spack_using_command location' -s e -l env -r -f -a location_env