New command: `spack config change` (#41147)

Like `spack change` for specs in environments, this can e.g. replace `examplespec+debug` with `examplespec~debug` in a `require:` section.

Example behavior for a config like:

```
packages:
  foo:
    require:
    - spec: +debug
```

* `spack config change packages:foo:require:~debug` replaces `+debug` with `~debug`
* `spack config change packages:foo:require:@1.1` adds a requirement to the list
* `spack config change packages:bar:require:~debug` adds a requirement

3 files changed, 192 insertions, 1 deletions

diff --git a/lib/spack/spack/cmd/config.py b/lib/spack/spack/cmd/config.py
index 50987ea069..adfe286c37 100644
--- a/lib/spack/spack/cmd/config.py
+++ b/lib/spack/spack/cmd/config.py
@@ -76,6 +76,10 @@ def setup_parser(subparser):
     )
     add_parser.add_argument("-f", "--file", help="file from which to set all config values")
 
+    change_parser = sp.add_parser("change", help="swap variants etc. on specs in config")
+    change_parser.add_argument("path", help="colon-separated path to config section with specs")
+    change_parser.add_argument("--match-spec", help="only change constraints that match this")
+
     prefer_upstream_parser = sp.add_parser(
         "prefer-upstream", help="set package preferences from upstream"
     )
@@ -263,6 +267,94 @@ def _can_update_config_file(scope: spack.config.ConfigScope, cfg_file):
     return fs.can_write_to_dir(scope.path) and fs.can_access(cfg_file)
 
 
+def _config_change_requires_scope(path, spec, scope, match_spec=None):
+    """Return whether or not anything changed."""
+    require = spack.config.get(path, scope=scope)
+    if not require:
+        return False
+
+    changed = False
+
+    def override_cfg_spec(spec_str):
+        nonlocal changed
+
+        init_spec = spack.spec.Spec(spec_str)
+        # Overridden spec cannot be anonymous
+        init_spec.name = spec.name
+        if match_spec and not init_spec.satisfies(match_spec):
+            # If there is a match_spec, don't change constraints that
+            # don't match it
+            return spec_str
+        elif not init_spec.intersects(spec):
+            changed = True
+            return str(spack.spec.Spec.override(init_spec, spec))
+        else:
+            # Don't override things if they intersect, otherwise we'd
+            # be e.g. attaching +debug to every single version spec
+            return spec_str
+
+    if isinstance(require, str):
+        new_require = override_cfg_spec(require)
+    else:
+        new_require = []
+        for item in require:
+            if "one_of" in item:
+                item["one_of"] = [override_cfg_spec(x) for x in item["one_of"]]
+            elif "any_of" in item:
+                item["any_of"] = [override_cfg_spec(x) for x in item["any_of"]]
+            elif "spec" in item:
+                item["spec"] = override_cfg_spec(item["spec"])
+            new_require.append(item)
+
+    spack.config.set(path, new_require, scope=scope)
+    return changed
+
+
+def _config_change(config_path, match_spec_str=None):
+    all_components = spack.config.process_config_path(config_path)
+    key_components = all_components[:-1]
+    key_path = ":".join(key_components)
+
+    spec = spack.spec.Spec(syaml.syaml_str(all_components[-1]))
+
+    match_spec = None
+    if match_spec_str:
+        match_spec = spack.spec.Spec(match_spec_str)
+
+    if key_components[-1] == "require":
+        # Extract the package name from the config path, which allows
+        # args.spec to be anonymous if desired
+        pkg_name = key_components[1]
+        spec.name = pkg_name
+
+        changed = False
+        for scope in spack.config.writable_scope_names():
+            changed |= _config_change_requires_scope(key_path, spec, scope, match_spec=match_spec)
+
+        if not changed:
+            existing_requirements = spack.config.get(key_path)
+            if isinstance(existing_requirements, str):
+                raise spack.config.ConfigError(
+                    "'config change' needs to append a requirement,"
+                    " but existing require: config is not a list"
+                )
+
+            ideal_scope_to_modify = None
+            for scope in spack.config.writable_scope_names():
+                if spack.config.get(key_path, scope=scope):
+                    ideal_scope_to_modify = scope
+                    break
+
+            update_path = f"{key_path}:[{str(spec)}]"
+            spack.config.add(update_path, scope=ideal_scope_to_modify)
+    else:
+        raise ValueError("'config change' can currently only change 'require' sections")
+
+
+def config_change(args):
+    _config_change(args.path, args.match_spec)
+
+
 def config_update(args):
     # Read the configuration files
     spack.config.CONFIG.get_config(args.section, scope=args.scope)
@@ -490,5 +582,6 @@ def config(parser, args):
         "update": config_update,
         "revert": config_revert,
         "prefer-upstream": config_prefer_upstream,
+        "change": config_change,
     }
     action[args.config_command](args)
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index d13cc643a2..be6aeea7f0 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -950,7 +950,8 @@ def scopes() -> Dict[str, ConfigScope]:
 
 def writable_scopes() -> List[ConfigScope]:
     """
-    Return list of writable scopes
+    Return list of writable scopes. Higher-priority scopes come first in the
+    list.
     """
     return list(
         reversed(
diff --git a/lib/spack/spack/test/cmd/env.py b/lib/spack/spack/test/cmd/env.py
index aaf2b83e23..0908ae3be3 100644
--- a/lib/spack/spack/test/cmd/env.py
+++ b/lib/spack/spack/test/cmd/env.py
@@ -48,6 +48,7 @@ env = SpackCommand("env")
 install = SpackCommand("install")
 add = SpackCommand("add")
 change = SpackCommand("change")
+config = SpackCommand("config")
 remove = SpackCommand("remove")
 concretize = SpackCommand("concretize")
 stage = SpackCommand("stage")
@@ -869,6 +870,102 @@ spack:
     assert any(x.satisfies("mpileaks@2.2") for x in e._get_environment_specs())
 
 
+def test_config_change_existing(mutable_mock_env_path, tmp_path, mock_packages, mutable_config):
+    """Test ``config change`` with config in the ``spack.yaml`` as well as an
+    included file scope.
+    """
+
+    included_file = "included-packages.yaml"
+    included_path = tmp_path / included_file
+    with open(included_path, "w") as f:
+        f.write(
+            """\
+packages:
+  mpich:
+    require:
+    - spec: "@3.0.2"
+  libelf:
+    require: "@0.8.10"
+  bowtie:
+    require:
+    - one_of: ["@1.3.0", "@1.2.0"]
+"""
+        )
+
+    spack_yaml = tmp_path / ev.manifest_name
+    spack_yaml.write_text(
+        f"""\
+spack:
+  packages:
+    mpich:
+      require:
+      - spec: "+debug"
+  include:
+  - {os.path.join(".", included_file)}
+  specs: []
+"""
+    )
+
+    e = ev.Environment(tmp_path)
+    with e:
+        # List of requirements, flip a variant
+        config("change", "packages:mpich:require:~debug")
+        test_spec = spack.spec.Spec("mpich").concretized()
+        assert test_spec.satisfies("@3.0.2~debug")
+
+        # List of requirements, change the version (in a different scope)
+        config("change", "packages:mpich:require:@3.0.3")
+        test_spec = spack.spec.Spec("mpich").concretized()
+        assert test_spec.satisfies("@3.0.3")
+
+        # "require:" as a single string, also try specifying
+        # a spec string that requires enclosing in quotes as
+        # part of the config path
+        config("change", 'packages:libelf:require:"@0.8.12:"')
+        test_spec = spack.spec.Spec("libelf@0.8.12").concretized()
+        # No need for assert, if there wasn't a failure, we
+        # changed the requirement successfully.
+
+        # Use "--match-spec" to change one spec in a "one_of"
+        # list
+        config("change", "packages:bowtie:require:@1.2.2", "--match-spec", "@1.2.0")
+        spack.spec.Spec("bowtie@1.3.0").concretize()
+        spack.spec.Spec("bowtie@1.2.2").concretized()
+
+
+def test_config_change_new(mutable_mock_env_path, tmp_path, mock_packages, mutable_config):
+    spack_yaml = tmp_path / ev.manifest_name
+    spack_yaml.write_text(
+        """\
+spack:
+  specs: []
+"""
+    )
+
+    e = ev.Environment(tmp_path)
+    with e:
+        config("change", "packages:mpich:require:~debug")
+        with pytest.raises(spack.solver.asp.UnsatisfiableSpecError):
+            spack.spec.Spec("mpich+debug").concretized()
+        spack.spec.Spec("mpich~debug").concretized()
+
+    # Now check that we raise an error if we need to add a require: constraint
+    # when preexisting config manually specified it as a singular spec
+    spack_yaml.write_text(
+        """\
+spack:
+  specs: []
+  packages:
+    mpich:
+      require: "@3.0.3"
+"""
+    )
+    with e:
+        assert spack.spec.Spec("mpich").concretized().satisfies("@3.0.3")
+        with pytest.raises(spack.config.ConfigError, match="not a list"):
+            config("change", "packages:mpich:require:~debug")
+
+
 def test_env_with_included_config_file_url(tmpdir, mutable_empty_config, packages_file):
     """Test configuration inclusion of a file whose path is a URL before
     the environment is concretized."""