diff --git a/lib/spack/spack/ci/common.py b/lib/spack/spack/ci/common.py
index 3f61803a733..90ce3af8325 100644
--- a/lib/spack/spack/ci/common.py
+++ b/lib/spack/spack/ci/common.py
@@ -26,6 +26,7 @@
 import spack.environment as ev
 import spack.error
 import spack.mirrors.mirror
+import spack.schema
 import spack.spec
 import spack.util.spack_yaml as syaml
 import spack.util.url as url_util
@@ -608,7 +609,7 @@ def __apply_submapping(self, dest, spec, section):
                     if "build-job-remove" in match_attrs:
                         spack.config.remove_yaml(dest, attrs["build-job-remove"])
                     if "build-job" in match_attrs:
-                        spack.config.merge_yaml(dest, attrs["build-job"])
+                        spack.schema.merge_yaml(dest, attrs["build-job"])
                     break
             if matched and only_first:
                 break
@@ -679,7 +680,7 @@ def _apply_section(dest, src):
                     if do_remove:
                         dest = spack.config.remove_yaml(dest, src[remove_job_name])
                     if do_merge:
-                        dest = copy.copy(spack.config.merge_yaml(dest, src[merge_job_name]))
+                        dest = copy.copy(spack.schema.merge_yaml(dest, src[merge_job_name]))
 
                 if name == "build":
                     # Apply attributes to all build jobs
@@ -808,7 +809,7 @@ def job_query(job):
                             tty.warn(f"Response missing required keys: {missing_keys}")
 
                     if clean_config:
-                        job["attributes"] = spack.config.merge_yaml(
+                        job["attributes"] = spack.schema.merge_yaml(
                             job.get("attributes", {}), clean_config
                         )
 
diff --git a/lib/spack/spack/ci/gitlab.py b/lib/spack/spack/ci/gitlab.py
index 65cab9a887c..735b9a20fd6 100644
--- a/lib/spack/spack/ci/gitlab.py
+++ b/lib/spack/spack/ci/gitlab.py
@@ -15,6 +15,7 @@
 import spack.binary_distribution as bindist
 import spack.config as cfg
 import spack.mirrors.mirror
+import spack.schema
 import spack.spec
 import spack.util.spack_yaml as syaml
 
@@ -248,7 +249,7 @@ def main_script_replacements(cmd):
                 build_stamp = options.cdash_handler.build_stamp
                 job_vars["SPACK_CDASH_BUILD_STAMP"] = build_stamp
 
-            job_object["artifacts"] = cfg.merge_yaml(
+            job_object["artifacts"] = spack.schema.merge_yaml(
                 job_object.get("artifacts", {}),
                 {
                     "when": "always",
diff --git a/lib/spack/spack/cmd/config.py b/lib/spack/spack/cmd/config.py
index aef2d7a5412..e8f573e67dd 100644
--- a/lib/spack/spack/cmd/config.py
+++ b/lib/spack/spack/cmd/config.py
@@ -14,6 +14,7 @@
 import spack.config
 import spack.environment as ev
 import spack.error
+import spack.schema
 import spack.schema.env
 import spack.spec
 import spack.store
@@ -566,7 +567,7 @@ def config_prefer_upstream(args):
 
     # Simply write the config to the specified file.
     existing = spack.config.get("packages", scope=scope)
-    new = spack.config.merge_yaml(existing, pkgs)
+    new = spack.schema.merge_yaml(existing, pkgs)
     spack.config.set("packages", new, scope)
     config_file = spack.config.CONFIG.get_config_filename(scope, section)
 
diff --git a/lib/spack/spack/config.py b/lib/spack/spack/config.py
index 1cafc1f738a..cd29af98806 100644
--- a/lib/spack/spack/config.py
+++ b/lib/spack/spack/config.py
@@ -619,7 +619,7 @@ def _get_config_memoized(self, section: str, scope: Optional[str]) -> YamlConfig
             if changed:
                 self.format_updates[section].append(scope)
 
-            merged_section = merge_yaml(merged_section, data)
+            merged_section = spack.schema.merge_yaml(merged_section, data)
 
         # no config files -- empty config.
         if section not in merged_section:
@@ -680,7 +680,7 @@ def set(self, path: str, value: Any, scope: Optional[str] = None) -> None:
         while len(parts) > 1:
             key = parts.pop(0)
 
-            if _override(key):
+            if spack.schema.override(key):
                 new = type(data[key])()
                 del data[key]
             else:
@@ -693,7 +693,7 @@ def set(self, path: str, value: Any, scope: Optional[str] = None) -> None:
                 data[key] = new
             data = new
 
-        if _override(parts[0]):
+        if spack.schema.override(parts[0]):
             data.pop(parts[0], None)
 
         # update new value
@@ -894,7 +894,7 @@ def add_from_file(filename: str, scope: Optional[str] = None) -> None:
 
             value = data[section]
             existing = get(section, scope=scope)
-            new = merge_yaml(existing, value)
+            new = spack.schema.merge_yaml(existing, value)
 
             # We cannot call config.set directly (set is a type)
             CONFIG.set(section, new, scope)
@@ -946,7 +946,7 @@ def add(fullpath: str, scope: Optional[str] = None) -> None:
         value: List[str] = [value]  # type: ignore[no-redef]
 
     # merge value into existing
-    new = merge_yaml(existing, value)
+    new = spack.schema.merge_yaml(existing, value)
     CONFIG.set(path, new, scope)
 
 
@@ -1120,44 +1120,6 @@ def read_config_file(
         raise ConfigFileError(str(e)) from e
 
 
-def _override(string: str) -> bool:
-    """Test if a spack YAML string is an override.
-
-    See ``spack_yaml`` for details.  Keys in Spack YAML can end in `::`,
-    and if they do, their values completely replace lower-precedence
-    configs instead of merging into them.
-
-    """
-    return hasattr(string, "override") and string.override
-
-
-def _append(string: str) -> bool:
-    """Test if a spack YAML string is an override.
-
-    See ``spack_yaml`` for details.  Keys in Spack YAML can end in `+:`,
-    and if they do, their values append lower-precedence
-    configs.
-
-    str, str : concatenate strings.
-    [obj], [obj] : append lists.
-
-    """
-    return getattr(string, "append", False)
-
-
-def _prepend(string: str) -> bool:
-    """Test if a spack YAML string is an override.
-
-    See ``spack_yaml`` for details.  Keys in Spack YAML can end in `+:`,
-    and if they do, their values prepend lower-precedence
-    configs.
-
-    str, str : concatenate strings.
-    [obj], [obj] : prepend lists. (default behavior)
-    """
-    return getattr(string, "prepend", False)
-
-
 def _mark_internal(data, name):
     """Add a simple name mark to raw YAML/JSON data.
 
@@ -1260,7 +1222,7 @@ def they_are(t):
             unmerge = sk in dest
             old_dest_value = dest.pop(sk, None)
 
-            if unmerge and not _override(sk):
+            if unmerge and not spack.schema.override(sk):
                 dest[sk] = remove_yaml(old_dest_value, sv)
 
         return dest
@@ -1270,81 +1232,6 @@ def they_are(t):
     return dest
 
 
-def merge_yaml(dest, source, prepend=False, append=False):
-    """Merges source into dest; entries in source take precedence over dest.
-
-    This routine may modify dest and should be assigned to dest, in
-    case dest was None to begin with, e.g.:
-
-       dest = merge_yaml(dest, source)
-
-    In the result, elements from lists from ``source`` will appear before
-    elements of lists from ``dest``. Likewise, when iterating over keys
-    or items in merged ``OrderedDict`` objects, keys from ``source`` will
-    appear before keys from ``dest``.
-
-    Config file authors can optionally end any attribute in a dict
-    with `::` instead of `:`, and the key will override that of the
-    parent instead of merging.
-
-    `+:` will extend the default prepend merge strategy to include string concatenation
-    `-:` will change the merge strategy to append, it also includes string concatentation
-    """
-
-    def they_are(t):
-        return isinstance(dest, t) and isinstance(source, t)
-
-    # If source is None, overwrite with source.
-    if source is None:
-        return None
-
-    # Source list is prepended (for precedence)
-    if they_are(list):
-        if append:
-            # Make sure to copy ruamel comments
-            dest[:] = [x for x in dest if x not in source] + source
-        else:
-            # Make sure to copy ruamel comments
-            dest[:] = source + [x for x in dest if x not in source]
-        return dest
-
-    # Source dict is merged into dest.
-    elif they_are(dict):
-        # save dest keys to reinsert later -- this ensures that  source items
-        # come *before* dest in OrderdDicts
-        dest_keys = [dk for dk in dest.keys() if dk not in source]
-
-        for sk, sv in source.items():
-            # always remove the dest items. Python dicts do not overwrite
-            # keys on insert, so this ensures that source keys are copied
-            # into dest along with mark provenance (i.e., file/line info).
-            merge = sk in dest
-            old_dest_value = dest.pop(sk, None)
-
-            if merge and not _override(sk):
-                dest[sk] = merge_yaml(old_dest_value, sv, _prepend(sk), _append(sk))
-            else:
-                # if sk ended with ::, or if it's new, completely override
-                dest[sk] = copy.deepcopy(sv)
-
-        # reinsert dest keys so they are last in the result
-        for dk in dest_keys:
-            dest[dk] = dest.pop(dk)
-
-        return dest
-
-    elif they_are(str):
-        # Concatenate strings in prepend mode
-        if prepend:
-            return source + dest
-        elif append:
-            return dest + source
-
-    # If we reach here source and dest are either different types or are
-    # not both lists or dicts: replace with source.
-    return copy.copy(source)
-
-
 class ConfigPath:
     quoted_string = "(?:\"[^\"]+\")|(?:'[^']+')"
     unquoted_string = "[^:'\"]+"
diff --git a/lib/spack/spack/detection/common.py b/lib/spack/spack/detection/common.py
index 1b16aa6ccd4..3b78b1783f4 100644
--- a/lib/spack/spack/detection/common.py
+++ b/lib/spack/spack/detection/common.py
@@ -27,6 +27,7 @@
 import spack.config
 import spack.error
 import spack.operating_systems.windows_os as winOs
+import spack.schema
 import spack.spec
 import spack.util.environment
 import spack.util.spack_yaml
@@ -226,7 +227,7 @@ def update_configuration(
         pkg_to_cfg[package_name] = pkg_config
 
     pkgs_cfg = spack.config.get("packages", scope=scope)
-    pkgs_cfg = spack.config.merge_yaml(pkgs_cfg, pkg_to_cfg)
+    pkgs_cfg = spack.schema.merge_yaml(pkgs_cfg, pkg_to_cfg)
     spack.config.set("packages", pkgs_cfg, scope=scope)
 
     return all_new_specs
@@ -246,7 +247,7 @@ def set_virtuals_nonbuildable(virtuals: Set[str], scope: Optional[str] = None) -
     # Update the provided scope
     spack.config.set(
         "packages",
-        spack.config.merge_yaml(spack.config.get("packages", scope=scope), new_config),
+        spack.schema.merge_yaml(spack.config.get("packages", scope=scope), new_config),
         scope=scope,
     )
 
diff --git a/lib/spack/spack/modules/common.py b/lib/spack/spack/modules/common.py
index e62520a6c2e..8ec53013fe2 100644
--- a/lib/spack/spack/modules/common.py
+++ b/lib/spack/spack/modules/common.py
@@ -48,6 +48,7 @@
 import spack.error
 import spack.paths
 import spack.projections as proj
+import spack.schema
 import spack.schema.environment
 import spack.spec
 import spack.store
@@ -216,7 +217,7 @@ def root_path(name, module_set_name):
     roots = spack.config.get(f"modules:{module_set_name}:roots", {})
 
     # Merge config values into the defaults so we prefer configured values
-    roots = spack.config.merge_yaml(defaults, roots)
+    roots = spack.schema.merge_yaml(defaults, roots)
 
     path = roots.get(name, os.path.join(spack.paths.share_path, name))
     return spack.util.path.canonicalize_path(path)
@@ -624,10 +625,10 @@ def environment_modifications(self):
         """List of environment modifications to be processed."""
         # Modifications guessed by inspecting the spec prefix
         prefix_inspections = syaml.syaml_dict()
-        spack.config.merge_yaml(
+        spack.schema.merge_yaml(
             prefix_inspections, spack.config.get("modules:prefix_inspections", {})
         )
-        spack.config.merge_yaml(
+        spack.schema.merge_yaml(
             prefix_inspections,
             spack.config.get(f"modules:{self.conf.name}:prefix_inspections", {}),
         )
diff --git a/lib/spack/spack/schema/__init__.py b/lib/spack/spack/schema/__init__.py
index 8c04ebdaac4..29001c48ab7 100644
--- a/lib/spack/spack/schema/__init__.py
+++ b/lib/spack/spack/schema/__init__.py
@@ -3,6 +3,7 @@
 #
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 """This module contains jsonschema files for all of Spack's YAML formats."""
+import copy
 import typing
 import warnings
 
@@ -73,3 +74,116 @@ def _deprecated_properties(validator, deprecated, instance, schema):
 
 
 Validator = llnl.util.lang.Singleton(_make_validator)
+
+
+def _append(string: str) -> bool:
+    """Test if a spack YAML string is an append.
+
+    See ``spack_yaml`` for details.  Keys in Spack YAML can end in `+:`,
+    and if they do, their values append lower-precedence
+    configs.
+
+    str, str : concatenate strings.
+    [obj], [obj] : append lists.
+
+    """
+    return getattr(string, "append", False)
+
+
+def _prepend(string: str) -> bool:
+    """Test if a spack YAML string is an prepend.
+
+    See ``spack_yaml`` for details.  Keys in Spack YAML can end in `+:`,
+    and if they do, their values prepend lower-precedence
+    configs.
+
+    str, str : concatenate strings.
+    [obj], [obj] : prepend lists. (default behavior)
+    """
+    return getattr(string, "prepend", False)
+
+
+def override(string: str) -> bool:
+    """Test if a spack YAML string is an override.
+
+    See ``spack_yaml`` for details.  Keys in Spack YAML can end in `::`,
+    and if they do, their values completely replace lower-precedence
+    configs instead of merging into them.
+
+    """
+    return hasattr(string, "override") and string.override
+
+
+def merge_yaml(dest, source, prepend=False, append=False):
+    """Merges source into dest; entries in source take precedence over dest.
+
+    This routine may modify dest and should be assigned to dest, in
+    case dest was None to begin with, e.g.:
+
+       dest = merge_yaml(dest, source)
+
+    In the result, elements from lists from ``source`` will appear before
+    elements of lists from ``dest``. Likewise, when iterating over keys
+    or items in merged ``OrderedDict`` objects, keys from ``source`` will
+    appear before keys from ``dest``.
+
+    Config file authors can optionally end any attribute in a dict
+    with `::` instead of `:`, and the key will override that of the
+    parent instead of merging.
+
+    `+:` will extend the default prepend merge strategy to include string concatenation
+    `-:` will change the merge strategy to append, it also includes string concatentation
+    """
+
+    def they_are(t):
+        return isinstance(dest, t) and isinstance(source, t)
+
+    # If source is None, overwrite with source.
+    if source is None:
+        return None
+
+    # Source list is prepended (for precedence)
+    if they_are(list):
+        if append:
+            # Make sure to copy ruamel comments
+            dest[:] = [x for x in dest if x not in source] + source
+        else:
+            # Make sure to copy ruamel comments
+            dest[:] = source + [x for x in dest if x not in source]
+        return dest
+
+    # Source dict is merged into dest.
+    elif they_are(dict):
+        # save dest keys to reinsert later -- this ensures that  source items
+        # come *before* dest in OrderdDicts
+        dest_keys = [dk for dk in dest.keys() if dk not in source]
+
+        for sk, sv in source.items():
+            # always remove the dest items. Python dicts do not overwrite
+            # keys on insert, so this ensures that source keys are copied
+            # into dest along with mark provenance (i.e., file/line info).
+            merge = sk in dest
+            old_dest_value = dest.pop(sk, None)
+
+            if merge and not override(sk):
+                dest[sk] = merge_yaml(old_dest_value, sv, _prepend(sk), _append(sk))
+            else:
+                # if sk ended with ::, or if it's new, completely override
+                dest[sk] = copy.deepcopy(sv)
+
+        # reinsert dest keys so they are last in the result
+        for dk in dest_keys:
+            dest[dk] = dest.pop(dk)
+
+        return dest
+
+    elif they_are(str):
+        # Concatenate strings in prepend mode
+        if prepend:
+            return source + dest
+        elif append:
+            return dest + source
+
+    # If we reach here source and dest are either different types or are
+    # not both lists or dicts: replace with source.
+    return copy.copy(source)
diff --git a/lib/spack/spack/schema/config.py b/lib/spack/spack/schema/config.py
index 9f380da92b7..b42c1e27ffa 100644
--- a/lib/spack/spack/schema/config.py
+++ b/lib/spack/spack/schema/config.py
@@ -11,7 +11,7 @@
 
 from llnl.util.lang import union_dicts
 
-import spack.config
+import spack.schema
 import spack.schema.projections
 
 #: Properties for inclusion in other schemas
@@ -157,7 +157,7 @@ def update(data):
         # whether install_tree was updated or not
         # we merge the yaml to ensure we don't invalidate other projections
         update_data = data.get("install_tree", {})
-        update_data = spack.config.merge_yaml(update_data, projections_data)
+        update_data = spack.schema.merge_yaml(update_data, projections_data)
         data["install_tree"] = update_data
         changed = True
 
diff --git a/lib/spack/spack/test/config.py b/lib/spack/spack/test/config.py
index 52e1cc9e04a..31d86d66fc4 100644
--- a/lib/spack/spack/test/config.py
+++ b/lib/spack/spack/test/config.py
@@ -639,31 +639,6 @@ def test_read_config_override_list(mock_low_high_config, write_config_file):
     }
 
 
-def test_ordereddict_merge_order():
-    """ "Test that source keys come before dest keys in merge_yaml results."""
-    source = syaml.syaml_dict([("k1", "v1"), ("k2", "v2"), ("k3", "v3")])
-
-    dest = syaml.syaml_dict([("k4", "v4"), ("k3", "WRONG"), ("k5", "v5")])
-
-    result = spack.config.merge_yaml(dest, source)
-    assert "WRONG" not in result.values()
-
-    expected_keys = ["k1", "k2", "k3", "k4", "k5"]
-    expected_items = [("k1", "v1"), ("k2", "v2"), ("k3", "v3"), ("k4", "v4"), ("k5", "v5")]
-    assert expected_keys == list(result.keys())
-    assert expected_items == list(result.items())
-
-
-def test_list_merge_order():
-    """ "Test that source lists are prepended to dest."""
-    source = ["a", "b", "c"]
-    dest = ["d", "e", "f"]
-
-    result = spack.config.merge_yaml(dest, source)
-
-    assert ["a", "b", "c", "d", "e", "f"] == result
-
-
 def test_internal_config_update(mock_low_high_config, write_config_file):
     write_config_file("config", config_low, "low")
 
diff --git a/lib/spack/spack/test/schema.py b/lib/spack/spack/test/schema.py
index 509bfd331a6..12f2c57e019 100644
--- a/lib/spack/spack/test/schema.py
+++ b/lib/spack/spack/test/schema.py
@@ -11,6 +11,7 @@
 
 import spack.paths
 import spack.schema
+import spack.util.spack_yaml as syaml
 
 
 @pytest.fixture()
@@ -124,3 +125,28 @@ def test_deprecated_properties(module_suffixes_schema):
     data = {"tcl": {"all": {"suffixes": {"^python": "py"}}}}
     # The next validation doesn't raise anymore
     v.validate(data)
+
+
+def test_ordereddict_merge_order():
+    """ "Test that source keys come before dest keys in merge_yaml results."""
+    source = syaml.syaml_dict([("k1", "v1"), ("k2", "v2"), ("k3", "v3")])
+
+    dest = syaml.syaml_dict([("k4", "v4"), ("k3", "WRONG"), ("k5", "v5")])
+
+    result = spack.schema.merge_yaml(dest, source)
+    assert "WRONG" not in result.values()
+
+    expected_keys = ["k1", "k2", "k3", "k4", "k5"]
+    expected_items = [("k1", "v1"), ("k2", "v2"), ("k3", "v3"), ("k4", "v4"), ("k5", "v5")]
+    assert expected_keys == list(result.keys())
+    assert expected_items == list(result.items())
+
+
+def test_list_merge_order():
+    """ "Test that source lists are prepended to dest."""
+    source = ["a", "b", "c"]
+    dest = ["d", "e", "f"]
+
+    result = spack.schema.merge_yaml(dest, source)
+
+    assert ["a", "b", "c", "d", "e", "f"] == result