diff --git a/lib/spack/spack/directory_layout.py b/lib/spack/spack/directory_layout.py
index 13643a8962b..8c2381cf653 100644
--- a/lib/spack/spack/directory_layout.py
+++ b/lib/spack/spack/directory_layout.py
@@ -25,7 +25,7 @@
 }
 
 
-def _check_concrete(spec):
+def _check_concrete(spec: "spack.spec.Spec") -> None:
     """If the spec is not concrete, raise a ValueError"""
     if not spec.concrete:
         raise ValueError("Specs passed to a DirectoryLayout must be concrete!")
@@ -51,7 +51,7 @@ def specs_from_metadata_dirs(root: str) -> List["spack.spec.Spec"]:
         spec = _get_spec(prefix)
 
         if spec:
-            spec.prefix = prefix
+            spec.set_prefix(prefix)
             specs.append(spec)
             continue
 
@@ -84,7 +84,7 @@ class DirectoryLayout:
 
     def __init__(
         self,
-        root,
+        root: str,
         *,
         projections: Optional[Dict[str, str]] = None,
         hash_length: Optional[int] = None,
@@ -120,17 +120,17 @@ def __init__(
         self.manifest_file_name = "install_manifest.json"
 
     @property
-    def hidden_file_regexes(self):
+    def hidden_file_regexes(self) -> Tuple[str]:
         return ("^{0}$".format(re.escape(self.metadata_dir)),)
 
-    def relative_path_for_spec(self, spec):
+    def relative_path_for_spec(self, spec: "spack.spec.Spec") -> str:
         _check_concrete(spec)
 
         projection = spack.projections.get_projection(self.projections, spec)
         path = spec.format_path(projection)
         return str(Path(path))
 
-    def write_spec(self, spec, path):
+    def write_spec(self, spec: "spack.spec.Spec", path: str) -> None:
         """Write a spec out to a file."""
         _check_concrete(spec)
         with open(path, "w", encoding="utf-8") as f:
@@ -138,7 +138,7 @@ def write_spec(self, spec, path):
             # the full provenance, so it's availabe if we want it later
             spec.to_json(f, hash=ht.dag_hash)
 
-    def write_host_environment(self, spec):
+    def write_host_environment(self, spec: "spack.spec.Spec") -> None:
         """The host environment is a json file with os, kernel, and spack
         versioning. We use it in the case that an analysis later needs to
         easily access this information.
@@ -148,7 +148,7 @@ def write_host_environment(self, spec):
         with open(env_file, "w", encoding="utf-8") as fd:
             sjson.dump(environ, fd)
 
-    def read_spec(self, path):
+    def read_spec(self, path: str) -> "spack.spec.Spec":
         """Read the contents of a file and parse them as a spec"""
         try:
             with open(path, encoding="utf-8") as f:
@@ -159,26 +159,28 @@ def read_spec(self, path):
                     # Too late for conversion; spec_file_path() already called.
                     spec = spack.spec.Spec.from_yaml(f)
                 else:
-                    raise SpecReadError(
-                        "Did not recognize spec file extension:" " {0}".format(extension)
-                    )
+                    raise SpecReadError(f"Did not recognize spec file extension: {extension}")
         except Exception as e:
             if spack.config.get("config:debug"):
                 raise
-            raise SpecReadError("Unable to read file: %s" % path, "Cause: " + str(e))
+            raise SpecReadError(f"Unable to read file: {path}", f"Cause: {e}")
 
         # Specs read from actual installations are always concrete
         spec._mark_concrete()
         return spec
 
-    def spec_file_path(self, spec):
+    def spec_file_path(self, spec: "spack.spec.Spec") -> str:
         """Gets full path to spec file"""
         _check_concrete(spec)
         yaml_path = os.path.join(self.metadata_path(spec), self._spec_file_name_yaml)
         json_path = os.path.join(self.metadata_path(spec), self.spec_file_name)
         return yaml_path if os.path.exists(yaml_path) else json_path
 
-    def deprecated_file_path(self, deprecated_spec, deprecator_spec=None):
+    def deprecated_file_path(
+        self,
+        deprecated_spec: "spack.spec.Spec",
+        deprecator_spec: Optional["spack.spec.Spec"] = None,
+    ) -> str:
         """Gets full path to spec file for deprecated spec
 
         If the deprecator_spec is provided, use that. Otherwise, assume
@@ -212,16 +214,16 @@ def deprecated_file_path(self, deprecated_spec, deprecator_spec=None):
 
         return yaml_path if os.path.exists(yaml_path) else json_path
 
-    def metadata_path(self, spec):
+    def metadata_path(self, spec: "spack.spec.Spec") -> str:
         return os.path.join(spec.prefix, self.metadata_dir)
 
-    def env_metadata_path(self, spec):
+    def env_metadata_path(self, spec: "spack.spec.Spec") -> str:
         return os.path.join(self.metadata_path(spec), "install_environment.json")
 
-    def build_packages_path(self, spec):
+    def build_packages_path(self, spec: "spack.spec.Spec") -> str:
         return os.path.join(self.metadata_path(spec), self.packages_dir)
 
-    def create_install_directory(self, spec):
+    def create_install_directory(self, spec: "spack.spec.Spec") -> None:
         _check_concrete(spec)
 
         # Create install directory with properly configured permissions
@@ -239,7 +241,7 @@ def create_install_directory(self, spec):
 
         self.write_spec(spec, self.spec_file_path(spec))
 
-    def ensure_installed(self, spec):
+    def ensure_installed(self, spec: "spack.spec.Spec") -> None:
         """
         Throws InconsistentInstallDirectoryError if:
         1. spec prefix does not exist
@@ -266,7 +268,7 @@ def ensure_installed(self, spec):
                 "Spec file in %s does not match hash!" % spec_file_path
             )
 
-    def path_for_spec(self, spec):
+    def path_for_spec(self, spec: "spack.spec.Spec") -> str:
         """Return absolute path from the root to a directory for the spec."""
         _check_concrete(spec)
 
@@ -277,23 +279,13 @@ def path_for_spec(self, spec):
         assert not path.startswith(self.root)
         return os.path.join(self.root, path)
 
-    def remove_install_directory(self, spec, deprecated=False):
+    def remove_install_directory(self, spec: "spack.spec.Spec", deprecated: bool = False) -> None:
         """Removes a prefix and any empty parent directories from the root.
         Raised RemoveFailedError if something goes wrong.
         """
         path = self.path_for_spec(spec)
         assert path.startswith(self.root)
 
-        # Windows readonly files cannot be removed by Python
-        # directly, change permissions before attempting to remove
-        if sys.platform == "win32":
-            kwargs = {
-                "ignore_errors": False,
-                "onerror": fs.readonly_file_handler(ignore_errors=False),
-            }
-        else:
-            kwargs = {}  # the default value for ignore_errors is false
-
         if deprecated:
             if os.path.exists(path):
                 try:
@@ -304,7 +296,16 @@ def remove_install_directory(self, spec, deprecated=False):
                     raise RemoveFailedError(spec, path, e) from e
         elif os.path.exists(path):
             try:
-                shutil.rmtree(path, **kwargs)
+                if sys.platform == "win32":
+                    # Windows readonly files cannot be removed by Python
+                    # directly, change permissions before attempting to remove
+                    shutil.rmtree(
+                        path,
+                        ignore_errors=False,
+                        onerror=fs.readonly_file_handler(ignore_errors=False),
+                    )
+                else:
+                    shutil.rmtree(path)
             except OSError as e:
                 raise RemoveFailedError(spec, path, e) from e
 
diff --git a/lib/spack/spack/filesystem_view.py b/lib/spack/spack/filesystem_view.py
index 2267928b6d5..855d7384e4a 100644
--- a/lib/spack/spack/filesystem_view.py
+++ b/lib/spack/spack/filesystem_view.py
@@ -10,7 +10,7 @@
 import stat
 import sys
 import tempfile
-from typing import Callable, Dict, Optional
+from typing import Callable, Dict, List, Optional
 
 from typing_extensions import Literal
 
@@ -78,7 +78,7 @@ def view_copy(
 
     # Order of this dict is somewhat irrelevant
     prefix_to_projection = {
-        s.prefix: view.get_projection_for_spec(s)
+        str(s.prefix): view.get_projection_for_spec(s)
         for s in spec.traverse(root=True, order="breadth")
         if not s.external
     }
@@ -185,7 +185,7 @@ def __init__(
     def link(self, src: str, dst: str, spec: Optional[spack.spec.Spec] = None) -> None:
         self._link(src, dst, self, spec)
 
-    def add_specs(self, *specs, **kwargs):
+    def add_specs(self, *specs: spack.spec.Spec, **kwargs) -> None:
         """
         Add given specs to view.
 
@@ -200,19 +200,19 @@ def add_specs(self, *specs, **kwargs):
         """
         raise NotImplementedError
 
-    def add_standalone(self, spec):
+    def add_standalone(self, spec: spack.spec.Spec) -> bool:
         """
         Add (link) a standalone package into this view.
         """
         raise NotImplementedError
 
-    def check_added(self, spec):
+    def check_added(self, spec: spack.spec.Spec) -> bool:
         """
         Check if the given concrete spec is active in this view.
         """
         raise NotImplementedError
 
-    def remove_specs(self, *specs, **kwargs):
+    def remove_specs(self, *specs: spack.spec.Spec, **kwargs) -> None:
         """
         Removes given specs from view.
 
@@ -231,25 +231,25 @@ def remove_specs(self, *specs, **kwargs):
         """
         raise NotImplementedError
 
-    def remove_standalone(self, spec):
+    def remove_standalone(self, spec: spack.spec.Spec) -> None:
         """
         Remove (unlink) a standalone package from this view.
         """
         raise NotImplementedError
 
-    def get_projection_for_spec(self, spec):
+    def get_projection_for_spec(self, spec: spack.spec.Spec) -> str:
         """
         Get the projection in this view for a spec.
         """
         raise NotImplementedError
 
-    def get_all_specs(self):
+    def get_all_specs(self) -> List[spack.spec.Spec]:
         """
         Get all specs currently active in this view.
         """
         raise NotImplementedError
 
-    def get_spec(self, spec):
+    def get_spec(self, spec: spack.spec.Spec) -> Optional[spack.spec.Spec]:
         """
         Return the actual spec linked in this view (i.e. do not look it up
         in the database by name).
@@ -263,7 +263,7 @@ def get_spec(self, spec):
         """
         raise NotImplementedError
 
-    def print_status(self, *specs, **kwargs):
+    def print_status(self, *specs: spack.spec.Spec, **kwargs) -> None:
         """
         Print a short summary about the given specs, detailing whether..
             * ..they are active in the view.
@@ -694,7 +694,7 @@ def _sanity_check_view_projection(self, specs):
                 raise ConflictingSpecsError(current_spec, conflicting_spec)
             seen[metadata_dir] = current_spec
 
-    def add_specs(self, *specs: spack.spec.Spec) -> None:
+    def add_specs(self, *specs, **kwargs) -> None:
         """Link a root-to-leaf topologically ordered list of specs into the view."""
         assert all((s.concrete for s in specs))
         if len(specs) == 0:
@@ -831,7 +831,7 @@ def get_projection_for_spec(self, spec):
 #####################
 # utility functions #
 #####################
-def get_spec_from_file(filename):
+def get_spec_from_file(filename) -> Optional[spack.spec.Spec]:
     try:
         with open(filename, "r", encoding="utf-8") as f:
             return spack.spec.Spec.from_yaml(f)
diff --git a/lib/spack/spack/spec.py b/lib/spack/spack/spec.py
index 4f4d154a14b..e5e624e8d08 100644
--- a/lib/spack/spack/spec.py
+++ b/lib/spack/spack/spec.py
@@ -2118,20 +2118,20 @@ def cshort_spec(self):
         return self.cformat(spec_format)
 
     @property
-    def prefix(self):
+    def prefix(self) -> spack.util.prefix.Prefix:
         if not self._concrete:
-            raise spack.error.SpecError("Spec is not concrete: " + str(self))
+            raise spack.error.SpecError(f"Spec is not concrete: {self}")
 
         if self._prefix is None:
-            upstream, record = spack.store.STORE.db.query_by_spec_hash(self.dag_hash())
+            _, record = spack.store.STORE.db.query_by_spec_hash(self.dag_hash())
             if record and record.path:
-                self.prefix = record.path
+                self.set_prefix(record.path)
             else:
-                self.prefix = spack.store.STORE.layout.path_for_spec(self)
+                self.set_prefix(spack.store.STORE.layout.path_for_spec(self))
+        assert self._prefix is not None
         return self._prefix
 
-    @prefix.setter
-    def prefix(self, value):
+    def set_prefix(self, value: str) -> None:
         self._prefix = spack.util.prefix.Prefix(llnl.path.convert_to_platform_path(value))
 
     def spec_hash(self, hash):
@@ -2737,7 +2737,7 @@ def spec_and_dependency_types(
         return spec_builder(spec_dict)
 
     @staticmethod
-    def from_dict(data):
+    def from_dict(data) -> "Spec":
         """Construct a spec from JSON/YAML.
 
         Args:
@@ -2760,7 +2760,7 @@ def from_dict(data):
         return spec
 
     @staticmethod
-    def from_yaml(stream):
+    def from_yaml(stream) -> "Spec":
         """Construct a spec from YAML.
 
         Args:
@@ -2770,7 +2770,7 @@ def from_yaml(stream):
         return Spec.from_dict(data)
 
     @staticmethod
-    def from_json(stream):
+    def from_json(stream) -> "Spec":
         """Construct a spec from JSON.
 
         Args:
@@ -2780,7 +2780,7 @@ def from_json(stream):
             data = sjson.load(stream)
             return Spec.from_dict(data)
         except Exception as e:
-            raise sjson.SpackJSONError("error parsing JSON spec:", str(e)) from e
+            raise sjson.SpackJSONError("error parsing JSON spec:", e) from e
 
     @staticmethod
     def extract_json_from_clearsig(data):
diff --git a/lib/spack/spack/test/build_environment.py b/lib/spack/spack/test/build_environment.py
index e4699f1f02f..14a09e85dcf 100644
--- a/lib/spack/spack/test/build_environment.py
+++ b/lib/spack/spack/test/build_environment.py
@@ -388,7 +388,7 @@ def test_wrapper_variables(
     root = spack.concretize.concretize_one("dt-diamond")
 
     for s in root.traverse():
-        s.prefix = "/{0}-prefix/".format(s.name)
+        s.set_prefix(f"/{s.name}-prefix/")
 
     dep_pkg = root["dt-diamond-left"].package
     dep_lib_paths = ["/test/path/to/ex1.so", "/test/path/to/subdir/ex2.so"]
@@ -396,7 +396,7 @@ def test_wrapper_variables(
     dep_libs = LibraryList(dep_lib_paths)
 
     dep2_pkg = root["dt-diamond-right"].package
-    dep2_pkg.spec.prefix = str(installation_dir_with_headers)
+    dep2_pkg.spec.set_prefix(str(installation_dir_with_headers))
 
     setattr(dep_pkg, "libs", dep_libs)
     try:
diff --git a/lib/spack/spack/test/build_systems.py b/lib/spack/spack/test/build_systems.py
index 6ed44395b91..e6b2594394f 100644
--- a/lib/spack/spack/test/build_systems.py
+++ b/lib/spack/spack/test/build_systems.py
@@ -403,8 +403,8 @@ def test_autoreconf_search_path_args_multiple(default_mock_concretization, tmpdi
     aclocal_fst = str(tmpdir.mkdir("fst").mkdir("share").mkdir("aclocal"))
     aclocal_snd = str(tmpdir.mkdir("snd").mkdir("share").mkdir("aclocal"))
     build_dep_one, build_dep_two = spec.dependencies(deptype="build")
-    build_dep_one.prefix = str(tmpdir.join("fst"))
-    build_dep_two.prefix = str(tmpdir.join("snd"))
+    build_dep_one.set_prefix(str(tmpdir.join("fst")))
+    build_dep_two.set_prefix(str(tmpdir.join("snd")))
     assert spack.build_systems.autotools._autoreconf_search_path_args(spec) == [
         "-I",
         aclocal_fst,
@@ -422,8 +422,8 @@ def test_autoreconf_search_path_args_skip_automake(default_mock_concretization,
     aclocal_snd = str(tmpdir.mkdir("snd").mkdir("share").mkdir("aclocal"))
     build_dep_one, build_dep_two = spec.dependencies(deptype="build")
     build_dep_one.name = "automake"
-    build_dep_one.prefix = str(tmpdir.join("fst"))
-    build_dep_two.prefix = str(tmpdir.join("snd"))
+    build_dep_one.set_prefix(str(tmpdir.join("fst")))
+    build_dep_two.set_prefix(str(tmpdir.join("snd")))
     assert spack.build_systems.autotools._autoreconf_search_path_args(spec) == ["-I", aclocal_snd]
 
 
@@ -434,7 +434,7 @@ def test_autoreconf_search_path_args_external_order(default_mock_concretization,
     aclocal_snd = str(tmpdir.mkdir("snd").mkdir("share").mkdir("aclocal"))
     build_dep_one, build_dep_two = spec.dependencies(deptype="build")
     build_dep_one.external_path = str(tmpdir.join("fst"))
-    build_dep_two.prefix = str(tmpdir.join("snd"))
+    build_dep_two.set_prefix(str(tmpdir.join("snd")))
     assert spack.build_systems.autotools._autoreconf_search_path_args(spec) == [
         "-I",
         aclocal_snd,
@@ -447,8 +447,8 @@ def test_autoreconf_search_path_skip_nonexisting(default_mock_concretization, tm
     """Skip -I flags for non-existing directories"""
     spec = default_mock_concretization("dttop")
     build_dep_one, build_dep_two = spec.dependencies(deptype="build")
-    build_dep_one.prefix = str(tmpdir.join("fst"))
-    build_dep_two.prefix = str(tmpdir.join("snd"))
+    build_dep_one.set_prefix(str(tmpdir.join("fst")))
+    build_dep_two.set_prefix(str(tmpdir.join("snd")))
     assert spack.build_systems.autotools._autoreconf_search_path_args(spec) == []
 
 
diff --git a/lib/spack/spack/test/verification.py b/lib/spack/spack/test/verification.py
index 57378fca324..768c95618a6 100644
--- a/lib/spack/spack/test/verification.py
+++ b/lib/spack/spack/test/verification.py
@@ -133,7 +133,7 @@ def test_check_prefix_manifest(tmpdir):
 
     spec = spack.spec.Spec("libelf")
     spec._mark_concrete()
-    spec.prefix = prefix
+    spec.set_prefix(prefix)
 
     results = spack.verify.check_spec_manifest(spec)
     assert results.has_errors()
diff --git a/lib/spack/spack/test/views.py b/lib/spack/spack/test/views.py
index c94b36fea52..4dbf167d24e 100644
--- a/lib/spack/spack/test/views.py
+++ b/lib/spack/spack/test/views.py
@@ -35,8 +35,8 @@ def test_view_with_spec_not_contributing_files(mock_packages, tmpdir):
 
     a = Spec("pkg-a")
     b = Spec("pkg-b")
-    a.prefix = os.path.join(tmpdir, "a")
-    b.prefix = os.path.join(tmpdir, "b")
+    a.set_prefix(os.path.join(tmpdir, "a"))
+    b.set_prefix(os.path.join(tmpdir, "b"))
     a._mark_concrete()
     b._mark_concrete()
 
diff --git a/lib/spack/spack/user_environment.py b/lib/spack/spack/user_environment.py
index 5c3cc5a6f87..90bb379b8e9 100644
--- a/lib/spack/spack/user_environment.py
+++ b/lib/spack/spack/user_environment.py
@@ -68,7 +68,9 @@ def project_env_mods(
     *specs: spack.spec.Spec, view, env: environment.EnvironmentModifications
 ) -> None:
     """Given a list of environment modifications, project paths changes to the view."""
-    prefix_to_prefix = {s.prefix: view.get_projection_for_spec(s) for s in specs if not s.external}
+    prefix_to_prefix = {
+        str(s.prefix): view.get_projection_for_spec(s) for s in specs if not s.external
+    }
     # Avoid empty regex if all external
     if not prefix_to_prefix:
         return