Fix using relative paths with --local-cache-dir and `--named-caches…

…-dir`

# Rust tests will be skipped. Delete if not intended.
[ci skip-rust-tests]

src/python/pants/init/engine_initializer.py

@@ -3,6 +3,7 @@
 
 import logging
 from dataclasses import dataclass
+from pathlib import Path
 from typing import Any, Iterable, List, Optional, Set, Tuple, Type, cast
 
 from pants.base.build_environment import get_buildroot
@@ -308,14 +309,17 @@ def build_root_singleton() -> BuildRoot:
 
         union_rules = build_configuration.union_rules()
 
+        def ensure_absolute_path(v: str) -> str:
+            return Path(v).resolve().as_posix()
+
         scheduler = Scheduler(
             native=native,
             ignore_patterns=pants_ignore_patterns,
             use_gitignore=use_gitignore,
             build_root=build_root,
-            local_store_dir=local_store_dir,
-            local_execution_root_dir=local_execution_root_dir,
-            named_caches_dir=named_caches_dir,
+            local_store_dir=ensure_absolute_path(local_store_dir),
+            local_execution_root_dir=ensure_absolute_path(local_execution_root_dir),
+            named_caches_dir=ensure_absolute_path(named_caches_dir),
             rules=rules,
             union_rules=union_rules,
             execution_options=execution_options,

src/python/pants/option/global_options.py

@@ -667,10 +667,17 @@ def register_bootstrap_options(cls, register):
             "other, or override symbols from each other.",
         )
 
+        cache_instructions = (
+            "The path may be absolute or relative. If the directory is within the build root, be "
+            "sure to include it in `--pants-ignore`."
+        )
         register(
             "--local-store-dir",
             advanced=True,
-            help="Directory to use for engine's local file store.",
+            help=(
+                f"Directory to use for the local file store, which stores the results of "
+                f"subprocesses run by Pants. {cache_instructions}"
+            ),
             # This default is also hard-coded into the engine's rust code in
             # fs::Store::default_path so that tools using a Store outside of pants
             # are likely to be able to use the same storage location.
@@ -679,14 +686,19 @@ def register_bootstrap_options(cls, register):
         register(
             "--local-execution-root-dir",
             advanced=True,
-            help="Directory to use for engine's local process execution sandboxing.",
+            help=(
+                "Directory to use for local process execution sandboxing. "
+                f"{cache_instructions}"
+            ),
             default=tempfile.gettempdir(),
         )
         register(
             "--named-caches-dir",
             advanced=True,
-            help="Directory to use as the base for named global caches for processes with "
-            "trusted, concurrency-safe caches.",
+            help=(
+                "Directory to use for named global caches for tools and processes with trusted, "
+                f"concurrency-safe caches. {cache_instructions}"
+            ),
             default=os.path.join(get_pants_cachedir(), "named_caches"),
         )
         register(