Update environment variables doc (#5994)

## Summary

This PR adds descriptions for the `UV_TOOL_DIR`, `UV_PYTHON_INSTALL_DIR`
and `XDG_*` environment variables.

Additionally, it moves some env vars that are not command-line arguments
to the below "uv respects" section.

Closes #5746

README.md

@@ -600,24 +600,33 @@ uv accepts the following command-line arguments as environment variables:
   a link mode.
 - `UV_NO_BUILD_ISOLATION`: Equivalent to the `--no-build-isolation` command-line argument. If set,
   uv will skip isolation when building source distributions.
-- `UV_CUSTOM_COMPILE_COMMAND`: Used to override `uv` in the output header of the `requirements.txt`
-  files generated by `uv pip compile`. Intended for use-cases in which `uv pip compile` is called
-  from within a wrapper script, to include the name of the wrapper script in the output file.
+- `UV_CUSTOM_COMPILE_COMMAND`: Equivalent to the `--custom-compile-command` command-line argument.
+  Used to override uv in the output header of the `requirements.txt` files generated by
+  `uv pip compile`. Intended for use-cases in which `uv pip compile` is called from within a wrapper
+  script, to include the name of the wrapper script in the output file.
 - `UV_KEYRING_PROVIDER`: Equivalent to the `--keyring-provider` command-line argument. If set, uv
   will use this value as the keyring provider.
 - `UV_CONFIG_FILE`: Equivalent to the `--config-file` command-line argument. Expects a path to a
   local `uv.toml` file to use as the configuration file.
 - `UV_NO_CONFIG`: Equivalent to the `--no-config` command-line argument. If set, uv will not read
   any configuration files from the current directory, parent directories, or user configuration
   directories.
-- `UV_CONCURRENT_DOWNLOADS`: Sets the maximum number of in-flight concurrent downloads that `uv`
-  will perform at any given time.
-- `UV_CONCURRENT_BUILDS`: Sets the maximum number of source distributions that `uv` will build
+- `UV_EXCLUDE_NEWER`: Equivalent to the `--exclude-newer` command-line argument. If set, uv will
+  exclude distributions published after the specified date.
+
+In each case, the corresponding command-line argument takes precedence over an environment variable.
+
+In addition, uv respects the following environment variables:
+
+- `UV_CONCURRENT_DOWNLOADS`: Sets the maximum number of in-flight concurrent downloads that uv will
+  perform at any given time.
+- `UV_CONCURRENT_BUILDS`: Sets the maximum number of source distributions that uv will build
   concurrently at any given time.
 - `UV_CONCURRENT_INSTALLS`: Used to control the number of threads used when installing and unzipping
   packages.
-- `UV_EXCLUDE_NEWER`: Equivalent to the `--exclude-newer` command-line argument. If set, uv will
-  exclude distributions published after the specified date.
+- `UV_TOOL_DIR`: Used to specify the directory where uv will store managed tools.
+- `UV_PYTHON_INSTALL_DIR`: Used to specify the directory where uv will store managed Python
+  installations.
 - `UV_PYTHON_INSTALL_MIRROR`: Managed Python installations are downloaded from
   [`python-build-standalone`](https://github.com/indygreg/python-build-standalone). This variable
   can be set to a mirror URL to use a different source for Python installations. The provided URL
@@ -628,11 +637,12 @@ uv accepts the following command-line arguments as environment variables:
   different source for PyPy installations. The provided URL will replace
   `https://downloads.python.org/pypy` in, e.g.,
   `https://downloads.python.org/pypy/pypy3.8-v7.3.7-osx64.tar.bz2`.
-
-In each case, the corresponding command-line argument takes precedence over an environment variable.
-
-In addition, uv respects the following environment variables:
-
+- `XDG_CONFIG_HOME`: Used to specify the path to uv user-level configuration directory on Linux
+  _and_ macOS systems.
+- `XDG_CACHE_HOME`: Used to specify the directory where uv stores cache files on Linux system.
+- `XDG_DATA_HOME`: Used to specify the directory where uv stores managed Python installations and
+  managed tools on Linux system.
+- `XDG_BIN_HOME`: Used to specify the directory where executables are installed into.
 - `SSL_CERT_FILE`: If set, uv will use this file as the certificate bundle instead of the system's
   trust store.
 - `SSL_CLIENT_CERT`: If set, uv will use this file for mTLS authentication. This should be a single

docs/configuration/environment.md

@@ -34,25 +34,42 @@ uv accepts the following command-line arguments as environment variables:
   uv will require that all dependencies have a hash specified in the requirements file.
 - `UV_CONSTRAINT`: Equivalent to the `--constraint` command-line argument. If set, uv will use this
   file as the constraints file. Uses space-separated list of files.
+- `UV_BUILD_CONSTRAINT`: Equivalent to the `--build-constraint` command-line argument. If set, uv
+  will use this file as constraints for any source distribution builds. Uses space-separated list of
+  files.
+- `UV_OVERRIDE`: Equivalent to the `--override` command-line argument. If set, uv will use this file
+  as the overrides file. Uses space-separated list of files.
 - `UV_LINK_MODE`: Equivalent to the `--link-mode` command-line argument. If set, uv will use this as
   a link mode.
 - `UV_NO_BUILD_ISOLATION`: Equivalent to the `--no-build-isolation` command-line argument. If set,
   uv will skip isolation when building source distributions.
-- `UV_CUSTOM_COMPILE_COMMAND`: Used to override uv in the output header of the `requirements.txt`
-  files generated by `uv pip compile`. Intended for use-cases in which `uv pip compile` is called
-  from within a wrapper script, to include the name of the wrapper script in the output file.
+- `UV_CUSTOM_COMPILE_COMMAND`: Equivalent to the `--custom-compile-command` command-line argument.
+  Used to override uv in the output header of the `requirements.txt` files generated by
+  `uv pip compile`. Intended for use-cases in which `uv pip compile` is called from within a wrapper
+  script, to include the name of the wrapper script in the output file.
 - `UV_KEYRING_PROVIDER`: Equivalent to the `--keyring-provider` command-line argument. If set, uv
   will use this value as the keyring provider.
 - `UV_CONFIG_FILE`: Equivalent to the `--config-file` command-line argument. Expects a path to a
   local `uv.toml` file to use as the configuration file.
+- `UV_NO_CONFIG`: Equivalent to the `--no-config` command-line argument. If set, uv will not read
+  any configuration files from the current directory, parent directories, or user configuration
+  directories.
+- `UV_EXCLUDE_NEWER`: Equivalent to the `--exclude-newer` command-line argument. If set, uv will
+  exclude distributions published after the specified date.
+
+In each case, the corresponding command-line argument takes precedence over an environment variable.
+
+In addition, uv respects the following environment variables:
+
 - `UV_CONCURRENT_DOWNLOADS`: Sets the maximum number of in-flight concurrent downloads that uv will
   perform at any given time.
 - `UV_CONCURRENT_BUILDS`: Sets the maximum number of source distributions that uv will build
   concurrently at any given time.
 - `UV_CONCURRENT_INSTALLS`: Used to control the number of threads used when installing and unzipping
   packages.
-- `UV_EXCLUDE_NEWER`: Equivalent to the `--exclude-newer` command-line argument. If set, uv will
-  exclude distributions published after the specified date.
+- `UV_TOOL_DIR`: Used to specify the directory where uv will store managed tools.
+- `UV_PYTHON_INSTALL_DIR`: Used to specify the directory where uv will store managed Python
+  installations.
 - `UV_PYTHON_INSTALL_MIRROR`: Managed Python installations are downloaded from
   [`python-build-standalone`](https://github.com/indygreg/python-build-standalone). This variable
   can be set to a mirror URL to use a different source for Python installations. The provided URL
@@ -63,11 +80,12 @@ uv accepts the following command-line arguments as environment variables:
   different source for PyPy installations. The provided URL will replace
   `https://downloads.python.org/pypy` in, e.g.,
   `https://downloads.python.org/pypy/pypy3.8-v7.3.7-osx64.tar.bz2`.
-
-In each case, the corresponding command-line argument takes precedence over an environment variable.
-
-In addition, uv respects the following environment variables:
-
+- `XDG_CONFIG_HOME`: Used to specify the path to uv user-level configuration directory on Linux
+  _and_ macOS systems.
+- `XDG_CACHE_HOME`: Used to specify the directory where uv stores cache files on Linux system.
+- `XDG_DATA_HOME`: Used to specify the directory where uv stores managed Python installations and
+  managed tools on Linux system.
+- `XDG_BIN_HOME`: Used to specify the directory where executables are installed into.
 - `SSL_CERT_FILE`: If set, uv will use this file as the certificate bundle instead of the system's
   trust store.
 - `SSL_CLIENT_CERT`: If set, uv will use this file for mTLS authentication. This should be a single