from __future__ import unicode_literals

import contextlib
import os.path

import toml

import pre_commit.constants as C
from pre_commit.envcontext import envcontext
from pre_commit.envcontext import Var
from pre_commit.languages import helpers
from pre_commit.util import clean_path_on_failure
from pre_commit.util import cmd_output


ENVIRONMENT_DIR = 'rustenv'
get_default_version = helpers.basic_get_default_version
healthy = helpers.basic_healthy


def get_env_patch(target_dir):
    return (
        (
            'PATH',
            (os.path.join(target_dir, 'bin'), os.pathsep, Var('PATH')),
        ),
    )


@contextlib.contextmanager
def in_env(prefix):
    target_dir = prefix.path(
        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
    )
    with envcontext(get_env_patch(target_dir)):
        yield


def _add_dependencies(cargo_toml_path, additional_dependencies):
    with open(cargo_toml_path, 'r+') as f:
        cargo_toml = toml.load(f)
        cargo_toml.setdefault('dependencies', {})
        for dep in additional_dependencies:
            name, _, spec = dep.partition(':')
            cargo_toml['dependencies'][name] = spec or '*'
        f.seek(0)
        toml.dump(cargo_toml, f)
        f.truncate()


def install_environment(prefix, version, additional_dependencies):
    helpers.assert_version_default('rust', version)
    directory = prefix.path(
        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
    )

    # There are two cases where we might want to specify more dependencies:
    # as dependencies for the library being built, and as binary packages
    # to be `cargo install`'d.
    #
    # Unlike e.g. Python, if we just `cargo install` a library, it won't be
    # used for compilation. And if we add a crate providing a binary to the
    # `Cargo.toml`, the binary won't be built.
    #
    # Because of this, we allow specifying "cli" dependencies by prefixing
    # with 'cli:'.
    cli_deps = {
        dep for dep in additional_dependencies if dep.startswith('cli:')
    }
    lib_deps = set(additional_dependencies) - cli_deps

    if len(lib_deps) > 0:
        _add_dependencies(prefix.path('Cargo.toml'), lib_deps)

    with clean_path_on_failure(directory):
        packages_to_install = {()}
        for cli_dep in cli_deps:
            cli_dep = cli_dep[len('cli:'):]
            package, _, version = cli_dep.partition(':')
            if version != '':
                packages_to_install.add((package, '--version', version))
            else:
                packages_to_install.add((package,))

        for package in packages_to_install:
            cmd_output(
                'cargo', 'install', '--bins', '--root', directory, *package,
                cwd=prefix.prefix_dir
            )


def run_hook(hook, file_args):
    with in_env(hook.prefix):
        return helpers.run_xargs(hook, helpers.to_cmd(hook), file_args)

pre_commit/languages/rust.py
from __future__ import unicode_literals

import contextlib
import os.path

import toml

import pre_commit.constants as C
from pre_commit.envcontext import envcontext
from pre_commit.envcontext import Var
from pre_commit.languages import helpers
from pre_commit.util import clean_path_on_failure
from pre_commit.util import cmd_output


ENVIRONMENT_DIR = 'rustenv'
get_default_version = helpers.basic_get_default_version
healthy = helpers.basic_healthy


def get_env_patch(target_dir):
    return (
        (
            'PATH',
            (os.path.join(target_dir, 'bin'), os.pathsep, Var('PATH')),
        ),
    )


@contextlib.contextmanager
def in_env(prefix):
    target_dir = prefix.path(
        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
    )
    with envcontext(get_env_patch(target_dir)):
        yield


def _add_dependencies(cargo_toml_path, additional_dependencies):
    with open(cargo_toml_path, 'r+') as f:
        cargo_toml = toml.load(f)
        cargo_toml.setdefault('dependencies', {})
        for dep in additional_dependencies:
            name, _, spec = dep.partition(':')
            cargo_toml['dependencies'][name] = spec or '*'
        f.seek(0)
        toml.dump(cargo_toml, f)
        f.truncate()


def install_environment(prefix, version, additional_dependencies):
    helpers.assert_version_default('rust', version)
    directory = prefix.path(
        helpers.environment_dir(ENVIRONMENT_DIR, C.DEFAULT),
    )

    # There are two cases where we might want to specify more dependencies:
    # as dependencies for the library being built, and as binary packages
    # to be `cargo install`'d.
    #
    # Unlike e.g. Python, if we just `cargo install` a library, it won't be
    # used for compilation. And if we add a crate providing a binary to the
    # `Cargo.toml`, the binary won't be built.
    #
    # Because of this, we allow specifying "cli" dependencies by prefixing
    # with 'cli:'.
    cli_deps = {
        dep for dep in additional_dependencies if dep.startswith('cli:')
    }
    lib_deps = set(additional_dependencies) - cli_deps

    if len(lib_deps) > 0:
        _add_dependencies(prefix.path('Cargo.toml'), lib_deps)

    with clean_path_on_failure(directory):
        packages_to_install = {('--path', '.')}
        for cli_dep in cli_deps:
            cli_dep = cli_dep[len('cli:'):]
            package, _, version = cli_dep.partition(':')
            if version != '':
                packages_to_install.add((package, '--version', version))
            else:
                packages_to_install.add((package,))

        for package in packages_to_install:
            cmd_output(
                'cargo', 'install', '--bins', '--root', directory, *package,
                cwd=prefix.prefix_dir
            )


def run_hook(hook, file_args):
    with in_env(hook.prefix):
        return helpers.run_xargs(hook, helpers.to_cmd(hook), file_args)

pre_commit/languages/rust.py
diff --git a/pre_commit/languages/rust.py b/pre_commit/languages/rust.py
index e09d0078f..4b25a9d10 100644
--- a/pre_commit/languages/rust.py
+++ b/pre_commit/languages/rust.py
@@ -73,7 +73,7 @@ def install_environment(prefix, version, additional_dependencies):
         _add_dependencies(prefix.path('Cargo.toml'), lib_deps)
 
     with clean_path_on_failure(directory):
-        packages_to_install = {()}
+        packages_to_install = {('--path', '.')}
         for cli_dep in cli_deps:
             cli_dep = cli_dep[len('cli:'):]
             package, _, version = cli_dep.partition(':')

rust hook requires `--path` attribute
Cargo has changed how packages get installed and requires an extra `--path <destination>` attribute.

Symptom:
```
[INFO] Initializing environment for https://github.com/nix-community/nixpkgs-fmt.
[INFO] Installing environment for https://github.com/nix-community/nixpkgs-fmt.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
An unexpected error has occurred: CalledProcessError: Command: ('/nix/store/fcc3x8zwq1c0667xjs7bkn6ay8j4fdpz-rust-1.38.0-nightly-2019-08-07-ad7c55e1f/bin/cargo', 'install', '--bins', '--root', '/home/zimbatm/.cache/pre-commit/repoeft6xm6t/rustenv-default')
Return code: 101
Expected return code: 0
Output: (none)
Errors: 
    error: Using `cargo install` to install the binaries for the package in current working directory is no longer supported, use `cargo install --path .` instead. Use `cargo build` if you want to simply build the package.
```

I guess the fix should be done where here: https://github.com/pre-commit/pre-commit/blob/9c6a1d80d6b94c86a1785a40a51389e83accac3e/pre_commit/languages/rust.py#L87

Do we want to make pre-commit compatible with multiple versions of cargo or just the latest one?

/cc @asottile @chriskuehl 
