[WIP] Add support for platform-defined standard directories

This change stops cargo from violating the operating system rules
regarding the placement of config, cache, ... directories on Linux,
macOS and Windows.

Existing directories and overrides are retained.

The precedence is as follows:

1) use the `CARGO_HOME` environment variable if it exists (legacy)
2) use `CARGO_CACHE_DIR`, `CARGO_CONFIG_DIR` etc. env vars if they exist
3) use the ~/.cargo directory if it exists (legacy)
4) follow operating system standards

A new cargo command, `dirs`,  is added, which can provide path
information to other command line tools.

Fixes:
  #1734
  #1976
  rust-lang/rust#12725

Addresses:
  rust-lang/rfcs#1615
  #148,
  #3981

Cargo.toml

@@ -22,6 +22,7 @@ crates-io = { path = "src/crates-io", version = "0.16" }
 crossbeam = "0.3"
 crypto-hash = "0.3"
 curl = "0.4.6"
+directories = "0.8.0"
 env_logger = "0.5"
 failure = "0.1.1"
 filetime = "0.1"

src/bin/cargo.rs

@@ -174,7 +174,7 @@ fn is_executable<P: AsRef<Path>>(path: P) -> bool {
 }
 
 fn search_directories(config: &Config) -> Vec<PathBuf> {
-    let mut dirs = vec![config.home().clone().into_path_unlocked().join("bin")];
+    let mut dirs = vec![config.bin_path()];
     if let Some(val) = env::var_os("PATH") {
         dirs.extend(env::split_paths(&val));
     }

src/bin/commands/dirs.rs

@@ -0,0 +1,16 @@
+use command_prelude::*;
+
+pub fn cli() -> App {
+    subcommand("dirs")
+        .about("Display directories (cache, config, ...) used by cargo")
+        .after_help("\
+")
+}
+
+pub fn exec(config: &mut Config, _args: &ArgMatches) -> CliResult {
+    println!("CARGO_CACHE_DIR:  {:?}", config.cache_path().into_path_unlocked());
+    println!("CARGO_CONFIG_DIR: {:?}", config.config_path().into_path_unlocked());
+    println!("CARGO_DATA_DIR:   {:?}", config.data_path());
+    println!("CARGO_BIN_DIR:    {:?}", config.bin_path());
+    Ok(())
+}

src/bin/commands/mod.rs

@@ -6,6 +6,7 @@ pub fn builtin() -> Vec<App> {
         build::cli(),
         check::cli(),
         clean::cli(),
+        dirs::cli(),
         doc::cli(),
         fetch::cli(),
         generate_lockfile::cli(),
@@ -40,6 +41,7 @@ pub fn builtin_exec(cmd: &str) -> Option<fn(&mut Config, &ArgMatches) -> CliResu
         "build" => build::exec,
         "check" => check::exec,
         "clean" => clean::exec,
+        "dirs" => dirs::exec,
         "doc" => doc::exec,
         "fetch" => fetch::exec,
         "generate-lockfile" => generate_lockfile::exec,
@@ -74,6 +76,7 @@ pub mod bench;
 pub mod build;
 pub mod check;
 pub mod clean;
+pub mod dirs;
 pub mod doc;
 pub mod fetch;
 pub mod generate_lockfile;

src/cargo/core/workspace.rs

@@ -373,7 +373,7 @@ impl<'cfg> Workspace<'cfg> {
             // `CARGO_HOME` pointing inside of the workspace root or in the
             // current project, but we don't want to mistakenly try to put
             // crates.io crates into the workspace by accident.
-            if self.config.home() == path {
+            if &self.config.cache_path() == path {
                 break;
             }
         }

src/cargo/lib.rs

@@ -11,6 +11,7 @@ extern crate core_foundation;
 extern crate crates_io as registry;
 extern crate crossbeam;
 extern crate curl;
+extern crate directories;
 #[macro_use]
 extern crate failure;
 extern crate filetime;

src/cargo/ops/cargo_install.rs

@@ -53,6 +53,27 @@ impl Drop for Transaction {
     }
 }
 
+#[derive(Clone)]
+struct CargoInstallDirs {
+    config_dir: PathBuf,
+    bin_dir: PathBuf,
+}
+
+impl CargoInstallDirs {
+    fn from_root(root: PathBuf) -> CargoInstallDirs {
+        CargoInstallDirs {
+            bin_dir: root.join("bin"),
+            config_dir: root,
+        }
+    }
+    fn from_config(config: &Config) -> CargoInstallDirs {
+        CargoInstallDirs {
+            config_dir: config.config_path().into_path_unlocked(),
+            bin_dir: config.bin_path(),
+        }
+    }
+}
+
 pub fn install(
     root: Option<&str>,
     krates: Vec<&str>,
@@ -61,7 +82,7 @@ pub fn install(
     opts: &ops::CompileOptions,
     force: bool,
 ) -> CargoResult<()> {
-    let root = resolve_root(root, opts.config)?;
+    let root = resolve_install_dirs(root, opts.config)?;
     let map = SourceConfigMap::new(opts.config)?;
 
     let (installed_anything, scheduled_error) = if krates.len() <= 1 {
@@ -122,7 +143,7 @@ pub fn install(
     if installed_anything {
         // Print a warning that if this directory isn't in PATH that they won't be
         // able to run these commands.
-        let dst = metadata(opts.config, &root)?.parent().join("bin");
+        let dst = metadata(opts.config, &Filesystem::new(root.config_dir))?.parent().join("bin");
         let path = env::var_os("PATH").unwrap_or_default();
         for path in env::split_paths(&path) {
             if path == dst {
@@ -145,7 +166,7 @@ pub fn install(
 }
 
 fn install_one(
-    root: &Filesystem,
+    dirs: &CargoInstallDirs,
     map: &SourceConfigMap,
     krate: Option<&str>,
     source_id: &SourceId,
@@ -235,9 +256,9 @@ fn install_one(
     // We have to check this again afterwards, but may as well avoid building
     // anything if we're gonna throw it away anyway.
     {
-        let metadata = metadata(config, root)?;
+        let metadata = metadata(config, &Filesystem::new(dirs.config_dir.clone()))?;
         let list = read_crate_list(&metadata)?;
-        let dst = metadata.parent().join("bin");
+        let dst = config.bin_path();
         check_overwrites(&dst, pkg, &opts.filter, &list, force)?;
     }
 
@@ -274,7 +295,7 @@ fn install_one(
         );
     }
 
-    let metadata = metadata(config, root)?;
+    let metadata = metadata(config, &Filesystem::new(dirs.config_dir.clone()))?;
     let mut list = read_crate_list(&metadata)?;
     let dst = metadata.parent().join("bin");
     let duplicates = check_overwrites(&dst, pkg, &opts.filter, &list, force)?;
@@ -653,8 +674,8 @@ fn write_crate_list(file: &FileLock, listing: CrateListingV1) -> CargoResult<()>
 }
 
 pub fn install_list(dst: Option<&str>, config: &Config) -> CargoResult<()> {
-    let dst = resolve_root(dst, config)?;
-    let dst = metadata(config, &dst)?;
+    let dst = resolve_install_dirs(dst, config)?;
+    let dst = metadata(config, &Filesystem::new(dst.config_dir))?;
     let list = read_crate_list(&dst)?;
     for (k, v) in list.v1.iter() {
         println!("{}:", k);
@@ -675,7 +696,7 @@ pub fn uninstall(
         bail!("A binary can only be associated with a single installed package, specifying multiple specs with --bin is redundant.");
     }
 
-    let root = resolve_root(root, config)?;
+    let root = resolve_install_dirs(root, config)?;
     let scheduled_error = if specs.len() == 1 {
         uninstall_one(&root, specs[0], bins, config)?;
         false
@@ -721,13 +742,13 @@ pub fn uninstall(
     Ok(())
 }
 
-pub fn uninstall_one(
-    root: &Filesystem,
+fn uninstall_one(
+    dirs: &CargoInstallDirs,
     spec: &str,
     bins: &[String],
     config: &Config,
 ) -> CargoResult<()> {
-    let crate_metadata = metadata(config, root)?;
+    let crate_metadata = metadata(config, &Filesystem::new(dirs.config_dir.clone()))?;
     let mut metadata = read_crate_list(&crate_metadata)?;
     let mut to_remove = Vec::new();
     {
@@ -736,7 +757,7 @@ pub fn uninstall_one(
             Entry::Occupied(e) => e,
             Entry::Vacant(..) => panic!("entry not found: {}", result),
         };
-        let dst = crate_metadata.parent().join("bin");
+        let dst = &dirs.bin_dir;
         for bin in installed.get() {
             let bin = dst.join(bin);
             if fs::metadata(&bin).is_err() {
@@ -785,15 +806,22 @@ pub fn uninstall_one(
     Ok(())
 }
 
+/// Return a file lock for the .crates.toml file at the given root.
+/// The config argument is only used for logging to the shell.
 fn metadata(config: &Config, root: &Filesystem) -> CargoResult<FileLock> {
     root.open_rw(Path::new(".crates.toml"), config, "crate metadata")
 }
 
-fn resolve_root(flag: Option<&str>, config: &Config) -> CargoResult<Filesystem> {
+// Determine cargo directories by first checking whether an argument was given
+// on the command line, if not checking whether the environment variable
+// CARGO_INSTALL_ROOT is set, and if not using the paths of the configuration.
+fn resolve_install_dirs(
+    root: Option<&str>,
+    config: &Config,
+) -> CargoResult<CargoInstallDirs> {
     let config_root = config.get_path("install.root")?;
-    Ok(flag.map(PathBuf::from)
+    Ok(root.map(PathBuf::from)
         .or_else(|| env::var_os("CARGO_INSTALL_ROOT").map(PathBuf::from))
-        .or_else(move || config_root.map(|v| v.val))
-        .map(Filesystem::new)
-        .unwrap_or_else(|| config.home().clone()))
+        .or_else(move || config_root.map(|v| v.val)).map(CargoInstallDirs::from_root)
+        .unwrap_or_else(|| CargoInstallDirs::from_config(config)))
 }