From c0cb319b6ccf1acd97ea4d46c8ca999d7a3e31db Mon Sep 17 00:00:00 2001
From: Jon Gjengset <jongje@amazon.com>
Date: Mon, 8 Feb 2021 17:29:06 -0800
Subject: [PATCH] Allow setting cargo home from .cargo/home

This patch allows users to set the Cargo home directory through the file
system using a pointer file in `.cargo/home`. As with `.cargo/config`,
the file is searched for recursively up the tree from the current
working directory. Unlike with `.cargo/config`, the search terminates
when a matching file is found.

The search for `.cargo/home` happens before any `.cargo/config` files
are read, as that may be affected by the choice of Cargo home directory.

The `CARGO_HOME` environment variable is preferred over `.cargo/home`.

Fixes #6452.
---
 src/cargo/util/config/mod.rs     | 41 +++++++++++++----
 tests/testsuite/cargo_command.rs | 79 ++++++++++++++++++++++++++++++++
 2 files changed, 111 insertions(+), 9 deletions(-)

diff --git a/src/cargo/util/config/mod.rs b/src/cargo/util/config/mod.rs
index 3302a027e8c..4c074b2f2d3 100644
--- a/src/cargo/util/config/mod.rs
+++ b/src/cargo/util/config/mod.rs
@@ -63,7 +63,7 @@ use std::str::FromStr;
 use std::sync::Once;
 use std::time::Instant;
 
-use anyhow::{anyhow, bail, format_err};
+use anyhow::{anyhow, bail, format_err, Context};
 use curl::easy::Easy;
 use lazycell::LazyCell;
 use serde::Deserialize;
@@ -260,12 +260,7 @@ impl Config {
         let shell = Shell::new();
         let cwd =
             env::current_dir().chain_err(|| "couldn't get the current directory of the process")?;
-        let homedir = homedir(&cwd).ok_or_else(|| {
-            anyhow!(
-                "Cargo couldn't find your home directory. \
-                 This probably means that $HOME was not set."
-            )
-        })?;
+        let homedir = homedir(&cwd)?;
         Ok(Config::new(shell, cwd, homedir))
     }
 
@@ -1618,8 +1613,36 @@ impl ConfigValue {
     }
 }
 
-pub fn homedir(cwd: &Path) -> Option<PathBuf> {
-    ::home::cargo_home_with_cwd(cwd).ok()
+pub fn homedir(cwd: &Path) -> CargoResult<PathBuf> {
+    if std::env::var_os("CARGO_HOME")
+        .filter(|h| !h.is_empty())
+        .is_none()
+    {
+        // CARGO_HOME is not set -- look for a .cargo/home file instead
+        let mut components = cwd.components();
+        loop {
+            let cargo_home = components.as_path().join(".cargo/home");
+            if cargo_home.exists() {
+                let home = std::fs::read_to_string(&cargo_home).with_context(|| {
+                    format!(
+                        "Cargo could not follow home pointer in '{}'",
+                        cargo_home.display()
+                    )
+                })?;
+                return Ok(PathBuf::from(home));
+            }
+            if components.next_back().is_none() {
+                break;
+            }
+        }
+    }
+
+    ::home::cargo_home_with_cwd(cwd).map_err(|_| {
+        anyhow!(
+            "Cargo couldn't find your home directory. \
+             This probably means that $HOME was not set."
+        )
+    })
 }
 
 pub fn save_credentials(
diff --git a/tests/testsuite/cargo_command.rs b/tests/testsuite/cargo_command.rs
index 04e3051c785..a3439a702af 100644
--- a/tests/testsuite/cargo_command.rs
+++ b/tests/testsuite/cargo_command.rs
@@ -271,6 +271,85 @@ fn override_cargo_home() {
     assert!(contents.contains(r#"authors = ["foo <bar>"]"#));
 }
 
+#[cargo_test]
+fn cargo_home_pointer() {
+    let root = paths::root();
+    let my_home = root.join("my_home");
+    fs::create_dir(&my_home).unwrap();
+    fs::write(
+        &my_home.join("config"),
+        r#"
+            [cargo-new]
+            name = "foo"
+            email = "bar"
+            git = false
+        "#,
+    )
+    .unwrap();
+
+    fs::create_dir(root.join(".cargo")).unwrap();
+    fs::write(
+        root.join(".cargo/home"),
+        my_home.as_os_str().to_str().unwrap().as_bytes(),
+    )
+    .unwrap();
+
+    cargo_process("new foo")
+        .env("USER", "foo")
+        .env_remove("CARGO_HOME")
+        .run();
+
+    let toml = paths::root().join("foo/Cargo.toml");
+    let contents = fs::read_to_string(&toml).unwrap();
+    assert!(contents.contains(r#"authors = ["foo <bar>"]"#));
+}
+
+#[cargo_test]
+fn cargo_home_prefer_env() {
+    let root = paths::root();
+    let my_home = root.join("my_home");
+    fs::create_dir(&my_home).unwrap();
+    fs::write(
+        &my_home.join("config"),
+        r#"
+            [cargo-new]
+            name = "foo"
+            email = "bar"
+            git = false
+        "#,
+    )
+    .unwrap();
+
+    let my_other_home = root.join("my_other_home");
+    fs::create_dir(&my_other_home).unwrap();
+    fs::write(
+        &my_other_home.join("config"),
+        r#"
+            [cargo-new]
+            name = "foo"
+            email = "baz"
+            git = false
+        "#,
+    )
+    .unwrap();
+
+    fs::create_dir(root.join(".cargo")).unwrap();
+    fs::write(
+        root.join(".cargo/home"),
+        my_other_home.as_os_str().to_str().unwrap().as_bytes(),
+    )
+    .unwrap();
+
+    cargo_process("new foo")
+        .env("USER", "foo")
+        .env("CARGO_HOME", &my_home)
+        .run();
+
+    let toml = paths::root().join("foo/Cargo.toml");
+    let contents = fs::read_to_string(&toml).unwrap();
+    assert!(contents.contains(r#"authors = ["foo <bar>"]"#));
+}
+
 #[cargo_test]
 fn cargo_subcommand_env() {
     let src = format!(