Propagate .cargo/config.toml [env] settings to the process environment

Environment variables can be set and optionally override the process
environment through `.cargo/config.toml`'s `[env]` section:
https://doc.rust-lang.org/cargo/reference/config.html#env

These config variables have specific precedence rules with regards to
overriding the environment set in the process, and can optionally
represent paths relative to the parent of the containing `.cargo/`
folder.

Besides exposing variables to all other processes called by `xbuild`,
this also allows `xbuild` itself to be driven by variables set in
`.cargo/config.toml`, such as `$ANDROID_HOME` needed for #116.

rust-mobile/cargo-subcommand#12
rust-mobile/cargo-subcommand#16

Author: MarijnS95

xbuild/src/cargo/config.rs

@@ -1,33 +1,268 @@
-use anyhow::Result;
+use anyhow::{Context, Result};
 use serde::Deserialize;
-use std::path::Path;
+use std::{
+    borrow::Cow,
+    collections::BTreeMap,
+    env::VarError,
+    ops::Deref,
+    path::{Path, PathBuf},
+};
 
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize, PartialEq, Eq)]
+#[serde(rename_all = "kebab-case")]
 pub struct Config {
     pub build: Option<Build>,
+    /// <https://doc.rust-lang.org/cargo/reference/config.html#env>
+    pub env: Option<BTreeMap<String, EnvOption>>,
 }
 
 impl Config {
     pub fn parse_from_toml(path: impl AsRef<Path>) -> Result<Self> {
         let contents = std::fs::read_to_string(path)?;
         Ok(toml::from_str(&contents)?)
     }
+}
+
+#[derive(Debug)]
+pub struct LocalizedConfig {
+    pub config: Config,
+    /// The directory containing `./.cargo/config.toml`
+    pub workspace: PathBuf,
+}
+
+impl Deref for LocalizedConfig {
+    type Target = Config;
+
+    fn deref(&self) -> &Self::Target {
+        &self.config
+    }
+}
+
+impl LocalizedConfig {
+    pub fn new(workspace: PathBuf) -> Result<Self> {
+        Ok(Self {
+            config: Config::parse_from_toml(workspace.join(".cargo/config.toml"))?,
+            workspace,
+        })
+    }
 
     /// Search for and open `.cargo/config.toml` in any parent of the workspace root path.
     pub fn find_cargo_config_for_workspace(workspace: impl AsRef<Path>) -> Result<Option<Self>> {
         let workspace = workspace.as_ref();
         let workspace = dunce::canonicalize(workspace)?;
         workspace
             .ancestors()
-            .map(|dir| dir.join(".cargo/config.toml"))
-            .find(|p| p.is_file())
-            .map(Config::parse_from_toml)
+            .find(|dir| dir.join(".cargo/config.toml").is_file())
+            .map(|p| p.to_path_buf())
+            .map(Self::new)
             .transpose()
     }
+
+    /// Propagate environment variables from this `.cargo/config.toml` to the process environment
+    /// using [`std::env::set_var()`].
+    ///
+    /// Note that this is automatically performed when calling [`Subcommand::new()`][super::Subcommand::new()].
+    pub fn set_env_vars(&self) -> Result<()> {
+        if let Some(env) = &self.config.env {
+            for (key, env_option) in env {
+                // Existing environment variables always have precedence unless
+                // the extended format is used to set `force = true`:
+                if !matches!(env_option, EnvOption::Value { force: true, .. })
+                    && std::env::var_os(key).is_some()
+                {
+                    continue;
+                }
+
+                std::env::set_var(key, env_option.resolve_value(&self.workspace)?.as_ref())
+            }
+        }
+
+        Ok(())
+    }
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Clone, Debug, Deserialize, PartialEq, Eq)]
 pub struct Build {
-    #[serde(rename = "target-dir")]
     pub target_dir: Option<String>,
 }
+
+/// Serializable environment variable in cargo config, configurable as per
+/// <https://doc.rust-lang.org/cargo/reference/config.html#env>,
+#[derive(Clone, Debug, Deserialize, PartialEq, Eq)]
+#[serde(untagged)]
+pub enum EnvOption {
+    String(String),
+    Value {
+        value: String,
+        #[serde(default)]
+        force: bool,
+        #[serde(default)]
+        relative: bool,
+    },
+}
+
+impl EnvOption {
+    /// Retrieve the value and canonicalize it relative to `config_parent` when [`EnvOption::Value::relative`] is set.
+    ///
+    /// `config_parent` is the directory containing `.cargo/config.toml` where this was parsed from.
+    pub fn resolve_value(&self, config_parent: impl AsRef<Path>) -> Result<Cow<'_, str>> {
+        Ok(match self {
+            Self::Value {
+                value,
+                relative: true,
+                force: _,
+            } => {
+                let value = config_parent.as_ref().join(value);
+                let value = dunce::canonicalize(&value)
+                    .with_context(|| format!("Failed to canonicalize `{}`", value.display()))?;
+                value
+                    .into_os_string()
+                    .into_string()
+                    .map_err(VarError::NotUnicode)?
+                    .into()
+            }
+            Self::String(value) | Self::Value { value, .. } => value.into(),
+        })
+    }
+}
+
+#[test]
+fn test_env_parsing() {
+    let toml = r#"
+[env]
+# Set ENV_VAR_NAME=value for any process run by Cargo
+ENV_VAR_NAME = "value"
+# Set even if already present in environment
+ENV_VAR_NAME_2 = { value = "value", force = true }
+# Value is relative to .cargo directory containing `config.toml`, make absolute
+ENV_VAR_NAME_3 = { value = "relative/path", relative = true }"#;
+
+    let mut env = BTreeMap::new();
+    env.insert(
+        "ENV_VAR_NAME".to_string(),
+        EnvOption::String("value".into()),
+    );
+    env.insert(
+        "ENV_VAR_NAME_2".to_string(),
+        EnvOption::Value {
+            value: "value".into(),
+            force: true,
+            relative: false,
+        },
+    );
+    env.insert(
+        "ENV_VAR_NAME_3".to_string(),
+        EnvOption::Value {
+            value: "relative/path".into(),
+            force: false,
+            relative: true,
+        },
+    );
+
+    assert_eq!(
+        toml::from_str::<Config>(toml),
+        Ok(Config {
+            build: None,
+            env: Some(env)
+        })
+    );
+}
+
+#[test]
+fn test_env_precedence_rules() {
+    let toml = r#"
+[env]
+CARGO_SUBCOMMAND_TEST_ENV_NOT_FORCED = "not forced"
+CARGO_SUBCOMMAND_TEST_ENV_FORCED = { value = "forced", force = true }"#;
+
+    let config = LocalizedConfig {
+        config: toml::from_str::<Config>(toml).unwrap(),
+        workspace: PathBuf::new(),
+    };
+
+    // Check if all values are propagated to the environment
+    config.set_env_vars().unwrap();
+
+    assert!(matches!(
+        std::env::var("CARGO_SUBCOMMAND_TEST_ENV_NOT_SET"),
+        Err(VarError::NotPresent)
+    ));
+    assert_eq!(
+        std::env::var("CARGO_SUBCOMMAND_TEST_ENV_NOT_FORCED").unwrap(),
+        "not forced"
+    );
+    assert_eq!(
+        std::env::var("CARGO_SUBCOMMAND_TEST_ENV_FORCED").unwrap(),
+        "forced"
+    );
+
+    // Set some environment values
+    std::env::set_var(
+        "CARGO_SUBCOMMAND_TEST_ENV_NOT_FORCED",
+        "not forced process environment value",
+    );
+    std::env::set_var(
+        "CARGO_SUBCOMMAND_TEST_ENV_FORCED",
+        "forced process environment value",
+    );
+
+    config.set_env_vars().unwrap();
+
+    assert_eq!(
+        std::env::var("CARGO_SUBCOMMAND_TEST_ENV_NOT_FORCED").unwrap(),
+        // Value remains what is set in the process environment,
+        // and is not overwritten by set_env_vars()
+        "not forced process environment value"
+    );
+    assert_eq!(
+        std::env::var("CARGO_SUBCOMMAND_TEST_ENV_FORCED").unwrap(),
+        // Value is overwritten thanks to force=true, despite
+        // also being set in the process environment
+        "forced"
+    );
+}
+
+#[test]
+fn test_env_canonicalization() {
+    use std::ffi::OsStr;
+
+    let toml = r#"
+[env]
+CARGO_SUBCOMMAND_TEST_ENV_SRC_DIR = { value = "src", force = true, relative = true }
+"#;
+
+    let config = LocalizedConfig {
+        config: toml::from_str::<Config>(toml).unwrap(),
+        workspace: PathBuf::new(),
+    };
+
+    config.set_env_vars().unwrap();
+
+    let path = std::env::var("CARGO_SUBCOMMAND_TEST_ENV_SRC_DIR")
+        .expect("Canonicalization for a known-to-exist ./src folder should not fail");
+    let path = PathBuf::from(path);
+    assert!(path.is_absolute());
+    assert!(path.is_dir());
+    assert_eq!(path.file_name(), Some(OsStr::new("src")));
+
+    let toml = r#"
+[env]
+CARGO_SUBCOMMAND_TEST_ENV_INEXISTENT_DIR = { value = "blahblahthisfolderdoesntexist", force = true, relative = true }
+"#;
+
+    let config = LocalizedConfig {
+        config: toml::from_str::<Config>(toml).unwrap(),
+        workspace: PathBuf::new(),
+    };
+
+    let e = config.set_env_vars().unwrap_err();
+
+    assert_eq!(
+        e.to_string(),
+        "Failed to canonicalize `blahblahthisfolderdoesntexist`"
+    );
+    assert_eq!(
+        e.root_cause().to_string(),
+        "No such file or directory (os error 2)"
+    );
+}

xbuild/src/cargo/mod.rs

@@ -10,7 +10,7 @@ mod utils;
 
 pub use artifact::{Artifact, CrateType};
 
-use self::config::Config;
+use self::config::LocalizedConfig;
 use self::manifest::Manifest;
 use crate::{CompileTarget, Opt};
 
@@ -74,11 +74,10 @@ impl Cargo {
 
         // TODO: Find, parse, and merge _all_ config files following the hierarchical structure:
         // https://doc.rust-lang.org/cargo/reference/config.html#hierarchical-structure
-        let config = Config::find_cargo_config_for_workspace(package_root)?;
-        // TODO: Import LocalizedConfig code from cargo-subcommand and propagate `[env]`
-        // if let Some(config) = &config {
-        //     config.set_env_vars().unwrap();
-        // }
+        let config = LocalizedConfig::find_cargo_config_for_workspace(package_root)?;
+        if let Some(config) = &config {
+            config.set_env_vars().unwrap();
+        }
 
         let target_dir = target_dir
             .or_else(|| {
@@ -101,7 +100,7 @@ impl Cargo {
                 .unwrap_or_else(|| &manifest_path)
                 .parent()
                 .unwrap()
-                .join(utils::get_target_dir_name(config.as_ref()).unwrap())
+                .join(utils::get_target_dir_name(config.as_deref()).unwrap())
         });
 
         Ok(Self {

xbuild/src/lib.rs

@@ -387,7 +387,7 @@ pub struct BuildTargetArgs {
     /// Build artifacts for target device. To find the device
     /// identifier of a connected device run `x devices`.
     #[clap(long, conflicts_with = "store")]
-    device: Option<Device>,
+    device: Option<String>,
     /// Build artifacts with format. Can be one of `aab`,
     /// `apk`, `appbundle`, `appdir`, `appimage`, `dmg`,
     /// `exe`, `ipa`, `msix`.
@@ -424,6 +424,9 @@ impl BuildTargetArgs {
             Some(Device::host())
         } else {
             self.device
+                .as_ref()
+                .map(|device| device.parse())
+                .transpose()?
         };
         let platform = if let Some(platform) = self.platform {
             platform