Pass cargo configuration flags to docker.

Ensures the following flags are passed to docker:
- BROWSER
- CARGO_BUILD_DEP_INFO_BASEDIR
- CARGO_BUILD_INCREMENTAL
- CARGO_BUILD_JOBS
- CARGO_BUILD_RUSTDOCFLAGS
- CARGO_BUILD_RUSTFLAGS
- CARGO_CACHE_RUSTC_INFO
- CARGO_CACHE_RUSTC_INFO
- CARGO_FUTURE_INCOMPAT_REPORT_FREQUENCY
- CARGO_HTTP_CAINFO
- CARGO_HTTP_CHECK_REVOKE
- CARGO_HTTP_DEBUG
- CARGO_HTTP_LOW_SPEED_LIMIT
- CARGO_HTTP_MULTIPLEXING
- CARGO_HTTP_PROXY
- CARGO_HTTP_SSL_VERSION
- CARGO_HTTP_TIMEOUT
- CARGO_HTTP_USER_AGENT
- CARGO_INCREMENTAL
- CARGO_INCREMENTAL
- CARGO_NET_GIT_FETCH_WITH_CLI
- CARGO_NET_OFFLINE
- CARGO_NET_RETRY
- HTTP_TIMEOUT
- HTTPS_PROXY
- RUSTDOCFLAGS
- RUSTFLAGS
- TERM

These are always correct, since these configure how `cargo` behavior is
supposed to work, but don't rely on any paths on the host filesystem. We also have some future-proofing, since we accept anything starting with `CARGO_` except the following variables:

It also ensures the following overridden environment variables are not passed:
- CARGO_HOME
- CARGO_TARGET_DIR
- CARGO_BUILD_TARGET_DIR

And it ensures the following not-yet-supported environment variables are not passed:
- CARGO_BUILD_RUSTC
- CARGO_BUILD_RUSTC_WRAPPER
- CARGO_BUILD_RUSTC_WORKSPACE_WRAPPER
- CARGO_BUILD_RUSTDOC

CHANGELOG.md

@@ -7,6 +7,9 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased] - ReleaseDate
 
+### Changed
+- #869 - ensure cargo configuration environment variable flags are passed to the docker container.
+
 ### Fixed
 
 - #867 - fixed parsing of `build.env,passthrough` config values.

src/docker/shared.rs

@@ -221,6 +221,40 @@ pub(crate) fn cargo_safe_command(uses_xargo: bool) -> SafeCommand {
     }
 }
 
+fn add_cargo_configuration_envvars(docker: &mut Command) {
+    let non_cargo_prefix = &[
+        "http_proxy",
+        "TERM",
+        "RUSTDOCFLAGS",
+        "RUSTFLAGS",
+        "BROWSER",
+        "HTTPS_PROXY",
+        "HTTP_TIMEOUT",
+        "https_proxy",
+    ];
+    let cargo_prefix_skip = &[
+        "CARGO_HOME",
+        "CARGO_TARGET_DIR",
+        "CARGO_BUILD_TARGET_DIR",
+        "CARGO_BUILD_RUSTC",
+        "CARGO_BUILD_RUSTC_WRAPPER",
+        "CARGO_BUILD_RUSTC_WORKSPACE_WRAPPER",
+        "CARGO_BUILD_RUSTDOC",
+    ];
+    let is_cargo_passthrough = |key: &str| -> bool {
+        non_cargo_prefix.contains(&key)
+            || key.starts_with("CARGO_") && !cargo_prefix_skip.contains(&key)
+    };
+
+    // also need to accept any additional flags used to configure
+    // cargo, but only pass what's actually present.
+    for (key, _) in env::vars() {
+        if is_cargo_passthrough(&key) {
+            docker.args(&["-e", &key]);
+        }
+    }
+}
+
 pub(crate) fn mount(docker: &mut Command, val: &Path, prefix: &str) -> Result<String> {
     let host_path = file::canonicalize(val)?;
     let mount_path = canonicalize_mount_path(&host_path)?;
@@ -248,6 +282,7 @@ pub(crate) fn docker_envvars(docker: &mut Command, config: &Config, target: &Tar
         .args(&["-e", "CARGO_HOME=/cargo"])
         .args(&["-e", "CARGO_TARGET_DIR=/target"])
         .args(&["-e", &cross_runner]);
+    add_cargo_configuration_envvars(docker);
 
     if let Some(username) = id::username().unwrap() {
         docker.args(&["-e", &format!("USER={username}")]);