fix(env): dont track envs set by cargo in dep-info file

This patch is quite hacky since the "set-by-Cargo" env vars are
hardcoded. However, not all environment variables set by Cargo are
statically known. To prevent the actual environment variables applied to
rustc invocation get out of sync from what we hard-code, a debug time
assertion is put to help discover missing environment variables earlier.

src/cargo/core/compiler/compilation.rs

@@ -1,8 +1,11 @@
 //! Type definitions for the result of a compilation.
 
-use std::collections::{BTreeSet, HashMap};
+use std::collections::BTreeSet;
+use std::collections::HashMap;
+use std::collections::HashSet;
 use std::ffi::{OsStr, OsString};
 use std::path::PathBuf;
+use std::sync::LazyLock;
 
 use cargo_platform::CfgExpr;
 use cargo_util::{paths, ProcessBuilder};
@@ -529,3 +532,88 @@ fn target_linker(bcx: &BuildContext<'_, '_>, kind: CompileKind) -> CargoResult<O
     }
     Ok(matching_linker.map(|(_k, linker)| linker.val.clone().resolve_program(bcx.gctx)))
 }
+
+/// This tracks environment variables Cargo sets to rustc when building a crate.
+///
+/// This only inclues variables with statically known keys.
+/// For environment variable keys that vary like `CARG_BIN_EXE_<name>` or
+/// `-Zbindeps` related env vars, we compare only their prefixes to determine
+/// if they are internal.
+/// See [`is_env_set_by_cargo`] and
+/// <https://doc.rust-lang.org/nightly/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates>.
+static ENV_VARS_SET_FOR_CRATES: LazyLock<HashSet<&'static str>> = LazyLock::new(|| {
+    HashSet::from_iter([
+        crate::CARGO_ENV,
+        "CARGO_MANIFEST_DIR",
+        "CARGO_MANIFEST_PATH",
+        "CARGO_PKG_VERSION",
+        "CARGO_PKG_VERSION_MAJOR",
+        "CARGO_PKG_VERSION_MINOR",
+        "CARGO_PKG_VERSION_PATCH",
+        "CARGO_PKG_VERSION_PRE",
+        "CARGO_PKG_AUTHORS",
+        "CARGO_PKG_NAME",
+        "CARGO_PKG_DESCRIPTION",
+        "CARGO_PKG_HOMEPAGE",
+        "CARGO_PKG_REPOSITORY",
+        "CARGO_PKG_LICENSE",
+        "CARGO_PKG_LICENSE_FILE",
+        "CARGO_PKG_RUST_VERSION",
+        "CARGO_PKG_README",
+        "CARGO_CRATE_NAME",
+        "CARGO_BIN_NAME",
+        "OUT_DIR",
+        "CARGO_PRIMARY_PACKAGE",
+        "CARGO_TARGET_TMPDIR",
+        paths::dylib_path_envvar(),
+    ])
+});
+
+/// Asserts if the given env vars are controlled by Cargo.
+///
+/// This is only for reminding Cargo developer to keep newly added environment
+/// variables in sync with [`ENV_VARS_SET_FOR_CRATES`].
+#[cfg(debug_assertions)]
+pub(crate) fn assert_only_envs_set_by_cargo<'a>(
+    keys: impl Iterator<Item = impl AsRef<str>>,
+    env_config: &HashMap<String, OsString>,
+) {
+    for key in keys {
+        let key = key.as_ref();
+        // When running Cargo's test suite,
+        // we're fine if it is from the `[env]` table
+        if env_config.contains_key(key) {
+            continue;
+        }
+        assert!(
+            is_env_set_by_cargo(key),
+            "`{key}` is not tracked as an environment variable set by Cargo\n\
+            Add it to `ENV_VARS_SET_FOR_CRATES` if you intend to introduce a new one"
+        );
+    }
+}
+
+/// True if the given env var is controlled or set by Cargo.
+/// See [`ENV_VARS_SET_FOR_CRATES`].
+pub(crate) fn is_env_set_by_cargo(key: &str) -> bool {
+    ENV_VARS_SET_FOR_CRATES.contains(key)
+        || key.starts_with("CARGO_BIN_EXE_")
+        || key.starts_with("__CARGO") // internal/test-only envs
+        || key == "RUSTC_BOOTSTRAP" // for -Zbuild-std
+        || is_artifact_dep_env_vars(key)
+}
+
+/// Whether an env var is set because of `-Zbindeps`.
+fn is_artifact_dep_env_vars(key: &str) -> bool {
+    let Some(key) = key.strip_prefix("CARGO_") else {
+        return false;
+    };
+    let Some(key) = key
+        .strip_prefix("BIN_")
+        .or_else(|| key.strip_prefix("CDYLIB_"))
+        .or_else(|| key.strip_prefix("STATICLIB_"))
+    else {
+        return false;
+    };
+    key.starts_with("FILE_") || key.starts_with("DIR_")
+}

src/cargo/core/compiler/fingerprint/dep_info.rs

@@ -19,6 +19,7 @@ use cargo_util::paths;
 use cargo_util::ProcessBuilder;
 use cargo_util::Sha256;
 
+use crate::core::compiler::is_env_set_by_cargo;
 use crate::CargoResult;
 use crate::CARGO_ENV;
 
@@ -334,7 +335,13 @@ pub fn translate_dep_info(
     //
     // For cargo#13280, We trace env vars that are defined in the `[env]` config table.
     on_disk_info.env.retain(|(key, _)| {
-        env_config.contains_key(key) || !rustc_cmd.get_envs().contains_key(key) || key == CARGO_ENV
+        if key == CARGO_ENV {
+            return true;
+        }
+        if !rustc_cmd.get_envs().contains_key(key) {
+            return true;
+        }
+        env_config.contains_key(key) && !is_env_set_by_cargo(key)
     });
 
     let serialize_path = |file| {

src/cargo/core/compiler/mod.rs

@@ -74,6 +74,7 @@ pub use self::build_context::{
 };
 use self::build_plan::BuildPlan;
 pub use self::build_runner::{BuildRunner, Metadata};
+pub(crate) use self::compilation::is_env_set_by_cargo;
 pub use self::compilation::{Compilation, Doctest, UnitOutput};
 pub use self::compile_kind::{CompileKind, CompileTarget};
 pub use self::crate_type::CrateType;
@@ -334,6 +335,10 @@ fn rustc(
         output_options.show_diagnostics = false;
     }
     let env_config = Arc::clone(build_runner.bcx.gctx.env_config()?);
+
+    #[cfg(debug_assertions)]
+    compilation::assert_only_envs_set_by_cargo(rustc.get_envs().keys(), &env_config);
+
     return Ok(Work::new(move |state| {
         // Artifacts are in a different location than typical units,
         // hence we must assure the crate- and target-dependent

tests/testsuite/cargo_env_config.rs

@@ -460,8 +460,10 @@ fn override_env_set_by_cargo() {
         .build();
 
     let args = [
-        "--config", "env.CARGO_MANIFEST_DIR='Sauron'",
-        "--config", "env.CARGO_PKG_NAME='Saruman'",
+        "--config",
+        "env.CARGO_MANIFEST_DIR='Sauron'",
+        "--config",
+        "env.CARGO_PKG_NAME='Saruman'",
     ];
 
     p.cargo("run")
@@ -488,7 +490,6 @@ foo
 
 "#]])
         .with_stderr_data(str![[r#"
-[COMPILING] foo v0.5.0 ([ROOT]/foo)
 [FINISHED] `dev` profile [unoptimized + debuginfo] target(s) in [ELAPSED]s
 [RUNNING] `target/debug/foo[EXE]`