config: Deny CARGO_HOME in [env] table (fixes #11590)

Author: basile-henry

src/cargo/util/config/mod.rs

@@ -1685,8 +1685,15 @@ impl Config {
     }
 
     pub fn env_config(&self) -> CargoResult<&EnvConfig> {
-        self.env_config
-            .try_borrow_with(|| self.get::<EnvConfig>("env"))
+        let env_config = self
+            .env_config
+            .try_borrow_with(|| self.get::<EnvConfig>("env"))?;
+
+        if env_config.get("CARGO_HOME").is_some() {
+            bail!("`CARGO_HOME` environment variable should be not be set in `.cargo/config` via `env.CARGO_HOME` as cargo does not use this value directly (only recursive calls to cargo would)");
+        }
+
+        Ok(env_config)
     }
 
     /// This is used to validate the `term` table has valid syntax.

tests/testsuite/cargo_env_config.rs

@@ -57,6 +57,32 @@ fn env_invalid() {
         .run();
 }
 
+#[cargo_test]
+fn env_no_cargo_home() {
+    let p = project()
+        .file("Cargo.toml", &basic_bin_manifest("foo"))
+        .file(
+            "src/main.rs",
+            r#"
+        fn main() {
+        }
+        "#,
+        )
+        .file(
+            ".cargo/config",
+            r#"
+                [env]
+                CARGO_HOME = "/"
+            "#,
+        )
+        .build();
+
+    p.cargo("build")
+        .with_status(101)
+        .with_stderr_contains("[..]`CARGO_HOME` environment variable should be not be set in `.cargo/config` via `env.CARGO_HOME` as cargo does not use this value directly (only recursive calls to cargo would)")
+        .run();
+}
+
 #[cargo_test]
 fn env_force() {
     let p = project()