Add -Z advanced-env feature flag.

src/cargo/core/features.rs

@@ -308,6 +308,7 @@ pub struct CliUnstable {
     pub avoid_dev_deps: bool,
     pub minimal_versions: bool,
     pub package_features: bool,
+    pub advanced_env: bool,
 }
 
 impl CliUnstable {
@@ -342,6 +343,7 @@ impl CliUnstable {
             "avoid-dev-deps" => self.avoid_dev_deps = true,
             "minimal-versions" => self.minimal_versions = true,
             "package-features" => self.package_features = true,
+            "advanced-env" => self.advanced_env = true,
             _ => bail!("unknown `-Z` flag specified: {}", k),
         }
 

src/cargo/util/config.rs

@@ -965,7 +965,10 @@ impl<'de, 'config> de::Deserializer<'de> for Deserializer<'config> {
                 visitor.visit_bool(v.parse().unwrap())
             } else if let Ok(v) = v.parse::<i64>() {
                 visitor.visit_i64(v)
-            } else if v.starts_with("[") && v.ends_with("]") {
+            } else if self.config.cli_unstable().advanced_env
+                && v.starts_with("[")
+                && v.ends_with("]")
+            {
                 visitor.visit_seq(ConfigSeqAccess::new(self.config, self.key.clone())?)
             } else {
                 visitor.visit_string(v.clone())
@@ -1121,6 +1124,7 @@ impl<'config> ConfigMapAccess<'config> {
                 set.insert(ConfigKeyPart::CasePart(key));
             }
         }
+        if config.cli_unstable().advanced_env {
             // CARGO_PROFILE_DEV_OVERRIDES_
             let env_pattern = format!("{}_", key.to_env());
             for env_key in config.env.keys() {
@@ -1133,6 +1137,7 @@ impl<'config> ConfigMapAccess<'config> {
                     set.insert(ConfigKeyPart::CasePart(part.to_string()));
                 }
             }
+        }
         Ok(ConfigMapAccess {
             config,
             key,
@@ -1214,6 +1219,7 @@ impl ConfigSeqAccess {
             }
         }
 
+        if config.cli_unstable().advanced_env {
             // Parse an environment string as a TOML array.
             let env_key = key.to_env();
             let def = Definition::Environment(env_key.clone());
@@ -1247,6 +1253,7 @@ impl ConfigSeqAccess {
                     res.push((s.to_string(), def.clone()));
                 }
             }
+        }
         Ok(ConfigSeqAccess {
             list_iter: res.into_iter(),
         })

tests/testsuite/config.rs

@@ -55,6 +55,15 @@ fn new_config(env: &[(&str, &str)]) -> Config {
         .collect();
     let mut config = Config::new(shell, cwd, homedir);
     config.set_env(env);
+    config.configure(
+        0,
+        None,
+        &None,
+        false,
+        false,
+        &None,
+        &["advanced-env".into()],
+    ).unwrap();
     config
 }