set mtime_on_use from config or ENV

Author: Eh2406

src/cargo/core/features.rs

@@ -386,6 +386,7 @@ impl CliUnstable {
             "advanced-env" => self.advanced_env = true,
             "config-profile" => self.config_profile = true,
             "dual-proc-macros" => self.dual_proc_macros = true,
+            // can also be set in .cargo/config or with and ENV
             "mtime-on-use" => self.mtime_on_use = true,
             "install-upgrade" => self.install_upgrade = true,
             "cache-messages" => self.cache_messages = true,

src/cargo/util/config.rs

@@ -23,7 +23,7 @@ use url::Url;
 use self::ConfigValue as CV;
 use crate::core::profiles::ConfigProfiles;
 use crate::core::shell::Verbosity;
-use crate::core::{CliUnstable, Shell, SourceId, Workspace};
+use crate::core::{nightly_features_allowed, CliUnstable, Shell, SourceId, Workspace};
 use crate::ops;
 use crate::util::errors::{self, internal, CargoResult, CargoResultExt};
 use crate::util::toml as cargo_toml;
@@ -626,6 +626,12 @@ impl Config {
         self.target_dir = cli_target_dir;
         self.cli_flags.parse(unstable_flags)?;
 
+        if nightly_features_allowed() {
+            if let Some(val) = self.get_bool("unstable.mtime_on_use")?.map(|t| t.val) {
+                self.cli_flags.mtime_on_use |= val;
+            }
+        }
+
         Ok(())
     }