make a helper function

Author: Eh2406

src/cargo/core/compiler/custom_build.rs

@@ -332,14 +332,7 @@ fn build_work<'a, 'cfg>(cx: &mut Context<'a, 'cfg>, unit: &Unit<'a>) -> CargoRes
             state.build_plan(invocation_name, cmd.clone(), Arc::new(Vec::new()));
         } else {
             state.running(&cmd);
-            // `invoked.timestamp` is used to get `FileTime::from_system_time(SystemTime::now());`
-            // using the exact clock that this file system is using.
-            let timestamp = output_file.with_file_name("invoked.timestamp");
-            paths::write(
-                &timestamp,
-                b"This file has an mtime of when this build-script was started.",
-            )?;
-            let timestamp = paths::mtime(&timestamp)?;
+            let timestamp = paths::get_current_filesystem_time(&output_file)?;
             let output = if extra_verbose {
                 let prefix = format!("[{} {}] ", id.name(), id.version());
                 state.capture_output(&cmd, Some(prefix), true)

src/cargo/core/compiler/mod.rs

@@ -292,14 +292,7 @@ fn rustc<'a, 'cfg>(
         }
 
         state.running(&rustc);
-        // `invoked.timestamp` is used to get `FileTime::from_system_time(SystemTime::now());`
-        // using the exact clock that this file system is using.
-        let timestamp = dep_info_loc.with_file_name("invoked.timestamp");
-        paths::write(
-            &timestamp,
-            b"This file has an mtime of when rustc was started.",
-        )?;
-        let timestamp = paths::mtime(&timestamp)?;
+        let timestamp = paths::get_current_filesystem_time(&dep_info_loc)?;
         if json_messages {
             exec.exec_json(
                 rustc,

src/cargo/util/paths.rs

@@ -197,6 +197,18 @@ pub fn mtime(path: &Path) -> CargoResult<FileTime> {
     Ok(FileTime::from_last_modification_time(&meta))
 }
 
+/// get `FileTime::from_system_time(SystemTime::now());` using the exact clock that this file system is using.
+pub fn get_current_filesystem_time(path: &Path) -> CargoResult<FileTime> {
+    // note that if `FileTime::from_system_time(SystemTime::now());` is determined to be sufficient,
+    // then this can be removed.
+    let timestamp = path.with_file_name("invoked.timestamp");
+    write(
+        &timestamp,
+        b"This file has an mtime of when this was started.",
+    )?;
+    Ok(mtime(&timestamp)?)
+}
+
 #[cfg(unix)]
 pub fn path2bytes(path: &Path) -> CargoResult<&[u8]> {
     use std::os::unix::prelude::*;