Prepare dependencies without locking Cargo.lock

This doesn't pass --locked to Cargo, as that can interfere with upgrading the
lockfile format and cause spurious failures on Crater (since generate-lockfile,
which will get run in this case, will cause dependencies to get upgraded when
this isn't actually necessary). We would always regenerate the lockfile from
scratch if it was needed at all, so this isn't really changing anything behavior
wise.

Author: Mark-Simulacrum

src/prepare.rs

@@ -141,24 +141,19 @@ impl<'a> Prepare<'a> {
     }
 
     fn fetch_deps(&mut self) -> Result<(), Error> {
-        let mut outdated_lockfile = false;
         let mut missing_deps = false;
         let res = Command::new(self.workspace, self.toolchain.cargo())
-            .args(&["fetch", "--locked", "--manifest-path", "Cargo.toml"])
+            .args(&["fetch", "--manifest-path", "Cargo.toml"])
             .cd(&self.source_dir)
             .process_lines(&mut |line, _| {
-                if line.ends_with(
-                    "Cargo.lock needs to be updated but --locked was passed to prevent this",
-                ) {
-                    outdated_lockfile = true;
-                } else if line.contains("failed to load source for dependency") {
+                if line.contains("failed to load source for dependency") {
                     missing_deps = true;
                 }
             })
             .run();
         match res {
             Ok(_) => Ok(()),
-            Err(_) if outdated_lockfile && !self.lockfile_captured => {
+            Err(_) if !self.lockfile_captured => {
                 info!("the lockfile is outdated, regenerating it");
                 // Force-update the lockfile and recursively call this function to fetch
                 // dependencies again.