Allow to generate lockfile without registry update

src/bin/generate_lockfile.rs

@@ -13,6 +13,7 @@ pub struct Options {
     flag_color: Option<String>,
     flag_frozen: bool,
     flag_locked: bool,
+    flag_offline: bool,
 }
 
 pub const USAGE: &'static str = "
@@ -29,6 +30,8 @@ Options:
     --color WHEN             Coloring: auto, always, never
     --frozen                 Require Cargo.lock and cache are up to date
     --locked                 Require Cargo.lock is up to date
+    --offline                Do not download crates.io registry and use
+                             a potentially stale local copy
 ";
 
 pub fn execute(options: Options, config: &Config) -> CliResult {
@@ -38,6 +41,9 @@ pub fn execute(options: Options, config: &Config) -> CliResult {
                      &options.flag_color,
                      options.flag_frozen,
                      options.flag_locked)?;
+    if options.flag_offline {
+        config.disable_registry_update();
+    }
     let root = find_root_manifest_for_wd(options.flag_manifest_path, config.cwd())?;
 
     let ws = Workspace::new(&root, config)?;

src/cargo/sources/registry/remote.rs

@@ -60,7 +60,9 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
         //
         // This way if there's a problem the error gets printed before we even
         // hit the index, which may not actually read this configuration.
-        ops::http_handle(self.config)?;
+        if self.config.registry_update_allowed() {
+            ops::http_handle(self.config)?;
+        }
 
         // Then we actually update the index
         self.index_path.create_dir()?;
@@ -69,10 +71,19 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
                                            "the registry index")?;
         let path = lock.path().parent().unwrap();
 
+        let existing_repo = git2::Repository::open(path);
+        if !self.config.registry_update_allowed() {
+            return if let Err(e) = existing_repo {
+                Err(e.into())
+            } else {
+                Ok(())
+            }
+        }
+
         self.config.shell().status("Updating",
              format!("registry `{}`", self.source_id.url()))?;
 
-        let repo = git2::Repository::open(path).or_else(|_| {
+        let repo = existing_repo.or_else(|_| {
             let _ = lock.remove_siblings();
             git2::Repository::init(path)
         })?;

src/cargo/util/config.rs

@@ -33,6 +33,7 @@ pub struct Config {
     extra_verbose: Cell<bool>,
     frozen: Cell<bool>,
     locked: Cell<bool>,
+    disable_registry_update: Cell<bool>,
 }
 
 impl Config {
@@ -50,6 +51,7 @@ impl Config {
             extra_verbose: Cell::new(false),
             frozen: Cell::new(false),
             locked: Cell::new(false),
+            disable_registry_update: Cell::new(false),
         }
     }
 
@@ -377,6 +379,14 @@ impl Config {
         !self.frozen.get() && !self.locked.get()
     }
 
+    pub fn registry_update_allowed(&self) -> bool {
+        !self.disable_registry_update.get()
+    }
+
+    pub fn disable_registry_update(&self) {
+        self.disable_registry_update.set(true)
+    }
+
     fn load_values(&self) -> CargoResult<HashMap<String, ConfigValue>> {
         let mut cfg = CV::Table(HashMap::new(), PathBuf::from("."));