Auto merge of #4990 - Eh2406:Zno-index-update, r=alexcrichton

add a -Z no-index-update for crater and benchmarking

This is a fix for #3479

src/cargo/core/features.rs

@@ -233,6 +233,7 @@ pub struct CliUnstable {
     pub print_im_a_teapot: bool,
     pub unstable_options: bool,
     pub offline: bool,
+    pub no_index_update: bool,
 }
 
 impl CliUnstable {
@@ -264,6 +265,7 @@ impl CliUnstable {
             "print-im-a-teapot" => self.print_im_a_teapot = parse_bool(v)?,
             "unstable-options" => self.unstable_options = true,
             "offline" => self.offline = true,
+            "no-index-update" => self.no_index_update = true,
             _ => bail!("unknown `-Z` flag specified: {}", k),
         }
 

src/cargo/sources/registry/remote.rs

@@ -156,6 +156,9 @@ impl<'cfg> RegistryData for RemoteRegistry<'cfg> {
         if self.config.cli_unstable().offline {
             return Ok(());
         }
+        if self.config.cli_unstable().no_index_update {
+            return Ok(());
+        }
 
         // Ensure that we'll actually be able to acquire an HTTP handle later on
         // once we start trying to download crates. This will weed out any

tests/generate-lockfile.rs

@@ -74,6 +74,31 @@ fn adding_and_removing_packages() {
     assert_eq!(lock1, lock4);
 }
 
+#[test]
+fn no_index_update() {
+    use cargotest::ChannelChanger;
+    let p = project("foo")
+        .file("Cargo.toml", r#"
+            [package]
+            name = "foo"
+            authors = []
+            version = "0.0.1"
+
+            [dependencies]
+            serde = "1.0"
+        "#)
+        .file("src/main.rs", "fn main() {}")
+        .build();
+
+    assert_that(p.cargo("generate-lockfile"),
+                execs().with_status(0).with_stdout("")
+                    .with_stderr_contains("    Updating registry `https://github.com/rust-lang/crates.io-index`"));
+
+    assert_that(p.cargo("generate-lockfile").masquerade_as_nightly_cargo().arg("-Zno-index-update"),
+                execs().with_status(0).with_stdout("")
+                    .with_stderr_does_not_contain("    Updating registry `https://github.com/rust-lang/crates.io-index`"));
+}
+
 #[test]
 fn preserve_metadata() {
     let p = project("foo")