bootstrap: Support passing --timings to cargo

Useful for optimizing the sequencing of the compiler's own build.

Author: joshtriplett

src/bootstrap/src/core/builder/cargo.rs

@@ -499,6 +499,10 @@ impl Builder<'_> {
             build_stamp::clear_if_dirty(self, &out_dir, &backend);
         }
 
+        if self.config.cmd.timings() {
+            cargo.arg("--timings");
+        }
+
         if cmd_kind == Kind::Doc {
             let my_out = match mode {
                 // This is the intended out directory for compiler documentation.

src/bootstrap/src/core/builder/mod.rs

@@ -1267,7 +1267,7 @@ impl<'a> Builder<'a> {
     pub fn new(build: &Build) -> Builder<'_> {
         let paths = &build.config.paths;
         let (kind, paths) = match build.config.cmd {
-            Subcommand::Build => (Kind::Build, &paths[..]),
+            Subcommand::Build { .. } => (Kind::Build, &paths[..]),
             Subcommand::Check { .. } => (Kind::Check, &paths[..]),
             Subcommand::Clippy { .. } => (Kind::Clippy, &paths[..]),
             Subcommand::Fix => (Kind::Fix, &paths[..]),

src/bootstrap/src/core/config/config.rs

@@ -1342,7 +1342,7 @@ impl Config {
             Subcommand::Doc { .. } => {
                 flags_stage.or(build_doc_stage).unwrap_or(if download_rustc { 2 } else { 1 })
             }
-            Subcommand::Build => {
+            Subcommand::Build { .. } => {
                 flags_stage.or(build_build_stage).unwrap_or(if download_rustc { 2 } else { 1 })
             }
             Subcommand::Test { .. } | Subcommand::Miri { .. } => {
@@ -1363,7 +1363,7 @@ impl Config {
 
         // Now check that the selected stage makes sense, and if not, print a warning and end
         match (config.stage, &config.cmd) {
-            (0, Subcommand::Build) => {
+            (0, Subcommand::Build { .. }) => {
                 eprintln!("ERROR: cannot build anything on stage 0. Use at least stage 1.");
                 exit!(1);
             }
@@ -1392,7 +1392,7 @@ impl Config {
                 Subcommand::Test { .. }
                 | Subcommand::Miri { .. }
                 | Subcommand::Doc { .. }
-                | Subcommand::Build
+                | Subcommand::Build { .. }
                 | Subcommand::Bench { .. }
                 | Subcommand::Dist
                 | Subcommand::Install => {

src/bootstrap/src/core/config/flags.rs

@@ -241,7 +241,7 @@ fn normalize_args(args: &[String]) -> Vec<String> {
     it.collect()
 }
 
-#[derive(Debug, Clone, Default, clap::Subcommand)]
+#[derive(Debug, Clone, clap::Subcommand)]
 pub enum Subcommand {
     #[command(aliases = ["b"], long_about = "\n
     Arguments:
@@ -256,8 +256,11 @@ pub enum Subcommand {
             ./x.py build --stage 0
             ./x.py build ")]
     /// Compile either the compiler or libraries
-    #[default]
-    Build,
+    Build {
+        #[arg(long)]
+        /// Pass `--timings` to Cargo to get crate build timings
+        timings: bool,
+    },
     #[command(aliases = ["c"], long_about = "\n
     Arguments:
         This subcommand accepts a number of paths to directories to the crates
@@ -269,6 +272,9 @@ pub enum Subcommand {
         #[arg(long)]
         /// Check all targets
         all_targets: bool,
+        #[arg(long)]
+        /// Pass `--timings` to Cargo to get crate build timings
+        timings: bool,
     },
     /// Run Clippy (uses rustup/cargo-installed clippy binary)
     #[command(long_about = "\n
@@ -494,11 +500,17 @@ Arguments:
     Perf(PerfArgs),
 }
 
+impl Default for Subcommand {
+    fn default() -> Self {
+        Subcommand::Build { timings: false }
+    }
+}
+
 impl Subcommand {
     pub fn kind(&self) -> Kind {
         match self {
             Subcommand::Bench { .. } => Kind::Bench,
-            Subcommand::Build => Kind::Build,
+            Subcommand::Build { .. } => Kind::Build,
             Subcommand::Check { .. } => Kind::Check,
             Subcommand::Clippy { .. } => Kind::Clippy,
             Subcommand::Doc { .. } => Kind::Doc,
@@ -626,6 +638,13 @@ impl Subcommand {
         }
     }
 
+    pub fn timings(&self) -> bool {
+        match *self {
+            Subcommand::Build { timings, .. } | Subcommand::Check { timings, .. } => timings,
+            _ => false,
+        }
+    }
+
     pub fn vendor_versioned_dirs(&self) -> bool {
         match *self {
             Subcommand::Vendor { versioned_dirs, .. } => versioned_dirs,