Add --compile-time-deps argument for x check

This reduces the amount of time it takes to do the x check for
rust-analyzer analysis from 12m16s to 3m34s when the bootstrap compiler
is already downloaded.

Author: bjorn3

src/bootstrap/src/core/build_steps/check.rs

@@ -47,6 +47,11 @@ impl Step for Std {
     }
 
     fn make_run(run: RunConfig<'_>) {
+        if run.builder.config.compile_time_deps {
+            // libstd doesn't have any important build scripts and can't have any proc macros
+            return;
+        }
+
         let crates = std_crates_for_run_make(&run);
         run.builder.ensure(Std {
             build_compiler: prepare_compiler_for_check(run.builder, run.target, Mode::Std),
@@ -250,6 +255,13 @@ fn prepare_compiler_for_check(
     match mode {
         Mode::ToolBootstrap => builder.compiler(0, host),
         Mode::ToolStd => {
+            if builder.config.compile_time_deps {
+                // When --compile-time-deps is passed, we can't use any rustc
+                // other than the bootstrap compiler. Luckily build scripts and
+                // proc macros for tools are unlikely to need nightly.
+                return builder.compiler(0, host);
+            }
+
             // These tools require the local standard library to be checked
             let build_compiler = builder.compiler(builder.top_stage, host);
 

src/bootstrap/src/core/build_steps/compile.rs

@@ -2542,6 +2542,11 @@ pub fn stream_cargo(
     }
     cmd.arg("--message-format").arg(message_format);
 
+    if builder.config.compile_time_deps {
+        cmd.arg("-Zunstable-options");
+        cmd.arg("--compile-time-deps");
+    }
+
     for arg in tail_args {
         cmd.arg(arg);
     }

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

@@ -110,6 +110,7 @@ pub struct Config {
     pub include_default_paths: bool,
     pub rustc_error_format: Option<String>,
     pub json_output: bool,
+    pub compile_time_deps: bool,
     pub test_compare_mode: bool,
     pub color: Color,
     pub patch_binaries_for_nix: Option<bool>,
@@ -421,6 +422,7 @@ impl Config {
             jobs: flags_jobs,
             warnings: flags_warnings,
             json_output: flags_json_output,
+            compile_time_deps: flags_compile_time_deps,
             color: flags_color,
             bypass_bootstrap_lock: flags_bypass_bootstrap_lock,
             rust_profile_generate: flags_rust_profile_generate,
@@ -468,6 +470,7 @@ impl Config {
         config.include_default_paths = flags_include_default_paths;
         config.rustc_error_format = flags_rustc_error_format;
         config.json_output = flags_json_output;
+        config.compile_time_deps = flags_compile_time_deps;
         config.on_fail = flags_on_fail;
         config.cmd = flags_cmd;
         config.incremental = flags_incremental;
@@ -1064,6 +1067,13 @@ impl Config {
             _ => {}
         }
 
+        if config.compile_time_deps && !matches!(config.cmd, Subcommand::Check { .. }) {
+            eprintln!(
+                "WARNING: Can't use --compile-time-deps with any subcommand other than check."
+            );
+            exit!(1);
+        }
+
         // CI should always run stage 2 builds, unless it specifically states otherwise
         #[cfg(not(test))]
         if flags_stage.is_none() && config.is_running_on_ci {

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

@@ -132,6 +132,9 @@ pub struct Flags {
     #[arg(global = true, long)]
     /// use message-format=json
     pub json_output: bool,
+    #[arg(global = true, long)]
+    /// use --compile-time-deps
+    pub compile_time_deps: bool,
 
     #[arg(global = true, long, value_name = "STYLE")]
     #[arg(value_enum, default_value_t = Color::Auto)]

src/etc/rust_analyzer_eglot.el

@@ -23,7 +23,8 @@
                                                   :overrideCommand ["python3"
                                                                     "x.py"
                                                                     "check"
-                                                                    "--json-output"])
+                                                                    "--json-output"
+                                                                    "--compile-time-deps"])]
                                         :sysrootSrc "./library"
                                         :extraEnv (:RUSTC_BOOTSTRAP "1"))
                  :rustc ( :source "./Cargo.toml" )))))))

src/etc/rust_analyzer_helix.toml

@@ -59,4 +59,5 @@ overrideCommand = [
     "--json-output",
     "--build-dir",
     "build/rust-analyzer",
+    "--compile-time-deps"
 ]

src/etc/rust_analyzer_settings.json

@@ -27,7 +27,8 @@
         "python3",
         "x.py",
         "check",
-        "--json-output"
+        "--json-output",
+        "--compile-time-deps"
     ],
     "rust-analyzer.cargo.sysrootSrc": "./library",
     "rust-analyzer.rustc.source": "./Cargo.toml",

src/etc/rust_analyzer_zed.json

@@ -7,7 +7,7 @@
             "enable": true,
             "invocationLocation": "root",
             "invocationStrategy": "once",
-            "overrideCommand": ["python3", "x.py", "check", "--json-output"]
+            "overrideCommand": ["python3", "x.py", "check", "--json-output", "--compile-time-deps"]
           },
           "extraEnv": {
             "RUSTC_BOOTSTRAP": "1"