Merge pull request rust-lang#20047 from ShoyuVanilla/comp-time-deps

internal: Utilize `cargo check --compile-time-deps`

Author: Veykril

src/tools/rust-analyzer/crates/project-model/src/build_dependencies.rs

@@ -20,7 +20,9 @@ use toolchain::Tool;
 
 use crate::{
     CargoConfig, CargoFeatures, CargoWorkspace, InvocationStrategy, ManifestPath, Package, Sysroot,
-    TargetKind, utf8_stdout,
+    TargetKind,
+    toolchain_info::{QueryConfig, version},
+    utf8_stdout,
 };
 
 /// Output of the build script and proc-macro building steps for a workspace.
@@ -446,10 +448,30 @@ impl WorkspaceBuildScripts {
             }
         };
 
-        if config.wrap_rustc_in_build_scripts {
+        // If [`--compile-time-deps` flag](https://github.com/rust-lang/cargo/issues/14434) is
+        // available in current toolchain's cargo, use it to build compile time deps only.
+        const COMP_TIME_DEPS_MIN_TOOLCHAIN_VERSION: semver::Version = semver::Version {
+            major: 1,
+            minor: 90,
+            patch: 0,
+            pre: semver::Prerelease::EMPTY,
+            build: semver::BuildMetadata::EMPTY,
+        };
+
+        let query_config = QueryConfig::Cargo(sysroot, manifest_path);
+        let toolchain = version::get(query_config, &config.extra_env).ok().flatten();
+        let cargo_comp_time_deps_available =
+            toolchain.is_some_and(|v| v >= COMP_TIME_DEPS_MIN_TOOLCHAIN_VERSION);
+
+        if cargo_comp_time_deps_available {
+            cmd.env("__CARGO_TEST_CHANNEL_OVERRIDE_DO_NOT_USE_THIS", "nightly");
+            cmd.arg("-Zunstable-options");
+            cmd.arg("--compile-time-deps");
+        } else if config.wrap_rustc_in_build_scripts {
             // Setup RUSTC_WRAPPER to point to `rust-analyzer` binary itself. We use
             // that to compile only proc macros and build scripts during the initial
             // `cargo check`.
+            // We don't need this if we are using `--compile-time-deps` flag.
             let myself = std::env::current_exe()?;
             cmd.env("RUSTC_WRAPPER", myself);
             cmd.env("RA_RUSTC_WRAPPER", "1");