1 files changed, 60 insertions, 0 deletions
diff --git a/src/tools/rust-analyzer/crates/project-model/src/rustc_cfg.rs b/src/tools/rust-analyzer/crates/project-model/src/rustc_cfg.rs
new file mode 100644
index 000000000..17e244d06
--- /dev/null
+++ b/src/tools/rust-analyzer/crates/project-model/src/rustc_cfg.rs
@@ -0,0 +1,60 @@
+//! Runs `rustc --print cfg` to get built-in cfg flags.
+
+use std::process::Command;
+
+use anyhow::Result;
+
+use crate::{cfg_flag::CfgFlag, utf8_stdout, ManifestPath};
+
+pub(crate) fn get(cargo_toml: Option<&ManifestPath>, target: Option<&str>) -> Vec<CfgFlag> {
+    let _p = profile::span("rustc_cfg::get");
+    let mut res = Vec::with_capacity(6 * 2 + 1);
+
+    // Some nightly-only cfgs, which are required for stdlib
+    res.push(CfgFlag::Atom("target_thread_local".into()));
+    for ty in ["8", "16", "32", "64", "cas", "ptr"] {
+        for key in ["target_has_atomic", "target_has_atomic_load_store"] {
+            res.push(CfgFlag::KeyValue { key: key.to_string(), value: ty.into() });
+        }
+    }
+
+    match get_rust_cfgs(cargo_toml, target) {
+        Ok(rustc_cfgs) => {
+            tracing::debug!(
+                "rustc cfgs found: {:?}",
+                rustc_cfgs
+                    .lines()
+                    .map(|it| it.parse::<CfgFlag>().map(|it| it.to_string()))
+                    .collect::<Vec<_>>()
+            );
+            res.extend(rustc_cfgs.lines().filter_map(|it| it.parse().ok()));
+        }
+        Err(e) => tracing::error!("failed to get rustc cfgs: {e:?}"),
+    }
+
+    res
+}
+
+fn get_rust_cfgs(cargo_toml: Option<&ManifestPath>, target: Option<&str>) -> Result<String> {
+    if let Some(cargo_toml) = cargo_toml {
+        let mut cargo_config = Command::new(toolchain::cargo());
+        cargo_config
+            .current_dir(cargo_toml.parent())
+            .args(&["-Z", "unstable-options", "rustc", "--print", "cfg"])
+            .env("RUSTC_BOOTSTRAP", "1");
+        if let Some(target) = target {
+            cargo_config.args(&["--target", target]);
+        }
+        match utf8_stdout(cargo_config) {
+            Ok(it) => return Ok(it),
+            Err(e) => tracing::debug!("{e:?}: falling back to querying rustc for cfgs"),
+        }
+    }
+    // using unstable cargo features failed, fall back to using plain rustc
+    let mut cmd = Command::new(toolchain::rustc());
+    cmd.args(&["--print", "cfg", "-O"]);
+    if let Some(target) = target {
+        cmd.args(&["--target", target]);
+    }
+    utf8_stdout(cmd)
+}