Automatically detect the rustc-src directory (fixes #3517).

If the configured rustcSource was not set, then try to automatically
detect a source for the sysroot rustc directory.

Author: bnjbvr

crates/project_model/src/sysroot.rs

@@ -15,6 +15,7 @@ use crate::utf8_stdout;
 #[derive(Default, Debug, Clone, Eq, PartialEq)]
 pub struct Sysroot {
     crates: Arena<SysrootCrateData>,
+    pub rustc_src_dir: Option<AbsPathBuf>,
 }
 
 pub(crate) type SysrootCrate = Idx<SysrootCrateData>;
@@ -51,13 +52,15 @@ impl Sysroot {
     pub fn discover(cargo_toml: &AbsPath) -> Result<Sysroot> {
         log::debug!("Discovering sysroot for {}", cargo_toml.display());
         let current_dir = cargo_toml.parent().unwrap();
-        let sysroot_src_dir = discover_sysroot_src_dir(current_dir)?;
-        let res = Sysroot::load(&sysroot_src_dir)?;
+        let sysroot_dir = discover_sysroot_dir(current_dir)?;
+        let sysroot_src_dir = discover_sysroot_src_dir(&sysroot_dir, current_dir)?;
+        let rustc_src_dir = get_rustc_src(&sysroot_dir);
+        let res = Sysroot::load(&sysroot_src_dir, rustc_src_dir)?;
         Ok(res)
     }
 
-    pub fn load(sysroot_src_dir: &AbsPath) -> Result<Sysroot> {
-        let mut sysroot = Sysroot { crates: Arena::default() };
+    pub fn load(sysroot_src_dir: &AbsPath, rustc_src_dir: Option<AbsPathBuf>) -> Result<Sysroot> {
+        let mut sysroot = Sysroot { crates: Arena::default(), rustc_src_dir };
 
         for name in SYSROOT_CRATES.trim().lines() {
             let root = [format!("{}/src/lib.rs", name), format!("lib{}/lib.rs", name)]
@@ -110,7 +113,18 @@ impl Sysroot {
     }
 }
 
-fn discover_sysroot_src_dir(current_dir: &AbsPath) -> Result<AbsPathBuf> {
+fn discover_sysroot_dir(current_dir: &AbsPath) -> Result<AbsPathBuf> {
+    let mut rustc = Command::new(toolchain::rustc());
+    rustc.current_dir(current_dir).args(&["--print", "sysroot"]);
+    log::debug!("Discovering sysroot by {:?}", rustc);
+    let stdout = utf8_stdout(rustc)?;
+    Ok(AbsPathBuf::assert(PathBuf::from(stdout)))
+}
+
+fn discover_sysroot_src_dir(
+    sysroot_path: &AbsPathBuf,
+    current_dir: &AbsPath,
+) -> Result<AbsPathBuf> {
     if let Ok(path) = env::var("RUST_SRC_PATH") {
         let path = AbsPathBuf::try_from(path.as_str())
             .map_err(|path| format_err!("RUST_SRC_PATH must be absolute: {}", path.display()))?;
@@ -122,14 +136,6 @@ fn discover_sysroot_src_dir(current_dir: &AbsPath) -> Result<AbsPathBuf> {
         log::debug!("RUST_SRC_PATH is set, but is invalid (no core: {:?}), ignoring", core);
     }
 
-    let sysroot_path = {
-        let mut rustc = Command::new(toolchain::rustc());
-        rustc.current_dir(current_dir).args(&["--print", "sysroot"]);
-        log::debug!("Discovering sysroot by {:?}", rustc);
-        let stdout = utf8_stdout(rustc)?;
-        AbsPathBuf::assert(PathBuf::from(stdout))
-    };
-
     get_rust_src(&sysroot_path)
         .or_else(|| {
             let mut rustup = Command::new(toolchain::rustup());
@@ -149,6 +155,16 @@ try installing the Rust source the same way you installed rustc",
         })
 }
 
+fn get_rustc_src(sysroot_path: &AbsPath) -> Option<AbsPathBuf> {
+    let rustc_src = sysroot_path.join("lib/rustlib/rustc-src/rust/compiler/rustc/Cargo.toml");
+    log::debug!("Checking for rustc source code: {}", rustc_src.display());
+    if rustc_src.exists() {
+        Some(rustc_src)
+    } else {
+        None
+    }
+}
+
 fn get_rust_src(sysroot_path: &AbsPath) -> Option<AbsPathBuf> {
     // Try the new path first since the old one still exists.
     let rust_src = sysroot_path.join("lib/rustlib/src/rust");

crates/project_model/src/workspace.rs

@@ -108,6 +108,7 @@ impl ProjectWorkspace {
                             cargo_version
                         )
                     })?;
+
                 let sysroot = if config.no_sysroot {
                     Sysroot::default()
                 } else {
@@ -119,7 +120,15 @@ impl ProjectWorkspace {
                     })?
                 };
 
-                let rustc = if let Some(rustc_dir) = &config.rustc_source {
+                let rustc_dir = if let Some(rustc_dir) = &config.rustc_source {
+                    Some(rustc_dir)
+                } else if let Some(rustc_dir) = &sysroot.rustc_src_dir {
+                    Some(rustc_dir)
+                } else {
+                    None
+                };
+
+                let rustc = if let Some(rustc_dir) = rustc_dir {
                     Some(
                         CargoWorkspace::from_cargo_metadata(&rustc_dir, config, progress)
                             .with_context(|| {
@@ -142,7 +151,7 @@ impl ProjectWorkspace {
         target: Option<&str>,
     ) -> Result<ProjectWorkspace> {
         let sysroot = match &project_json.sysroot_src {
-            Some(path) => Some(Sysroot::load(path)?),
+            Some(path) => Some(Sysroot::load(path, None)?),
             None => None,
         };
         let rustc_cfg = rustc_cfg::get(target);