Install rust-src when it is not found

crates/ra_project_model/src/sysroot.rs

@@ -47,8 +47,10 @@ impl Sysroot {
     }
 
     pub fn discover(cargo_toml: &Path) -> Result<Sysroot> {
-        let src = try_find_src_path(cargo_toml)?;
+        let mut src = try_find_src_path(cargo_toml)?;
 
+        if !src.exists() {
+            src = try_install_rust_src(cargo_toml)?;
             if !src.exists() {
                 Err(anyhow!(
                     "can't load standard library from sysroot\n\
@@ -58,6 +60,7 @@ impl Sysroot {
                     src.display(),
                 ))?;
             }
+        }
 
         let mut sysroot = Sysroot { crates: Arena::default() };
         for name in SYSROOT_CRATES.trim().lines() {
@@ -113,6 +116,26 @@ fn try_find_src_path(cargo_toml: &Path) -> Result<PathBuf> {
     Ok(sysroot_path.join("lib/rustlib/src/rust/src"))
 }
 
+fn try_install_rust_src(cargo_toml: &Path) -> Result<PathBuf> {
+    let rustup_output = Command::new("rustup")
+        .current_dir(cargo_toml.parent().unwrap())
+        .args(&["component", "add", "rust-src"])
+        .output()
+        .context("rustup component add rust-src failed")?;
+    if !rustup_output.status.success() {
+        match rustup_output.status.code() {
+            Some(code) => bail!(
+                "failed to install rust-src: rustup component add rust-src exited with code {}",
+                code
+            ),
+            None => bail!(
+                "failed to install rust-src: rustup component add rust-src terminated by signal"
+            ),
+        };
+    }
+    try_find_src_path(cargo_toml)
+}
+
 impl SysrootCrate {
     pub fn name(self, sysroot: &Sysroot) -> &str {
         &sysroot.crates[self].name

docs/user/readme.adoc

@@ -20,7 +20,9 @@ In theory, one should be able to just install the server binary and have it auto
 We are not there yet, so some editor specific setup is required.
 
 Additionally, rust-analyzer needs sources of the standard library.
-This commands adds them:
+When fails to locate them, rust-analyzer attempts to install them automatically.
+
+To add the sources manually, run the following command:
 
 ```bash
 $ rustup component add rust-src