Add support for rustc sysroot

Signed-off-by: xizheyin <xizheyin@smail.nju.edu.cn>

Author: xizheyin

compiler/rustc_errors/src/emitter.rs

@@ -13,7 +13,8 @@ use std::error::Report;
 use std::io::prelude::*;
 use std::io::{self, IsTerminal};
 use std::iter;
-use std::path::Path;
+use std::path::{Path, PathBuf};
+use std::process::Command;
 use std::sync::Arc;
 
 use derive_setters::Setters;
@@ -3571,9 +3572,22 @@ fn is_external_library(sm: &SourceMap, span: Span) -> bool {
 
         let registry_path = cargo_home.join("registry").join("src");
         let toolchain_path = rustup_home.join("toolchains");
+        let sysroot = get_rustc_sysroot();
 
-        path.starts_with(&registry_path) || path.starts_with(&toolchain_path)
+        path.starts_with(&registry_path)
+            || path.starts_with(&toolchain_path)
+            || sysroot.as_ref().map_or(false, |sr| path.starts_with(sr))
     } else {
         false
     }
 }
+
+fn get_rustc_sysroot() -> Option<PathBuf> {
+    let rustc_path = std::env::var("RUSTC").unwrap_or_else(|_| "rustc".to_string());
+    match Command::new(rustc_path).arg("--print").arg("sysroot").output() {
+        Ok(output) if output.status.success() => {
+            String::from_utf8(output.stdout).ok().map(|s| PathBuf::from(s.trim()))
+        }
+        _ => None,
+    }
+}