Auto merge of #3546 - matthiaskrgr:fix_install, r=oli-obk

Revert "Merge pull request #3257 from o01eg/remove-sysroot"

This reverts commit 041c49c1ed11b016d6ab9379643bb1da2adf5bfe, reversing
changes made to 1df5766cbb559aab0ad5c2296d8b768182b5186c.

The PR broke running a cargo-install'd clippy.
The installed clippy would not be able to find a crate for std.

Fixes #3523
Reopens #2874

1 files changed, 38 insertions, 6 deletions

diff --git a/src/driver.rs b/src/driver.rs
index 0df2d898860..269228988f7 100644
--- a/src/driver.rs
+++ b/src/driver.rs
@@ -23,7 +23,7 @@ use self::rustc_driver::{driver::CompileController, Compilation};
 
 use std::convert::TryInto;
 use std::path::Path;
-use std::process::exit;
+use std::process::{exit, Command};
 
 fn show_version() {
     println!(env!("CARGO_PKG_VERSION"));
@@ -40,22 +40,54 @@ pub fn main() {
                 exit(0);
             }
 
+            let sys_root = option_env!("SYSROOT")
+                .map(String::from)
+                .or_else(|| std::env::var("SYSROOT").ok())
+                .or_else(|| {
+                    let home = option_env!("RUSTUP_HOME").or(option_env!("MULTIRUST_HOME"));
+                    let toolchain = option_env!("RUSTUP_TOOLCHAIN").or(option_env!("MULTIRUST_TOOLCHAIN"));
+                    home.and_then(|home| toolchain.map(|toolchain| format!("{}/toolchains/{}", home, toolchain)))
+                })
+                .or_else(|| {
+                    Command::new("rustc")
+                        .arg("--print")
+                        .arg("sysroot")
+                        .output()
+                        .ok()
+                        .and_then(|out| String::from_utf8(out.stdout).ok())
+                        .map(|s| s.trim().to_owned())
+                })
+                .expect("need to specify SYSROOT env var during clippy compilation, or use rustup or multirust");
+
             // Setting RUSTC_WRAPPER causes Cargo to pass 'rustc' as the first argument.
             // We're invoking the compiler programmatically, so we ignore this/
-            let mut args: Vec<String> = env::args().collect();
-            if args.len() <= 1 {
+            let mut orig_args: Vec<String> = env::args().collect();
+            if orig_args.len() <= 1 {
                 std::process::exit(1);
             }
-            if Path::new(&args[1]).file_stem() == Some("rustc".as_ref()) {
+            if Path::new(&orig_args[1]).file_stem() == Some("rustc".as_ref()) {
                 // we still want to be able to invoke it normally though
-                args.remove(1);
+                orig_args.remove(1);
             }
+            // this conditional check for the --sysroot flag is there so users can call
+            // `clippy_driver` directly
+            // without having to pass --sysroot or anything
+            let mut args: Vec<String> = if orig_args.iter().any(|s| s == "--sysroot") {
+                orig_args.clone()
+            } else {
+                orig_args
+                    .clone()
+                    .into_iter()
+                    .chain(Some("--sysroot".to_owned()))
+                    .chain(Some(sys_root))
+                    .collect()
+            };
 
             // this check ensures that dependencies are built but not linted and the final
             // crate is
             // linted but not built
             let clippy_enabled = env::var("CLIPPY_TESTS").ok().map_or(false, |val| val == "true")
-                || args.iter().any(|s| s == "--emit=dep-info,metadata");
+                || orig_args.iter().any(|s| s == "--emit=dep-info,metadata");
 
             if clippy_enabled {
                 args.extend_from_slice(&["--cfg".to_owned(), r#"feature="cargo-clippy""#.to_owned()]);