Use 'cargo check' to build the sysroot and target crate

Fixes rust-lang#1057

I'm using my original approach from PR rust-lang#1048. Ideally, we would
distinguish between build-deps/dependencies/'final crate' via a
different approach (e.g. the target directory). However, I
haven't been able to get that to work just yet.

However, everything should be working with the approach I'm using. At a
minimum, we can use this PR to verify that everything works as expected
when we don't actually produce native build outputs.

Cargo.toml

@@ -50,6 +50,7 @@ rustc-workspace-hack = "1.0.0"
 # between "cargo build" and "cargo intall".
 num-traits = "*"
 serde = { version = "*", features = ["derive"] }
+serde_json = "1.0.44"
 
 [build-dependencies]
 vergen = "3"

src/bin/cargo-miri.rs

@@ -6,7 +6,7 @@ use std::ops::Not;
 use std::path::{Path, PathBuf};
 use std::process::Command;
 
-const XARGO_MIN_VERSION: (u32, u32, u32) = (0, 3, 17);
+const XARGO_MIN_VERSION: (u32, u32, u32) = (0, 3, 19);
 
 const CARGO_MIRI_HELP: &str = r#"Interprets bin crates and tests in Miri
 
@@ -84,7 +84,37 @@ fn get_arg_flag_value(name: &str) -> Option<String> {
     }
 }
 
-fn list_targets() -> impl Iterator<Item = cargo_metadata::Target> {
+fn is_build_dep(mut args: impl Iterator<Item = String>) -> bool {
+    args.any(|arg| arg.starts_with("--emit=") && arg.contains("link"))
+}
+
+// Returns whether or not Cargo invoked the wrapper (this binary) to compile
+// the final, target crate (either a test for 'cargo test', or a binary for 'cargo run')
+// Right now, this is an awful hack that checks several different pieces of information
+// to try to figure out if the crate being compiled is the right one.
+// Ideally, Cargo would set en environment variable indicating whether or
+// not the wrapper is being invoked on the target crate.
+// For now, this is the best we can do
+fn is_target_crate(is_build_script: bool) -> bool {
+    // Cargo sets this to the directory containing the manifest of the crate
+    // the wrapper is being invoekd to compile. This should be unique
+    // across the entire build (except for build scripts, which we handle below).
+    // We cannot check the crate name, since this may not be unique
+    // (e.g. if the build contains multiple versions of the same crate,
+    // or the same crate from multiple sources)
+    let manifest_dir = std::env::var("CARGO_MANIFEST_DIR").ok();
+
+    // The manifest directory for our target crate. This is set by `cargo-miri`
+    // (the original invoation by the user) by using `cargo_metadata` to locate
+    // the manifest.
+    let expected_dir = std::env::var("MIRI_MAGIC_DIR").expect("MIRI_MAGIC_DIR not set!");
+
+    manifest_dir == Some(expected_dir) && !is_build_script
+
+}
+
+
+fn read_cargo_metadata() -> (impl Iterator<Item = cargo_metadata::Target>, String) {
     // We need to get the manifest, and then the metadata, to enumerate targets.
     let manifest_path =
         get_arg_flag_value("--manifest-path").map(|m| Path::new(&m).canonicalize().unwrap());
@@ -124,7 +154,7 @@ fn list_targets() -> impl Iterator<Item = cargo_metadata::Target> {
     let package = metadata.packages.remove(package_index);
 
     // Finally we got the list of targets to build
-    package.targets.into_iter()
+    (package.targets.into_iter(), metadata.workspace_root.to_string_lossy().to_string())
 }
 
 /// Returns the path to the `miri` binary
@@ -197,7 +227,7 @@ fn xargo() -> Command {
         // Bootstrap tells us where to find xargo
         Command::new(val)
     } else {
-        Command::new("xargo")
+        Command::new("xargo-check")
     }
 }
 
@@ -458,8 +488,10 @@ fn in_cargo_miri() {
         return;
     }
 
+    let (targets, root_dir) = read_cargo_metadata();
+
     // Now run the command.
-    for target in list_targets() {
+    for target in targets {
         let mut args = std::env::args().skip(skip);
         let kind = target
             .kind
@@ -469,7 +501,8 @@ fn in_cargo_miri() {
         // change to add additional arguments. `FLAGS` is set to identify
         // this target.  The user gets to control what gets actually passed to Miri.
         let mut cmd = cargo();
-        cmd.arg("rustc");
+        cmd.arg("check");
+        cmd.arg("--target").arg("x86_64-unknown-linux-gnu");
         match (subcommand, kind.as_str()) {
             (MiriCommand::Run, "bin") => {
                 // FIXME: we just run all the binaries here.
@@ -496,10 +529,15 @@ fn in_cargo_miri() {
             }
             cmd.arg(arg);
         }
+
+        let args_vec: Vec<String> = args.collect();
+        cmd.env("MIRI_MAGIC_DIR", root_dir.clone());
+        cmd.env("MIRI_MAGIC_ARGS", serde_json::to_string(&args_vec).expect("failed to serialize args"));
+
         // Add `--` (to end the `cargo` flags), and then the user flags. We add markers around the
         // user flags to be able to identify them later.  "cargo rustc" adds more stuff after this,
         // so we have to mark both the beginning and the end.
-        cmd.arg("--").arg("cargo-miri-marker-begin").args(args).arg("cargo-miri-marker-end");
+        //cmd.arg("--").arg("cargo-miri-marker-begin").args(args).arg("cargo-miri-marker-end");
         let path = std::env::current_exe().expect("current executable path invalid");
         cmd.env("RUSTC_WRAPPER", path);
         if verbose {
@@ -519,25 +557,27 @@ fn inside_cargo_rustc() {
     let sysroot = std::env::var("MIRI_SYSROOT").expect("The wrapper should have set MIRI_SYSROOT");
 
     let rustc_args = std::env::args().skip(2); // skip `cargo rustc`
-    let mut args: Vec<String> =
-        rustc_args.chain(Some("--sysroot".to_owned())).chain(Some(sysroot)).collect();
-    args.splice(0..0, miri::miri_default_args().iter().map(ToString::to_string));
+
+    let in_build_script = is_build_dep(std::env::args().skip(2));
+
+    let mut args = if in_build_script {
+        rustc_args.collect()
+    } else {
+        let mut args: Vec<String> = rustc_args
+            .chain(Some("--sysroot".to_owned()))
+            .chain(Some(sysroot))
+            .collect();
+        args.splice(0..0, miri::miri_default_args().iter().map(ToString::to_string));
+        args
+    };
 
     // See if we can find the `cargo-miri` markers. Those only get added to the binary we want to
     // run. They also serve to mark the user-defined arguments, which we have to move all the way
     // to the end (they get added somewhere in the middle).
     let needs_miri =
-        if let Some(begin) = args.iter().position(|arg| arg == "cargo-miri-marker-begin") {
-            let end = args
-                .iter()
-                .position(|arg| arg == "cargo-miri-marker-end")
-                .expect("cannot find end marker");
-            // These mark the user arguments. We remove the first and last as they are the markers.
-            let mut user_args = args.drain(begin..=end);
-            assert_eq!(user_args.next().unwrap(), "cargo-miri-marker-begin");
-            assert_eq!(user_args.next_back().unwrap(), "cargo-miri-marker-end");
-            // Collect the rest and add it back at the end.
-            let mut user_args = user_args.collect::<Vec<String>>();
+        if is_target_crate(in_build_script) {
+            let magic = std::env::var("MIRI_MAGIC_ARGS").expect("missing MIRI_MAGIC_ARGS");
+            let mut user_args: Vec<String> = serde_json::from_str(&magic).expect("failed to deserialize args");
             args.append(&mut user_args);
             // Run this in Miri.
             true