Auto merge of #13290 - poliorcetics:multiple-targets, r=Veykril

Support multiple targets for checkOnSave (in conjunction with cargo 1.64.0+)

This PR adds support for the ability to pass multiple `--target` flags when using
`cargo` 1.64.0+.

## Questions

I needed to change the type of two configurations options, but I did not plurialize the names to
avoid too much churn, should I ?

## Zulip thread

https://rust-lang.zulipchat.com/#narrow/stream/185405-t-compiler.2Frust-analyzer/topic/Issue.2013282.20.28supporting.20multiple.20targets.20with.201.2E64.2B.29

## Example

To see it working, on a macOS machine:

```sh
$ cd /tmp
$ cargo new cargo-multiple-targets-support-ra-test
$ cd !$
$ mkdir .cargo
$ echo '
[build]
target = [
    "aarch64-apple-darwin",
    "x86_64-apple-darwin",
]
' > .cargo/config.toml
$ echo '
fn main() {
    #[cfg(all(target_arch = "aarch64", target_os = "macos"))]
    {
        let a = std::fs::read_to_string("/tmp/test-read");
    }

    #[cfg(all(target_arch = "x86_64", target_os = "macos"))]
    {
        let a = std::fs::read_to_string("/tmp/test-read");
    }

    #[cfg(all(target_arch = "x86_64", target_os = "windows"))]
    {
        let a = std::fs::read_to_string("/tmp/test-read");
    }
}
' > src/main.rs
# launch your favorite editor with the version of RA from this PR
#
# You should see warnings under the first two `let a = ...` but not the third
```

## Screen

![Two panes of a terminal emulator, on the left pane is the main.rs file described above, with warnings for the first two let a = declaration, on the right pane is a display of the .cargo/config.toml, an ls of the current files in the directory and a call to cargo build to show the same warnings as in the editor on the left pane](https://user-images.githubusercontent.com/7951708/192122707-7a00606a-e581-4534-b9d5-b81c92694e8e.png)

Helps with #13282

crates/project-model/src/build_scripts.rs

@@ -69,7 +69,7 @@ impl WorkspaceBuildScripts {
                 cmd.args(&["check", "--quiet", "--workspace", "--message-format=json"]);
 
                 // --all-targets includes tests, benches and examples in addition to the
-                // default lib and bins. This is an independent concept from the --targets
+                // default lib and bins. This is an independent concept from the --target
                 // flag below.
                 cmd.arg("--all-targets");
 

crates/project-model/src/cargo_workspace.rs

@@ -270,11 +270,7 @@ impl CargoWorkspace {
         config: &CargoConfig,
         progress: &dyn Fn(String),
     ) -> Result<cargo_metadata::Metadata> {
-        let target = config
-            .target
-            .clone()
-            .or_else(|| cargo_config_build_target(cargo_toml, &config.extra_env))
-            .or_else(|| rustc_discover_host_triple(cargo_toml, &config.extra_env));
+        let targets = find_list_of_build_targets(config, cargo_toml);
 
         let mut meta = MetadataCommand::new();
         meta.cargo_path(toolchain::cargo());
@@ -294,8 +290,12 @@ impl CargoWorkspace {
         }
         meta.current_dir(current_dir.as_os_str());
 
-        if let Some(target) = target {
-            meta.other_options(vec![String::from("--filter-platform"), target]);
+        if !targets.is_empty() {
+            let other_options: Vec<_> = targets
+                .into_iter()
+                .flat_map(|target| ["--filter-platform".to_string(), target])
+                .collect();
+            meta.other_options(other_options);
         }
 
         // FIXME: Fetching metadata is a slow process, as it might require
@@ -469,6 +469,19 @@ impl CargoWorkspace {
     }
 }
 
+fn find_list_of_build_targets(config: &CargoConfig, cargo_toml: &ManifestPath) -> Vec<String> {
+    if let Some(target) = &config.target {
+        return [target.into()].to_vec();
+    }
+
+    let build_targets = cargo_config_build_target(cargo_toml, &config.extra_env);
+    if !build_targets.is_empty() {
+        return build_targets;
+    }
+
+    rustc_discover_host_triple(cargo_toml, &config.extra_env).into_iter().collect()
+}
+
 fn rustc_discover_host_triple(
     cargo_toml: &ManifestPath,
     extra_env: &FxHashMap<String, String>,
@@ -499,7 +512,7 @@ fn rustc_discover_host_triple(
 fn cargo_config_build_target(
     cargo_toml: &ManifestPath,
     extra_env: &FxHashMap<String, String>,
-) -> Option<String> {
+) -> Vec<String> {
     let mut cargo_config = Command::new(toolchain::cargo());
     cargo_config.envs(extra_env);
     cargo_config
@@ -507,12 +520,21 @@ fn cargo_config_build_target(
         .args(&["-Z", "unstable-options", "config", "get", "build.target"])
         .env("RUSTC_BOOTSTRAP", "1");
     // if successful we receive `build.target = "target-triple"`
+    // or `build.target = ["<target 1>", ..]`
     tracing::debug!("Discovering cargo config target by {:?}", cargo_config);
-    match utf8_stdout(cargo_config) {
-        Ok(stdout) => stdout
-            .strip_prefix("build.target = \"")
-            .and_then(|stdout| stdout.strip_suffix('"'))
-            .map(ToOwned::to_owned),
-        Err(_) => None,
-    }
+    utf8_stdout(cargo_config).map(parse_output_cargo_config_build_target).unwrap_or_default()
+}
+
+fn parse_output_cargo_config_build_target(stdout: String) -> Vec<String> {
+    let trimmed = stdout.trim_start_matches("build.target = ").trim_matches('"');
+
+    if !trimmed.starts_with('[') {
+        return [trimmed.to_string()].to_vec();
+    }
+
+    let res = serde_json::from_str(trimmed);
+    if let Err(e) = &res {
+        tracing::warn!("Failed to parse `build.target` as an array of target: {}`", e);
+    }
+    res.unwrap_or_default()
 }