From 8989fb8315538aece975663c3be4aba867e9ee86 Mon Sep 17 00:00:00 2001
From: Lukas Wirth <lukastw97@gmail.com>
Date: Sat, 8 May 2021 18:17:18 +0200
Subject: Discover rustc_cfg through unstable cargo options

---
 crates/project_model/src/cargo_workspace.rs | 71 +++++++++++++++++++----------
 1 file changed, 48 insertions(+), 23 deletions(-)

(limited to 'crates/project_model/src/cargo_workspace.rs')

diff --git a/crates/project_model/src/cargo_workspace.rs b/crates/project_model/src/cargo_workspace.rs
index bc6e20341..f1ad00d36 100644
--- a/crates/project_model/src/cargo_workspace.rs
+++ b/crates/project_model/src/cargo_workspace.rs
@@ -201,31 +201,12 @@ impl CargoWorkspace {
         if let Some(parent) = cargo_toml.parent() {
             meta.current_dir(parent.to_path_buf());
         }
-        let target = if let Some(target) = config.target.as_ref() {
+        let target = if let Some(target) = &config.target {
             Some(target.clone())
+        } else if let stdout @ Some(_) = cargo_config_build_target(cargo_toml) {
+            stdout
         } else {
-            // cargo metadata defaults to giving information for _all_ targets.
-            // In the absence of a preference from the user, we use the host platform.
-            let mut rustc = Command::new(toolchain::rustc());
-            rustc.current_dir(cargo_toml.parent().unwrap()).arg("-vV");
-            log::debug!("Discovering host platform by {:?}", rustc);
-            match utf8_stdout(rustc) {
-                Ok(stdout) => {
-                    let field = "host: ";
-                    let target = stdout.lines().find_map(|l| l.strip_prefix(field));
-                    if let Some(target) = target {
-                        Some(target.to_string())
-                    } else {
-                        // If we fail to resolve the host platform, it's not the end of the world.
-                        log::info!("rustc -vV did not report host platform, got:\n{}", stdout);
-                        None
-                    }
-                }
-                Err(e) => {
-                    log::warn!("Failed to discover host platform: {}", e);
-                    None
-                }
-            }
+            rustc_discover_host_triple(cargo_toml)
         };
         if let Some(target) = target {
             meta.other_options(vec![String::from("--filter-platform"), target]);
@@ -368,3 +349,47 @@ impl CargoWorkspace {
         self.packages.iter().filter(|(_, v)| v.name == name).count() == 1
     }
 }
+
+fn rustc_discover_host_triple(cargo_toml: &AbsPath) -> Option<String> {
+    let mut rustc = Command::new(toolchain::rustc());
+    rustc.current_dir(cargo_toml.parent().unwrap()).arg("-vV");
+    log::debug!("Discovering host platform by {:?}", rustc);
+    match utf8_stdout(rustc) {
+        Ok(stdout) => {
+            let field = "host: ";
+            let target = stdout.lines().find_map(|l| l.strip_prefix(field));
+            if let Some(target) = target {
+                Some(target.to_string())
+            } else {
+                // If we fail to resolve the host platform, it's not the end of the world.
+                log::info!("rustc -vV did not report host platform, got:\n{}", stdout);
+                None
+            }
+        }
+        Err(e) => {
+            log::warn!("Failed to discover host platform: {}", e);
+            None
+        }
+    }
+}
+
+fn cargo_config_build_target(cargo_toml: &AbsPath) -> Option<String> {
+    let mut cargo_config = Command::new(toolchain::cargo());
+    cargo_config.current_dir(cargo_toml.parent().unwrap()).args(&[
+        "+nightly",
+        "-Z",
+        "unstable-options",
+        "config",
+        "get",
+        "build.target",
+    ]);
+    // if successful we receive `build.target = "target-triple"`
+    log::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,
+    }
+}
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