cargo doc --open always respect request_kind

src/cargo/core/compiler/compilation.rs

@@ -56,7 +56,7 @@ pub struct Compilation<'cfg> {
     pub cdylibs: Vec<UnitOutput>,
 
     /// The crate names of the root units specified on the command-line.
-    pub root_crate_names: Vec<String>,
+    pub root_crate_names: Vec<(String, CompileKind)>,
 
     /// All directories for the output of native build commands.
     ///

src/cargo/core/compiler/context/mod.rs

@@ -321,9 +321,12 @@ impl<'a, 'cfg> Context<'a, 'cfg> {
         }
         self.primary_packages
             .extend(self.bcx.roots.iter().map(|u| u.pkg.package_id()));
-        self.compilation
-            .root_crate_names
-            .extend(self.bcx.roots.iter().map(|u| u.target.crate_name()));
+        self.compilation.root_crate_names.extend(
+            self.bcx
+                .roots
+                .iter()
+                .map(|u| (u.target.crate_name(), u.kind.clone())),
+        );
 
         self.record_units_requiring_metadata();
 

src/cargo/ops/cargo_doc.rs

@@ -20,11 +20,21 @@ pub fn doc(ws: &Workspace<'_>, options: &DocOptions) -> CargoResult<()> {
     let compilation = ops::compile(ws, &options.compile_opts)?;
 
     if options.open_result {
-        let name = &compilation
+        // The open behavior is as follows:
+        // cargo doc --open:
+        //  - Pick the first root unit that was built for host.
+        //  - If none found, pick the first one(whatever it's target is).
+        // cargo doc --target TARGET --open:
+        //  - Pick the first root unit for the given target.
+        //  - If none found, pick the first one(whatever it's target is).
+        let request_kind = options.compile_opts.build_config.single_requested_kind()?;
+        let (name, kind) = &compilation
             .root_crate_names
-            .get(0)
+            .iter()
+            .find(|(_, kind)| *kind == request_kind)
+            .or_else(|| compilation.root_crate_names.get(0))
             .ok_or_else(|| anyhow::anyhow!("no crates with documentation"))?;
-        let kind = options.compile_opts.build_config.single_requested_kind()?;
+
         let path = compilation.root_output[&kind]
             .with_file_name("doc")
             .join(&name)