Add crate type flag to rustc command

src/bin/cargo/commands/rustc.rs

@@ -3,6 +3,7 @@ use cargo::ops;
 use cargo::util::interning::InternedString;
 
 const PRINT_ARG_NAME: &str = "print";
+const CRATE_TYPE_ARG_NAME: &str = "crate-type";
 
 pub fn cli() -> App {
     subcommand("rustc")
@@ -35,6 +36,11 @@ pub fn cli() -> App {
             )
             .value_name("INFO"),
         )
+        .arg(multi_opt(
+            CRATE_TYPE_ARG_NAME,
+            "CRATE-TYPE",
+            "Comma separated list of types of crates for the compiler to emit (unstable)",
+        ))
         .arg_target_dir()
         .arg_manifest_path()
         .arg_message_format()
@@ -75,8 +81,18 @@ pub fn exec(config: &mut Config, args: &ArgMatches<'_>) -> CliResult {
             .cli_unstable()
             .fail_if_stable_opt(PRINT_ARG_NAME, 9357)?;
         ops::print(&ws, &compile_opts, opt_value)?;
-    } else {
-        ops::compile(&ws, &compile_opts)?;
+        return Ok(());
     }
+    let crate_types = values(args, CRATE_TYPE_ARG_NAME);
+    compile_opts.target_rustc_crate_types = if crate_types.is_empty() {
+        None
+    } else {
+        config
+            .cli_unstable()
+            .fail_if_stable_opt(CRATE_TYPE_ARG_NAME, 10083)?;
+        Some(crate_types)
+    };
+    ops::compile(&ws, &compile_opts)?;
+
     Ok(())
 }

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

@@ -33,6 +33,9 @@ pub struct BuildContext<'a, 'cfg> {
     /// Extra compiler args for either `rustc` or `rustdoc`.
     pub extra_compiler_args: HashMap<Unit, Vec<String>>,
 
+    // Crate types for `rustc`.
+    pub target_rustc_crate_types: HashMap<Unit, Vec<String>>,
+
     /// Package downloader.
     ///
     /// This holds ownership of the `Package` objects.
@@ -61,6 +64,7 @@ impl<'a, 'cfg> BuildContext<'a, 'cfg> {
         build_config: &'a BuildConfig,
         profiles: Profiles,
         extra_compiler_args: HashMap<Unit, Vec<String>>,
+        target_rustc_crate_types: HashMap<Unit, Vec<String>>,
         target_data: RustcTargetData<'cfg>,
         roots: Vec<Unit>,
         unit_graph: UnitGraph,
@@ -80,6 +84,7 @@ impl<'a, 'cfg> BuildContext<'a, 'cfg> {
             build_config,
             profiles,
             extra_compiler_args,
+            target_rustc_crate_types,
             target_data,
             roots,
             unit_graph,
@@ -127,4 +132,8 @@ impl<'a, 'cfg> BuildContext<'a, 'cfg> {
     pub fn extra_args_for(&self, unit: &Unit) -> Option<&Vec<String>> {
         self.extra_compiler_args.get(unit)
     }
+
+    pub fn rustc_crate_types_args_for(&self, unit: &Unit) -> Option<&Vec<String>> {
+        self.target_rustc_crate_types.get(unit)
+    }
 }

src/cargo/core/compiler/mod.rs

@@ -861,9 +861,20 @@ fn build_base_args(
     add_error_format_and_color(cx, cmd, cx.rmeta_required(unit));
     add_allow_features(cx, cmd);
 
+    let mut contains_dy_lib = false;
     if !test {
+        let mut crate_types = &crate_types
+            .iter()
+            .map(|t| t.as_str().to_string())
+            .collect::<Vec<String>>();
+        if let Some(types) = cx.bcx.rustc_crate_types_args_for(unit) {
+            crate_types = types;
+        }
         for crate_type in crate_types.iter() {
-            cmd.arg("--crate-type").arg(crate_type.as_str());
+            cmd.arg("--crate-type").arg(crate_type);
+            if crate_type == CrateType::Dylib.as_str() {
+                contains_dy_lib = true;
+            }
         }
     }
 
@@ -879,7 +890,7 @@ fn build_base_args(
     }
 
     let prefer_dynamic = (unit.target.for_host() && !unit.target.is_custom_build())
-        || (crate_types.contains(&CrateType::Dylib) && !cx.is_primary_package(unit));
+        || (contains_dy_lib && !cx.is_primary_package(unit));
     if prefer_dynamic {
         cmd.arg("-C").arg("prefer-dynamic");
     }

src/cargo/ops/cargo_compile.rs

@@ -71,6 +71,8 @@ pub struct CompileOptions {
     /// The specified target will be compiled with all the available arguments,
     /// note that this only accounts for the *final* invocation of rustc
     pub target_rustc_args: Option<Vec<String>>,
+    /// Crate types to be passed to rustc (single target only)
+    pub target_rustc_crate_types: Option<Vec<String>>,
     /// Extra arguments passed to all selected targets for rustdoc.
     pub local_rustdoc_args: Option<Vec<String>>,
     /// Whether the `--document-private-items` flags was specified and should
@@ -92,6 +94,7 @@ impl<'a> CompileOptions {
             },
             target_rustdoc_args: None,
             target_rustc_args: None,
+            target_rustc_crate_types: None,
             local_rustdoc_args: None,
             rustdoc_document_private_items: false,
             honor_rust_version: true,
@@ -332,6 +335,7 @@ pub fn create_bcx<'a, 'cfg>(
         ref filter,
         ref target_rustdoc_args,
         ref target_rustc_args,
+        ref target_rustc_crate_types,
         ref local_rustdoc_args,
         rustdoc_document_private_items,
         honor_rust_version,
@@ -644,6 +648,28 @@ pub fn create_bcx<'a, 'cfg>(
         }
     }
 
+    let mut crate_types = HashMap::new();
+    if let Some(args) = target_rustc_crate_types {
+        if units.len() != 1 {
+            anyhow::bail!(
+                "crate types to rustc can only be passed to one \
+                 target, consider filtering\nthe package by passing, \
+                 e.g., `--lib` or `--example` to specify a single target"
+            );
+        }
+        match units[0].target.kind() {
+            TargetKind::Lib(_) | TargetKind::ExampleLib(_) => {
+                crate_types.insert(units[0].clone(), args.clone());
+            }
+            _ => {
+                anyhow::bail!(
+                    "crate types can only be specified for libraries and example libraries.\n\
+                    Binaries, tests, and benchmarks are always the `bin` crate type"
+                );
+            }
+        }
+    }
+
     if honor_rust_version {
         // Remove any pre-release identifiers for easier comparison
         let current_version = &target_data.rustc.version;
@@ -680,6 +706,7 @@ pub fn create_bcx<'a, 'cfg>(
         build_config,
         profiles,
         extra_compiler_args,
+        crate_types,
         target_data,
         units,
         unit_graph,

src/cargo/ops/cargo_package.rs

@@ -763,6 +763,7 @@ fn run_verify(
             },
             target_rustdoc_args: None,
             target_rustc_args: rustc_args,
+            target_rustc_crate_types: None,
             local_rustdoc_args: None,
             rustdoc_document_private_items: false,
             honor_rust_version: true,

src/cargo/util/command_prelude.rs

@@ -542,6 +542,7 @@ pub trait ArgMatchesExt {
             ),
             target_rustdoc_args: None,
             target_rustc_args: None,
+            target_rustc_crate_types: None,
             local_rustdoc_args: None,
             rustdoc_document_private_items: false,
             honor_rust_version: !self._is_present("ignore-rust-version"),

src/doc/src/reference/unstable.md

@@ -83,6 +83,7 @@ Each new feature described below should explain how to use it.
     * [build-std-features](#build-std-features) — Sets features to use with the standard library.
     * [binary-dep-depinfo](#binary-dep-depinfo) — Causes the dep-info file to track binary dependencies.
     * [panic-abort-tests](#panic-abort-tests) — Allows running tests with the "abort" panic strategy.
+    * [crate-type](#crate-type) - Supports passing crate types to the compiler.
 * rustdoc
     * [`doctest-in-workspace`](#doctest-in-workspace) — Fixes workspace-relative paths when running doctests.
     * [rustdoc-map](#rustdoc-map) — Provides mappings for documentation to link to external sites like [docs.rs](https://docs.rs/).
@@ -555,6 +556,23 @@ like to stabilize it somehow!
 
 [rust-lang/rust#64158]: https://github.com/rust-lang/rust/pull/64158
 
+### crate-type
+* Tracking Issue: [#10083](https://github.com/rust-lang/cargo/issues/10083)
+* RFC: [#3180](https://github.com/rust-lang/rfcs/pull/3180)
+* Original Pull Request: [#10093](https://github.com/rust-lang/cargo/pull/10093)
+
+`cargo rustc --crate-type=lib,cdylib` forwards the `--crate-type` flag to `rustc`.
+This runs `rustc` with the corresponding
+[`--crate-type`](https://doc.rust-lang.org/rustc/command-line-arguments.html#--crate-type-a-list-of-types-of-crates-for-the-compiler-to-emit)
+flag, and compiling.
+
+When using it, it requires the `-Z unstable-options`
+command-line option:
+
+```console
+cargo rustc --crate-type lib,cdylib -Z unstable-options
+```
+
 ### config-cli
 * Tracking Issue: [#7722](https://github.com/rust-lang/cargo/issues/7722)