Add support for local Rustflags

For some scenarios it is better to not set Rustflags for all crates
in the dependency graph and instead only set it for the top-level
crate.
For example rust-lang/cargo#8716
can be avoided in some scenarios by setting the rustflags via
rustc, which allows for faster rebuilds in such cases.

Author: jschwe

cmake/Corrosion.cmake

@@ -253,6 +253,7 @@ function(_add_cargo_build)
     endif()
 
     set(global_rustflags_target_property "$<TARGET_GENEX_EVAL:${target_name},$<TARGET_PROPERTY:${target_name},INTERFACE_CORROSION_RUSTFLAGS>>")
+    set(local_rustflags_target_property  "$<TARGET_GENEX_EVAL:${target_name},$<TARGET_PROPERTY:${target_name},INTERFACE_CORROSION_LOCAL_RUSTFLAGS>>")
 
     set(features_target_property "$<GENEX_EVAL:$<TARGET_PROPERTY:${target_name},${_CORR_PROP_FEATURES}>>")
     set(features_genex "$<$<BOOL:${features_target_property}>:--features=$<JOIN:${features_target_property},$<COMMA>>>")
@@ -357,6 +358,9 @@ function(_add_cargo_build)
 
     set(global_joined_rustflags "$<JOIN:${global_rustflags_target_property}, >")
     set(global_rustflags_genex "$<$<BOOL:${global_rustflags_target_property}>:RUSTFLAGS=${global_joined_rustflags}>")
+    set(local_rustflags_delimiter "$<$<BOOL:${local_rustflags_target_property}>:-->")
+    set(local_rustflags_genex "$<$<BOOL:${local_rustflags_target_property}>:${local_rustflags_target_property}>")
+
 
     # Used to set a linker for a specific target-triple.
     set(cargo_target_linker_var "CARGO_TARGET_${_CORROSION_RUST_CARGO_TARGET_UPPER}_LINKER")
@@ -401,7 +405,7 @@ function(_add_cargo_build)
             "CORROSION_BUILD_DIR=${CMAKE_CURRENT_BINARY_DIR}"
             "CARGO_BUILD_RUSTC=${_CORROSION_RUSTC}"
         "${_CORROSION_CARGO}"
-            build
+            rustc
             ${cargo_target_option}
             ${_CORROSION_VERBOSE_OUTPUT_FLAG}
             # Global --features arguments added via corrosion_import_crate()
@@ -416,6 +420,9 @@ function(_add_cargo_build)
             ${cargo_profile}
             ${flag_args}
             ${flags_genex}
+            # Any arguments to cargo must be placed before this line
+            ${local_rustflags_delimiter}
+            ${local_rustflags_genex}
 
     # Copy crate artifacts to the binary dir
     COMMAND
@@ -610,6 +617,16 @@ function(corrosion_add_target_rustflags target_name rustflag)
     )
 endfunction()
 
+function(corrosion_add_target_local_rustflags target_name rustc_flag)
+    # Set Rustflags via `cargo rustc` which only affect the current crate, but not dependencies.
+    # Additional rustflags may be passed as optional parameters after rustflag.
+    set_property(
+            TARGET ${target_name}
+            APPEND
+            PROPERTY INTERFACE_CORROSION_LOCAL_RUSTFLAGS ${rustc_flag} ${ARGN}
+    )
+endfunction()
+
 function(corrosion_set_env_vars target_name env_var)
     # Additional environment variables may be passed as optional parameters after env_var.
     set_property(

test/custom_profiles/rust/Cargo.lock

@@ -11,3 +11,6 @@ corrosion_add_target_rustflags(rustflag-test-lib
         --cfg=test_rustflag_cfg2="$<IF:$<OR:$<CONFIG:Debug>,$<CONFIG:>>,debug,release>"
         "--cfg=test_rustflag_cfg3"
 )
+
+corrosion_add_target_local_rustflags(rustflag-test-lib "--cfg=test_local_rustflag1")
+corrosion_add_target_local_rustflags(rustflag-test-lib --cfg=test_local_rustflag2="value")

test/rustflags/CMakeLists.txt

@@ -5,6 +5,7 @@ license = "MIT"
 edition = "2018"
 
 [dependencies]
+some_dependency = { path = "some_dependency" }
 
 [lib]
 crate-type=["staticlib"]

test/rustflags/rust/Cargo.lock

@@ -0,0 +1,6 @@
+[package]
+name = "some_dependency"
+version = "0.1.0"
+license = "MIT"
+edition = "2018"
+

test/rustflags/rust/Cargo.toml

@@ -0,0 +1,10 @@
+//! Test that the local rustflags are only passed to the main crate and not to dependencies.
+#[cfg(test_local_rustflag1)]
+const _: [(); 1] = [(); 2];
+
+#[cfg(test_local_rustflag2 = "value")]
+const _: [(); 1] = [(); 2];
+
+pub fn some_function() -> u32 {
+    42
+}

test/rustflags/rust/some_dependency/Cargo.toml

@@ -27,7 +27,14 @@ pub extern "C" fn rust_second_function(name: *const c_char) {
 pub extern "C" fn rust_third_function(name: *const c_char) {
     let name = unsafe { std::ffi::CStr::from_ptr(name).to_str().unwrap() };
     println!("Hello, {}! I'm Rust again, third time the charm!", name);
+    assert_eq!(some_dependency::some_function(), 42);
 }
 
 #[cfg(not(test_rustflag_cfg3))]
 const _: [(); 1] = [(); 2];
+
+#[cfg(not(test_local_rustflag1))]
+const _: [(); 1] = [(); 2];
+
+#[cfg(not(test_local_rustflag2 = "value"))]
+const _: [(); 1] = [(); 2];