Introduce CFG.change_detection bool flag

Adds `cargo:rerun-if-changed=<path>` for all files used by the bridge if the `CFG.change_detection` is `true`.

Author: nyurik

README.md

@@ -242,12 +242,12 @@ cxx-build = "1.0"
 // build.rs
 
 fn main() {
+    cxx_build::CFG.change_detection = true;
     cxx_build::bridge("src/main.rs")  // returns a cc::Build
         .file("src/demo.cc")
         .std("c++11")
         .compile("cxxbridge-demo");
 
-    println!("cargo:rerun-if-changed=src/main.rs");
     println!("cargo:rerun-if-changed=src/demo.cc");
     println!("cargo:rerun-if-changed=include/demo.h");
 }

book/src/build/cargo.md

@@ -36,12 +36,12 @@ set up any additional source files and compiler flags as normal.
 // build.rs
 
 fn main() {
+    cxx_build::CFG.change_detection = true;
     cxx_build::bridge("src/main.rs")  // returns a cc::Build
         .file("src/demo.cc")
         .std("c++11")
         .compile("cxxbridge-demo");
 
-    println!("cargo:rerun-if-changed=src/main.rs");
     println!("cargo:rerun-if-changed=src/demo.cc");
     println!("cargo:rerun-if-changed=include/demo.h");
 }

book/src/tutorial.md

@@ -201,11 +201,11 @@ build.
 // build.rs
 
 fn main() {
+    cxx_build::CFG.change_detection = true;
     cxx_build::bridge("src/main.rs")
         .file("src/blobstore.cc")
         .compile("cxx-demo");
 
-    println!("cargo:rerun-if-changed=src/main.rs");
     println!("cargo:rerun-if-changed=src/blobstore.cc");
     println!("cargo:rerun-if-changed=include/blobstore.h");
 }

demo/build.rs

@@ -1,10 +1,10 @@
 fn main() {
+    cxx_build::CFG.change_detection = true;
     cxx_build::bridge("src/main.rs")
         .file("src/blobstore.cc")
         .std("c++14")
         .compile("cxxbridge-demo");
 
-    println!("cargo:rerun-if-changed=src/main.rs");
     println!("cargo:rerun-if-changed=src/blobstore.cc");
     println!("cargo:rerun-if-changed=include/blobstore.h");
 }

gen/build/src/cfg.rs

@@ -14,6 +14,8 @@ pub struct Cfg<'a> {
     pub exported_header_links: Vec<&'a str>,
     /// See [`CFG.doxygen`][CFG#cfgdoxygen].
     pub doxygen: bool,
+    /// See [`CFG.change_detection`][CFG#cfgchange_detection].
+    pub change_detection: bool,
     marker: PhantomData<*const ()>, // !Send + !Sync
 }
 

gen/build/src/lib.rs

@@ -14,12 +14,12 @@
 //! // build.rs
 //!
 //! fn main() {
+//!     cxx_build::CFG.change_detection = true;
 //!     cxx_build::bridge("src/main.rs")
 //!         .file("src/demo.cc")
 //!         .std("c++11")
 //!         .compile("cxxbridge-demo");
 //!
-//!     println!("cargo:rerun-if-changed=src/main.rs");
 //!     println!("cargo:rerun-if-changed=src/demo.cc");
 //!     println!("cargo:rerun-if-changed=include/demo.h");
 //! }
@@ -397,6 +397,9 @@ fn generate_bridge(prj: &Project, build: &mut Build, rust_source_file: &Path) ->
         doxygen: CFG.doxygen,
         ..Opt::default()
     };
+    if CFG.change_detection {
+        println!("cargo:rerun-if-changed={}", rust_source_file.display());
+    }
     let generated = gen::generate_from_path(rust_source_file, &opt);
     let ref rel_path = paths::local_relative_path(rust_source_file);
 

src/lib.rs

@@ -249,12 +249,12 @@
 //! // build.rs
 //!
 //! fn main() {
+//!     cxx_build::CFG.change_detection = true;
 //!     cxx_build::bridge("src/main.rs")  // returns a cc::Build
 //!         .file("src/demo.cc")
 //!         .std("c++11")
 //!         .compile("cxxbridge-demo");
 //!
-//!     println!("cargo:rerun-if-changed=src/main.rs");
 //!     println!("cargo:rerun-if-changed=src/demo.cc");
 //!     println!("cargo:rerun-if-changed=include/demo.h");
 //! }