Add example with generated cfg option

Author: Undin

build.rs

@@ -24,6 +24,8 @@ fn main() {
         }
     ");
     println!("cargo:rustc-env=GENERATED_ENV={}", gen_dir.display());
+
+    println!("cargo:rustc-cfg=has_generated_feature")
 }
 
 fn generate_file<P: AsRef<Path>>(path: P, text: &[u8]) {

examples/generated_cfg.rs

@@ -0,0 +1,5 @@
+use code_generation_example::function_under_cfg;
+
+fn main() {
+    function_under_cfg();
+}

src/disabled.rs

@@ -0,0 +1,3 @@
+pub fn function_under_cfg() {
+    println!("'has_generated_feature' is disabled")
+}

src/enabled.rs

@@ -0,0 +1,3 @@
+pub fn function_under_cfg() {
+    println!("'has_generated_feature' is enabled")
+}

src/lib.rs

@@ -1,2 +1,12 @@
 include!(concat!(env!("OUT_DIR"), "/hello.rs"));
 include!(concat!(env!("GENERATED_ENV"), "/hello2.rs"));
+
+#[cfg(not(has_generated_feature))]
+mod disabled;
+#[cfg(has_generated_feature)]
+mod enabled;
+
+#[cfg(not(has_generated_feature))]
+pub use disabled::function_under_cfg;
+#[cfg(has_generated_feature)]
+pub use enabled::function_under_cfg;