From 6c3792330d127a3d681e849b6557ea55605a8c20 Mon Sep 17 00:00:00 2001
From: Vinzenz Schroeter <vinzenz.f.s@gmail.com>
Date: Wed, 28 May 2025 12:25:30 +0200
Subject: [PATCH] do not overwrite header if content did not change

---
 build.rs | 55 +++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 39 insertions(+), 16 deletions(-)

diff --git a/build.rs b/build.rs
index 83e9641..615d00f 100644
--- a/build.rs
+++ b/build.rs
@@ -4,32 +4,55 @@
 //! the out directory. This can be used to use the build script as a command line tool from other
 //! build tools.
 
-use std::{env, fs::copy};
+use std::{env, fs};
 
 fn main() {
     let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
-    println!("cargo::rerun-if-changed={crate_dir}");
+    println!("cargo::rerun-if-changed={crate_dir}/src");
+    println!("cargo::rerun-if-changed={crate_dir}/build.rs");
+    println!("cargo::rerun-if-changed={crate_dir}/Cargo.toml");
+    println!("cargo::rerun-if-changed={crate_dir}/Cargo.lock");
+    println!("cargo::rerun-if-changed={crate_dir}/cbindgen.toml");
+    println!("cargo::rerun-if-env-changed=SERVICEPOINT_HEADER_OUT");
 
     let config =
         cbindgen::Config::from_file(crate_dir.clone() + "/cbindgen.toml")
             .unwrap();
-
     let output_dir = env::var("OUT_DIR").unwrap();
     let header_file = output_dir.clone() + "/servicepoint.h";
 
-    if let Ok(bindings) = cbindgen::generate_with_config(crate_dir, config) {
-        bindings.write_to_file(&header_file);
-
-        println!("cargo:include={output_dir}");
-
-        println!("cargo::rerun-if-env-changed=SERVICEPOINT_HEADER_OUT");
-        if let Ok(header_out) = env::var("SERVICEPOINT_HEADER_OUT") {
-            let header_copy = header_out + "/servicepoint.h";
-            println!("cargo:warning=Copying header to {header_copy}");
-            copy(header_file, &header_copy).unwrap();
-            println!("cargo::rerun-if-changed={header_copy}");
+    let bindings = match cbindgen::generate_with_config(crate_dir, config) {
+        Ok(bindings) => bindings,
+        Err(e) => {
+            eprintln!("cargo:warning=Servicepoint header could not be generated: {e:?}");
+            return;
         }
-    } else {
-        eprintln!("cargo:warning=Servicepoint header could not be generated");
+    };
+
+    bindings.write_to_file(&header_file);
+    println!("cargo:include={output_dir}");
+
+    if let Ok(header_out) = env::var("SERVICEPOINT_HEADER_OUT") {
+        let header_copy = header_out + "/servicepoint.h";
+        
+        if fs::exists(&header_copy).ok().unwrap_or(false) {
+            // check if content changed to prevent rebuild of dependents if not
+
+            let mut bindings_text = Vec::new();
+            bindings.write(&mut bindings_text);
+            
+            match fs::read(&header_copy) {
+                Ok(old_content) if old_content == bindings_text => {
+                    println!("cargo:warning=Header did not change, not updating timestamp");
+                    return;
+                }
+                _  => {}
+            };
+        }
+        
+        // file does not exist or is different
+        println!("cargo:warning=Copying header to {header_copy}");
+        fs::copy(header_file, &header_copy).unwrap();
+        println!("cargo::rerun-if-changed={header_copy}");
     }
 }