Prevent build.rs rerunning unnecessarily on all source changes

serde/build.rs

@@ -6,6 +6,8 @@ use std::str::{self, FromStr};
 // opening a GitHub issue if your build environment requires some way to enable
 // these cfgs other than by executing our build script.
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
     let minor = match rustc_minor_version() {
         Some(minor) => minor,
         None => return,

serde_derive/build.rs

@@ -6,6 +6,8 @@ use std::str;
 // opening a GitHub issue if your build environment requires some way to enable
 // these cfgs other than by executing our build script.
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
     let minor = match rustc_minor_version() {
         Some(minor) => minor,
         None => return,

serde_derive_internals/build.rs

@@ -1,6 +1,9 @@
 use std::path::Path;
 
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-changed=src/mod.rs");
+
     // Sometimes on Windows the git checkout does not correctly wire up the
     // symlink from serde_derive_internals/src to serde_derive/src/internals.
     // When this happens we'll just build based on relative paths within the git

serde_test/build.rs

@@ -6,6 +6,8 @@ use std::str::{self, FromStr};
 // opening a GitHub issue if your build environment requires some way to enable
 // these cfgs other than by executing our build script.
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
     let minor = match rustc_minor_version() {
         Some(minor) => minor,
         None => return,

test_suite/build.rs

@@ -19,6 +19,8 @@ fn has_cargo_expand() -> bool {
 }
 
 fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
     if cfg!(feature = "expandtest") && has_cargo_expand() {
         println!("cargo:rustc-cfg=expandtest");
     }