message: Dump environment setup during build
diff: @@ -285,6 +285,17 @@ static MANIFEST_DIR: Lazy<PathBuf> = Lazy::new(|| PathBuf::from(env::var_os("CAR
  static SRC_DIR: Lazy<PathBuf> = Lazy::new(|| MANIFEST_DIR.join("src"));
  static SRC_CPP_DIR: Lazy<PathBuf> = Lazy::new(|| MANIFEST_DIR.join("src_cpp"));
  +static ENV_VARS: [&str; 8] = [
  + "OPENCV_HEADER_DIR",
  + "OPENCV_PACKAGE_NAME",
  + "OPENCV_PKGCONFIG_NAME",
  + "OPENCV_LINK_LIBS",
  + "OPENCV_LINK_PATHS",
  + "OPENCV_INCLUDE_PATHS",
  + "PKG_CONFIG_PATH",
  + "VCPKG_ROOT",
  +];
  +
  #[derive(Debug)]
  struct Library {
  pub pkg_name: String,
  @@ -615,12 +626,9 @@ fn build_compiler(opencv_header_dir: &Path) -> cc::Build {
  }
  fn build_wrapper(opencv_header_dir: &Path) -> Result<()> {
  - println!("cargo:rerun-if-env-changed=OPENCV_HEADER_DIR");
  - println!("cargo:rerun-if-env-changed=OPENCV_PACKAGE_NAME");
  - println!("cargo:rerun-if-env-changed=OPENCV_PKGCONFIG_NAME");
  - println!("cargo:rerun-if-env-changed=OPENCV_LINK_LIBS");
  - println!("cargo:rerun-if-env-changed=OPENCV_LINK_PATHS");
  - println!("cargo:rerun-if-env-changed=OPENCV_INCLUDE_PATHS");
  + for &v in ENV_VARS.iter() {
  + println!("cargo:rerun-if-env-changed={}", v);
  + }
  let include_exts = &[OsStr::new("cpp"), OsStr::new("hpp")];
  for entry in SRC_CPP_DIR.read_dir()?.map(|e| e.unwrap()) {
  @@ -690,6 +698,10 @@ fn main() -> Result<()> {
  if features != 1 {
  panic!("Please select exactly one of the features: opencv-32, opencv-34, opencv-4");
  }
  + eprintln!("=== Environment configuration:");
  + for &v in ENV_VARS.iter() {
  + eprintln!("=== {} = {:?}", v, env::var_os(v));
  + }
  let opencv = if cfg!(feature = "docs-only") {
  Library::probe_from_paths("opencv", "", "", "")?
  } else {
  