feat(macros): allow Android domain parts to have underscores

.changes/android-package-underscores.md

@@ -0,0 +1,6 @@
+---
+"tao-macros": patch
+"tao": patch
+---
+
+Allow Android domain names to include `_1` as escaped `_` characters - required because `_` is the separator for domain parts.

tao-macros/src/lib.rs

@@ -101,7 +101,7 @@ impl Parse for AndroidFnInput {
 /// 5. List of extra types your Rust function expects. Pass empty array if the function doesn't need any arugments.
 ///   - If your function takes an arguments as reference with a lifetime tied to the [`JNIEnv`], it should use `'local` as the lifetime name as it is the
 ///     lifetime name generated by the macro.
-/// Note that all rust functions should expect the first two parameters to be [`JNIEnv`] and [`JClass`] so make sure they are imported into scope).
+///     Note that all rust functions should expect the first two parameters to be [`JNIEnv`] and [`JClass`] so make sure they are imported into scope).
 /// 6. (Optional) Return type of your rust function.
 ///   - If your function returns a reference with a lifetime tied to the [`JNIEnv`], it should use `'local` as the lifetime name as it is the
 ///     lifetime name generated by the macro.
@@ -202,7 +202,7 @@ pub fn android_fn(tokens: TokenStream) -> TokenStream {
   } = tokens;
 
   let domain = domain.to_string();
-  let package = package.to_string().replace('_', "_1").replace('-', "_1");
+  let package = package.to_string().replace('_', "_1");
   let class = class.to_string();
   let args = args
     .into_iter()
@@ -273,6 +273,11 @@ impl Parse for GeneratePackageNameInput {
 /// 1. snake_case representation of the reversed domain of the app.
 /// 2. snake_case representation of the package name.
 ///
+/// Note that `_` is the separator for the domain parts.
+/// For instance the `com.tauri.app` identifier should be represented as
+/// `generate_package_name!(com_tauri, app)`.
+/// To escape the `_` character you can use `_1` which aligns with the default NDK implementation.
+///
 /// ## Example
 ///
 /// ```
@@ -295,8 +300,15 @@ pub fn generate_package_name(tokens: TokenStream) -> TokenStream {
   let tokens = parse_macro_input!(tokens as GeneratePackageNameInput);
   let GeneratePackageNameInput { domain, package } = tokens;
 
-  let domain = domain.to_string().replace('_', "/");
-  let package = package.to_string().replace('-', "_");
+  // note that this character is invalid in an identifier so it's safe to use as replacement
+  const TEMP_ESCAPE_UNDERSCORE_REPLACEMENT: &str = "<";
+
+  let domain = domain
+    .to_string()
+    .replace("_1", TEMP_ESCAPE_UNDERSCORE_REPLACEMENT)
+    .replace('_', "/")
+    .replace(TEMP_ESCAPE_UNDERSCORE_REPLACEMENT, "_");
+  let package = package.to_string();
 
   let path = format!("{}/{}", domain, package);
   let litstr = LitStr::new(&path, proc_macro2::Span::call_site());