feat(core): add From impl for RenderResult with closure coercion

2 files changed, 31 insertions, 1 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2bc0318..962d048 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -310,6 +310,27 @@ None
 
     The macro is re-exported as `mingling::macros::r_append` and included in `mingling::prelude::*`.
 
+13. **[`core`]** **[`macros`]** Added `From<F>` implementation for `RenderResult` where `F: FnOnce() -> RenderResult`. This enables `RenderResult` to be constructed from a closure or function pointer that returns a `RenderResult`, enabling ergonomic composition of render buffers.
+
+    This is particularly useful with the `#[buffer]` extension attribute, which creates a separate buffer function that can be called from within a `#[renderer(buffer)]` function using `r_append!`:
+
+    ```rust
+    use mingling::macros::{buffer, r_append, r_println};
+
+    // A standalone buffer function
+    #[buffer]
+    fn print_sth() {
+        r_println!("ok");
+    }
+
+    #[renderer(buffer)]
+    fn render_greet(_: ResultGreet) {
+        r_append!(print_sth);  // appends `a`'s RenderResult content into `p`'s buffer
+    }
+    ```
+
+    Under the hood, `r_append!` (when used in implicit buffer mode inside a `#[buffer]` function) calls `append_other` on the current render buffer. The `From<F>` implementation allows the buffer function's return value (a `RenderResult`) to be seamlessly converted into the parent's buffer via `append_other`. This enables clean separation of render logic into reusable buffer functions that can be composed together.
+
 #### **BREAKING CHANGES** (API CHANGES):
 
 1. **[`macros:renderer`]** **[`macros:help`]** Removed `r_println!` and `r_print!` macros from being implicitly injected by `#[renderer]` and `#[help]` macros. These macros still exist, but must now be used **explicitly** — either with an explicit buffer argument, or via the `#[buffer]` extension attribute that re-enables implicit buffer injection.
diff --git a/mingling_core/src/renderer/render_result.rs b/mingling_core/src/renderer/render_result.rs
index a495857..c38522a 100644
--- a/mingling_core/src/renderer/render_result.rs
+++ b/mingling_core/src/renderer/render_result.rs
@@ -47,6 +47,15 @@ pub enum RenderResultMode {
     Stderr = 1,
 }
 
+impl<F> From<F> for RenderResult
+where
+    F: FnOnce() -> RenderResult,
+{
+    fn from(value: F) -> Self {
+        value()
+    }
+}
+
 impl Write for RenderResult {
     fn write(&mut self, buf: &[u8]) -> std::io::Result<usize> {
         let s = std::str::from_utf8(buf).map_err(|_| {
@@ -233,7 +242,7 @@ impl RenderResult {
     /// src.append_to_buffer("Hello", RenderResultMode::Stdout);
     /// src.append_to_buffer(" Error", RenderResultMode::Stderr);
     ///
-    /// dest.append_otehr(src);
+    /// dest.append_other(src);
     /// assert_eq!(dest.to_string(), "Hello Error");
     /// ```
     pub fn append_other(&mut self, other: impl Into<RenderResult>) {