From 6b45f44d1fef6cb96ba7a3fca7ffdf702134f836 Mon Sep 17 00:00:00 2001
From: Filip Tibell <filip.tibell@gmail.com>
Date: Thu, 24 Apr 2025 18:53:17 +0200
Subject: [PATCH] Implement readLine in lune-std-stdio

---
 Cargo.lock                       |  1 +
 crates/lune-std-stdio/Cargo.toml |  1 +
 crates/lune-std-stdio/src/lib.rs | 36 ++++++++++++++++++++------------
 types/stdio.luau                 | 28 ++++++++++++++++---------
 4 files changed, 43 insertions(+), 23 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 90fb508..3e1eb86 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1776,6 +1776,7 @@ name = "lune-std-stdio"
 version = "0.1.2"
 dependencies = [
  "async-io",
+ "async-lock",
  "blocking",
  "dialoguer",
  "futures-lite",
diff --git a/crates/lune-std-stdio/Cargo.toml b/crates/lune-std-stdio/Cargo.toml
index e1ce87a..facaac9 100644
--- a/crates/lune-std-stdio/Cargo.toml
+++ b/crates/lune-std-stdio/Cargo.toml
@@ -17,6 +17,7 @@ mlua = { version = "0.10.3", features = ["luau", "error-send"] }
 mlua-luau-scheduler = { version = "0.0.2", path = "../mlua-luau-scheduler" }
 
 async-io = "2.4"
+async-lock = "3.4"
 blocking = "1.6"
 dialoguer = "0.11"
 futures-lite = "2.6"
diff --git a/crates/lune-std-stdio/src/lib.rs b/crates/lune-std-stdio/src/lib.rs
index 3137136..521973d 100644
--- a/crates/lune-std-stdio/src/lib.rs
+++ b/crates/lune-std-stdio/src/lib.rs
@@ -1,12 +1,16 @@
 #![allow(clippy::cargo_common_metadata)]
 
-use std::io::{stderr, stdin, stdout};
+use std::{
+    io::{stderr, stdin, stdout, Stdin},
+    sync::{Arc, LazyLock},
+};
 
 use mlua::prelude::*;
 use mlua_luau_scheduler::LuaSpawnExt;
 
+use async_lock::Mutex as AsyncMutex;
 use blocking::Unblock;
-use futures_lite::prelude::*;
+use futures_lite::{io::BufReader, prelude::*};
 
 use lune_utils::{
     fmt::{pretty_format_multi_value, ValueFormatConfig},
@@ -23,6 +27,12 @@ const FORMAT_CONFIG: ValueFormatConfig = ValueFormatConfig::new()
     .with_max_depth(4)
     .with_colors_enabled(false);
 
+static STDIN: LazyLock<Arc<AsyncMutex<BufReader<Unblock<Stdin>>>>> = LazyLock::new(|| {
+    let stdin = Unblock::new(stdin());
+    let reader = BufReader::new(stdin);
+    Arc::new(AsyncMutex::new(reader))
+});
+
 /**
     Creates the `stdio` standard library module.
 
@@ -37,6 +47,7 @@ pub fn module(lua: Lua) -> LuaResult<LuaTable> {
         .with_function("format", stdio_format)?
         .with_async_function("write", stdio_write)?
         .with_async_function("ewrite", stdio_ewrite)?
+        .with_async_function("readLine", stdio_read_line)?
         .with_async_function("readToEnd", stdio_read_to_end)?
         .with_async_function("prompt", stdio_prompt)?
         .build_readonly()
@@ -68,19 +79,18 @@ async fn stdio_ewrite(_: Lua, s: LuaString) -> LuaResult<()> {
     Ok(())
 }
 
-/*
-    FUTURE: Figure out how to expose some kind of "readLine" function using a buffered reader.
-
-    This is a bit tricky since we would want to be able to use **both** readLine and readToEnd
-    in the same script, doing something like readLine, readLine, readToEnd from lua, and
-    having that capture the first two lines and then read the rest of the input.
-*/
+async fn stdio_read_line(lua: Lua, (): ()) -> LuaResult<LuaString> {
+    let mut string = String::new();
+    let mut handle = STDIN.lock_arc().await;
+    handle.read_line(&mut string).await?;
+    lua.create_string(&string)
+}
 
 async fn stdio_read_to_end(lua: Lua, (): ()) -> LuaResult<LuaString> {
-    let mut input = Vec::new();
-    let mut stdin = Unblock::new(stdin());
-    stdin.read_to_end(&mut input).await?;
-    lua.create_string(&input)
+    let mut buffer = Vec::new();
+    let mut handle = STDIN.lock_arc().await;
+    handle.read_to_end(&mut buffer).await?;
+    lua.create_string(&buffer)
 }
 
 async fn stdio_prompt(lua: Lua, options: PromptOptions) -> LuaResult<PromptResult> {
diff --git a/types/stdio.luau b/types/stdio.luau
index e6e88a4..06ebc27 100644
--- a/types/stdio.luau
+++ b/types/stdio.luau
@@ -1,13 +1,4 @@
-export type Color =
-	"reset"
-	| "black"
-	| "red"
-	| "green"
-	| "yellow"
-	| "blue"
-	| "purple"
-	| "cyan"
-	| "white"
+export type Color = "reset" | "black" | "red" | "green" | "yellow" | "blue" | "purple" | "cyan" | "white"
 export type Style = "reset" | "bold" | "dim"
 
 type PromptFn = (
@@ -59,6 +50,9 @@ end
 	stdio.write("All on the same line")
 	stdio.ewrite("\nAnd some error text, too")
 
+	-- Reading a single line from stdin
+	local line = stdio.readLine()
+
 	-- Reading the entire input from stdin
 	local input = stdio.readToEnd()
 	```
@@ -146,6 +140,20 @@ function stdio.write(s: string) end
 ]=]
 function stdio.ewrite(s: string) end
 
+--[=[
+    @within Stdio
+    @tag must_use
+
+    Reads a single line from stdin.
+
+    If stdin is closed, returns all input up until its closure.
+
+    @return The input from stdin
+]=]
+function stdio.readLine(): string
+	return nil :: any
+end
+
 --[=[
     @within Stdio
     @tag must_use