From 8b45d74ecf49a34b8b126394a3cb8251f4c0e741 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 19 Aug 2016 17:30:07 -0400
Subject: [PATCH 1/2] Add syntex::with_extra_stack helper

---
 syntex/src/lib.rs   |  3 +++
 syntex/src/stack.rs | 63 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)
 create mode 100644 syntex/src/stack.rs

diff --git a/syntex/src/lib.rs b/syntex/src/lib.rs
index 6f7352fe..40a71444 100644
--- a/syntex/src/lib.rs
+++ b/syntex/src/lib.rs
@@ -27,6 +27,9 @@ use syntex_syntax::ptr::P;
 mod error;
 pub use error::Error;
 
+mod stack;
+pub use stack::with_extra_stack;
+
 pub type Pass = fn(ast::Crate) -> ast::Crate;
 
 pub struct Registry {
diff --git a/syntex/src/stack.rs b/syntex/src/stack.rs
new file mode 100644
index 00000000..05dc4606
--- /dev/null
+++ b/syntex/src/stack.rs
@@ -0,0 +1,63 @@
+use std::env;
+use std::ffi::OsStr;
+use std::ops::Drop;
+use std::thread;
+
+const STACK_ENV_VAR: &'static str = "RUST_MIN_STACK";
+const EXTRA_STACK: &'static str = "16777216"; // 16 MB
+
+/// Runs a function in a thread with extra stack space (16 MB or
+/// `$RUST_MIN_STACK` if set).
+///
+/// The Rust parser uses a lot of stack space so codegen sometimes requires more
+/// than is available by default.
+///
+/// ```
+/// syntex::with_extra_stack(move || {
+///     let mut reg = syntex::Registry::new();
+///     reg.add_decorator(/* ... */);
+///     reg.expand("", src, dst)
+/// })
+/// ```
+///
+/// This function runs with a 16 MB stack by default but a different value can
+/// be set by the RUST_MIN_STACK environment variable.
+pub fn with_extra_stack<F, T>(f: F) -> T
+    where F: Send + 'static + FnOnce() -> T,
+          T: Send + 'static
+{
+    let _tmp_env = set_if_unset(STACK_ENV_VAR, EXTRA_STACK);
+
+    thread::spawn(f).join().unwrap()
+}
+
+fn set_if_unset<K, V>(k: K, v: V) -> TmpEnv<K>
+    where K: AsRef<OsStr>,
+          V: AsRef<OsStr>,
+{
+    match env::var(&k) {
+        Ok(_) => TmpEnv::WasAlreadySet,
+        Err(_) => {
+            env::set_var(&k, v);
+            TmpEnv::WasNotSet(k)
+        }
+    }
+}
+
+#[must_use]
+enum TmpEnv<K>
+    where K: AsRef<OsStr>,
+{
+    WasAlreadySet,
+    WasNotSet(K),
+}
+
+impl<K> Drop for TmpEnv<K>
+    where K: AsRef<OsStr>,
+{
+    fn drop(&mut self) {
+        if let TmpEnv::WasNotSet(ref k) = *self {
+            env::remove_var(k);
+        }
+    }
+}

From 8337663a1f1d9cb05bbd72ee5bc2f0319f7e794e Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Fri, 19 Aug 2016 17:44:40 -0400
Subject: [PATCH 2/2] Ignore with_extra_stack example

---
 syntex/src/stack.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/syntex/src/stack.rs b/syntex/src/stack.rs
index 05dc4606..2d96a6ae 100644
--- a/syntex/src/stack.rs
+++ b/syntex/src/stack.rs
@@ -12,7 +12,7 @@ const EXTRA_STACK: &'static str = "16777216"; // 16 MB
 /// The Rust parser uses a lot of stack space so codegen sometimes requires more
 /// than is available by default.
 ///
-/// ```
+/// ```rust,ignore
 /// syntex::with_extra_stack(move || {
 ///     let mut reg = syntex::Registry::new();
 ///     reg.add_decorator(/* ... */);