From 16a2f5e28cee39a206d96e15480eceb881ece1bb Mon Sep 17 00:00:00 2001
From: Alexis Bourget <alexis.bourget@gmail.com>
Date: Wed, 22 Dec 2021 23:06:57 +0100
Subject: [PATCH] feat: Vec::try_with_capacity(_in)

---
 library/alloc/src/raw_vec.rs | 14 ++++++++++++++
 library/alloc/src/vec/mod.rs | 14 ++++++++++++++
 2 files changed, 28 insertions(+)

diff --git a/library/alloc/src/raw_vec.rs b/library/alloc/src/raw_vec.rs
index 3d38e73305a37..2ca46a6e306ab 100644
--- a/library/alloc/src/raw_vec.rs
+++ b/library/alloc/src/raw_vec.rs
@@ -132,6 +132,20 @@ impl<T, A: Allocator> RawVec<T, A> {
         Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
     }
 
+    /// Attempts to create a `RawVec` (on the system heap) with exactly the
+    /// capacity and alignment requirements for a `[T; capacity]`. This is
+    /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
+    /// zero-sized. Note that if `T` is zero-sized this means you will
+    /// *not* get a `RawVec` with the requested capacity.
+    ///
+    /// Parameterized over the choice of allocator for the returned `RawVec`.
+    #[inline]
+    pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
+        let mut raw_vec = Self::new_in(alloc);
+        raw_vec.try_reserve_exact(0, capacity)?;
+        Ok(raw_vec)
+    }
+
     /// Like `with_capacity_zeroed`, but parameterized over the choice
     /// of allocator for the returned `RawVec`.
     #[cfg(not(no_global_oom_handling))]
diff --git a/library/alloc/src/vec/mod.rs b/library/alloc/src/vec/mod.rs
index 16df293108017..b50bc0c1682ae 100644
--- a/library/alloc/src/vec/mod.rs
+++ b/library/alloc/src/vec/mod.rs
@@ -470,6 +470,13 @@ impl<T> Vec<T> {
         Self::with_capacity_in(capacity, Global)
     }
 
+    /// FIXME(poliorcetics): docs & tracking issue
+    #[inline]
+    #[unstable(feature = "try_with_capacity", issue = "91913")]
+    pub fn try_with_capacity(capacity: usize) -> Result<Self, TryReserveError> {
+        Self::try_with_capacity_in(capacity, Global)
+    }
+
     /// Creates a `Vec<T>` directly from the raw components of another vector.
     ///
     /// # Safety
@@ -609,6 +616,13 @@ impl<T, A: Allocator> Vec<T, A> {
         Vec { buf: RawVec::with_capacity_in(capacity, alloc), len: 0 }
     }
 
+    /// FIXME(poliorcetics): docs & tracking issue
+    #[inline]
+    #[unstable(feature = "try_with_capacity", issue = "91913")]
+    pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
+        Ok(Vec { buf: RawVec::try_with_capacity_in(capacity, alloc)?, len: 0 })
+    }
+
     /// Creates a `Vec<T, A>` directly from the raw components of another vector.
     ///
     /// # Safety