From 3712442fe3fca528831230ee4fbc68f3be138342 Mon Sep 17 00:00:00 2001
From: Nico Burns <nico@nicoburns.com>
Date: Wed, 8 Jan 2025 17:10:58 +1300
Subject: [PATCH] Reinstate 1.65 MSRV

---
 .github/workflows/ci.yml |  4 ++--
 Cargo.toml               |  2 +-
 src/style/dimension.rs   | 34 +++++++++++++++++++++++++++-------
 3 files changed, 30 insertions(+), 10 deletions(-)

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 1b008c663..2a20c91d7 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,13 +20,13 @@ jobs:
   # We only run `cargo build` (not `cargo test`) so as to avoid requiring dev-dependencies to build with the MSRV
   # version. Building is likely sufficient as runtime errors varying between rust versions is very unlikely.
   build-features-msrv:
-    name: "MSRV Build [Rust 1.83]"
+    name: "MSRV Build [Rust 1.65]"
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@master
         with:
-          toolchain: 1.83
+          toolchain: 1.65
       - run: cargo build
 
   build-features-debug:
diff --git a/Cargo.toml b/Cargo.toml
index ce22563fe..0e86eedb9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,7 @@ authors = [
     "Nico Burns <nico@nicoburns.com>",
 ]
 edition = "2021"
-rust-version = "1.83"
+rust-version = "1.65"
 include = ["src/**/*", "examples/**/*", "Cargo.toml", "README.md"]
 description = "A flexible UI layout library "
 repository = "https://github.com/DioxusLabs/taffy"
diff --git a/src/style/dimension.rs b/src/style/dimension.rs
index 70342c335..57e7f98eb 100644
--- a/src/style/dimension.rs
+++ b/src/style/dimension.rs
@@ -4,6 +4,26 @@ use crate::style_helpers::{
     FromFr, FromLength, FromPercent, TaffyAuto, TaffyFitContent, TaffyMaxContent, TaffyMinContent, TaffyZero,
 };
 
+// Note: these two functions are copied directly from the std (core) library. But by duplicating them
+// here we can reduce MSRV from 1.83 all the way down to 1.65 while retaining const constructors.
+
+/// Raw transmutation from `f32` to `u32`.
+const fn to_bits(val: f32) -> u32 {
+    // SAFETY: `u32` is a plain old datatype so we can always transmute to it.
+    #[allow(unsafe_code)]
+    unsafe {
+        core::mem::transmute(val)
+    }
+}
+/// Raw transmutation from `u32` to `f32`.
+const fn from_bits(v: u32) -> f32 {
+    // SAFETY: `u32` is a plain old datatype so we can always transmute from it.
+    #[allow(unsafe_code)]
+    unsafe {
+        core::mem::transmute(v)
+    }
+}
+
 /// A representation of a length as a compact 64-bit tagged pointer
 #[derive(Copy, Clone, PartialEq, Debug)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
@@ -46,7 +66,7 @@ impl CompactLength {
     /// to in their application (pixels, logical pixels, mm, etc) as they see fit.
     #[inline(always)]
     pub const fn length(val: f32) -> Self {
-        Self(((val.to_bits() as u64) << 32) | Self::LENGTH_TAG)
+        Self(((to_bits(val) as u64) << 32) | Self::LENGTH_TAG)
     }
 
     /// A percentage length relative to the size of the containing block.
@@ -54,7 +74,7 @@ impl CompactLength {
     /// **NOTE: percentages are represented as a f32 value in the range [0.0, 1.0] NOT the range [0.0, 100.0]**
     #[inline(always)]
     pub const fn percent(val: f32) -> Self {
-        Self(((val.to_bits() as u64) << 32) | Self::PERCENT_TAG)
+        Self(((to_bits(val) as u64) << 32) | Self::PERCENT_TAG)
     }
 
     /// A `calc()` value. The value passed here is treated as an opaque handle to
@@ -80,7 +100,7 @@ impl CompactLength {
     /// Spec: <https://www.w3.org/TR/css3-grid-layout/#fr-unit>
     #[inline(always)]
     pub const fn fr(val: f32) -> Self {
-        Self(((val.to_bits() as u64) << 32) | Self::FR_TAG)
+        Self(((to_bits(val) as u64) << 32) | Self::FR_TAG)
     }
 
     /// The size should be the "min-content" size.
@@ -108,7 +128,7 @@ impl CompactLength {
     /// by the min-content and max-content sizes.
     #[inline(always)]
     pub const fn fit_content_px(limit: f32) -> Self {
-        Self(((limit.to_bits() as u64) << 32) | Self::FIT_CONTENT_PX_TAG)
+        Self(((to_bits(limit) as u64) << 32) | Self::FIT_CONTENT_PX_TAG)
     }
 
     /// The size should be computed according to the "fit content" formula:
@@ -122,7 +142,7 @@ impl CompactLength {
     /// by the min-content and max-content sizes.
     #[inline(always)]
     pub const fn fit_content_percent(limit: f32) -> Self {
-        Self(((limit.to_bits() as u64) << 32) | Self::FIT_CONTENT_PERCENT_TAG)
+        Self(((to_bits(limit) as u64) << 32) | Self::FIT_CONTENT_PERCENT_TAG)
     }
 
     /// Get the primary tag
@@ -135,7 +155,7 @@ impl CompactLength {
     /// (e.g. the pixel value for a LENGTH variant)
     #[inline(always)]
     pub const fn value(self) -> f32 {
-        f32::from_bits((self.0 >> 32) as u32)
+        from_bits((self.0 >> 32) as u32)
     }
 
     /// Get the numeric value associated with the `CompactLength`
@@ -154,7 +174,7 @@ impl CompactLength {
     /// Returns true if the value is 0 px
     #[inline(always)]
     pub const fn is_zero(self) -> bool {
-        matches!(self, Self::ZERO)
+        self.0 == Self::ZERO.0
     }
 
     /// Returns true if the value is a length or percentage value