put From impl back, inform users of deprecation with a doc comment and a println

Notes:
- Trait implementations can't be deprecated, so had to use some other way.
- try_from is now an inherent function because From and TryFrom can't be
  implemented at the same time.

Author: antonilol

changelog.md

@@ -3,7 +3,7 @@ when upgrading from a version of rust-sdl2 to another.
 
 ### Next
 
-[PR #1413](https://github.com/Rust-SDL2/rust-sdl2/pull/1413) **BREAKING CHANGE** Replace `From` implementation of `SwapInterval` that could panic with `TryFrom`.
+[PR #1413](https://github.com/Rust-SDL2/rust-sdl2/pull/1413) Deprecate `From` implementation of `SwapInterval` that could panic, add `TryFrom`-like inherent function.
 
 [PR #1416](https://github.com/Rust-SDL2/rust-sdl2/pull/1416) Apply clippy fixes, fix deprecations and other code quality improvements.
 

src/sdl2/video.rs

@@ -592,10 +592,9 @@ pub enum SwapInterval {
     LateSwapTearing = -1,
 }
 
-impl TryFrom<i32> for SwapInterval {
-    type Error = SwapIntervalConversionError;
-
-    fn try_from(value: i32) -> Result<Self, Self::Error> {
+impl SwapInterval {
+    /// This function will be replaced later with a [`TryFrom`] implementation
+    pub fn try_from(value: i32) -> Result<Self, SwapIntervalConversionError> {
         Ok(match value {
             -1 => SwapInterval::LateSwapTearing,
             0 => SwapInterval::Immediate,
@@ -620,6 +619,17 @@ impl fmt::Display for SwapIntervalConversionError {
 
 impl Error for SwapIntervalConversionError {}
 
+impl From<i32> for SwapInterval {
+    /// This function is deprecated, use [`SwapInterval::try_from`] instead and handle the error.
+    fn from(i: i32) -> Self {
+        println!(
+            "SwapInterval::from is deprecated (could be called from .into()), \
+             use SwapInterval::try_from instead and handle the error"
+        );
+        Self::try_from(i).unwrap()
+    }
+}
+
 /// Represents orientation of a display.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 #[repr(i32)]