Auto merge of #42227 - ollie27:into_to_from, r=<try>

Convert Intos to Froms.

This is a resubmission of #42129 without `impl<T> From<Vec<T>> for Box<[T]>`.

Author: bors

src/libcollections/string.rs

@@ -2088,9 +2088,9 @@ impl From<Box<str>> for String {
 }
 
 #[stable(feature = "box_from_str", since = "1.18.0")]
-impl Into<Box<str>> for String {
-    fn into(self) -> Box<str> {
-        self.into_boxed_str()
+impl From<String> for Box<str> {
+    fn from(s: String) -> Box<str> {
+        s.into_boxed_str()
     }
 }
 

src/libstd/ffi/c_str.rs

@@ -517,9 +517,9 @@ impl From<Box<CStr>> for CString {
 }
 
 #[stable(feature = "box_from_c_string", since = "1.18.0")]
-impl Into<Box<CStr>> for CString {
-    fn into(self) -> Box<CStr> {
-        self.into_boxed_c_str()
+impl From<CString> for Box<CStr> {
+    fn from(s: CString) -> Box<CStr> {
+        s.into_boxed_c_str()
     }
 }
 

src/libstd/ffi/os_str.rs

@@ -543,9 +543,9 @@ impl From<Box<OsStr>> for OsString {
 }
 
 #[stable(feature = "box_from_os_string", since = "1.18.0")]
-impl Into<Box<OsStr>> for OsString {
-    fn into(self) -> Box<OsStr> {
-        self.into_boxed_os_str()
+impl From<OsString> for Box<OsStr> {
+    fn from(s: OsString) -> Box<OsStr> {
+        s.into_boxed_os_str()
     }
 }
 

src/libstd/path.rs

@@ -1349,9 +1349,9 @@ impl From<Box<Path>> for PathBuf {
 }
 
 #[stable(feature = "box_from_path_buf", since = "1.18.0")]
-impl Into<Box<Path>> for PathBuf {
-    fn into(self) -> Box<Path> {
-        self.into_boxed_path()
+impl From<PathBuf> for Box<Path> {
+    fn from(p: PathBuf) -> Box<Path> {
+        p.into_boxed_path()
     }
 }