Make some manual impl Default derived

Some caught by the new lint introduced in the next commit. Others noticed manually.

Author: estebank

compiler/rustc_ast/src/ast.rs

@@ -31,7 +31,7 @@ use rustc_data_structures::sync::Lrc;
 use rustc_macros::{Decodable, Encodable, HashStable_Generic};
 pub use rustc_span::AttrId;
 use rustc_span::source_map::{Spanned, respan};
-use rustc_span::{DUMMY_SP, ErrorGuaranteed, Ident, Span, Symbol, kw, sym};
+use rustc_span::{ErrorGuaranteed, Ident, Span, Symbol, kw, sym};
 use thin_vec::{ThinVec, thin_vec};
 
 pub use crate::format::*;
@@ -387,22 +387,15 @@ impl GenericParam {
 
 /// Represents lifetime, type and const parameters attached to a declaration of
 /// a function, enum, trait, etc.
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Default)]
 pub struct Generics {
     pub params: ThinVec<GenericParam>,
     pub where_clause: WhereClause,
     pub span: Span,
 }
 
-impl Default for Generics {
-    /// Creates an instance of `Generics`.
-    fn default() -> Generics {
-        Generics { params: ThinVec::new(), where_clause: Default::default(), span: DUMMY_SP }
-    }
-}
-
 /// A where-clause in a definition.
-#[derive(Clone, Encodable, Decodable, Debug)]
+#[derive(Clone, Encodable, Decodable, Debug, Default)]
 pub struct WhereClause {
     /// `true` if we ate a `where` token.
     ///
@@ -419,12 +412,6 @@ impl WhereClause {
     }
 }
 
-impl Default for WhereClause {
-    fn default() -> WhereClause {
-        WhereClause { has_where_token: false, predicates: ThinVec::new(), span: DUMMY_SP }
-    }
-}
-
 /// A single predicate in a where-clause.
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct WherePredicate {

compiler/rustc_lint/src/unused.rs

@@ -1023,19 +1023,14 @@ declare_lint! {
     "`if`, `match`, `while` and `return` do not need parentheses"
 }
 
+#[derive(Default)]
 pub(crate) struct UnusedParens {
     with_self_ty_parens: bool,
     /// `1 as (i32) < 2` parses to ExprKind::Lt
     /// `1 as i32 < 2` parses to i32::<2[missing angle bracket]
     parens_in_cast_in_lt: Vec<ast::NodeId>,
 }
 
-impl Default for UnusedParens {
-    fn default() -> Self {
-        Self { with_self_ty_parens: false, parens_in_cast_in_lt: Vec::new() }
-    }
-}
-
 impl_lint_pass!(UnusedParens => [UNUSED_PARENS]);
 
 impl UnusedDelimLint for UnusedParens {

compiler/rustc_session/src/config.rs

@@ -168,9 +168,10 @@ pub struct CoverageOptions {
 }
 
 /// Controls whether branch coverage or MC/DC coverage is enabled.
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
+#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Default)]
 pub enum CoverageLevel {
     /// Instrument for coverage at the MIR block level.
+    #[default]
     Block,
     /// Also instrument branch points (includes block coverage).
     Branch,
@@ -195,12 +196,6 @@ pub enum CoverageLevel {
     Mcdc,
 }
 
-impl Default for CoverageLevel {
-    fn default() -> Self {
-        Self::Block
-    }
-}
-
 /// Settings for `-Z instrument-xray` flag.
 #[derive(Clone, Copy, Debug, Default, PartialEq, Eq, Hash)]
 pub struct InstrumentXRay {

library/core/src/ascii/ascii_char.rs

@@ -54,12 +54,13 @@ use crate::{assert_unsafe_precondition, fmt};
 /// [chart]: https://www.unicode.org/charts/PDF/U0000.pdf
 /// [NIST FIPS 1-2]: https://nvlpubs.nist.gov/nistpubs/Legacy/FIPS/fipspub1-2-1977.pdf
 /// [NamesList]: https://www.unicode.org/Public/15.0.0/ucd/NamesList.txt
-#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[derive(Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Default)]
 #[unstable(feature = "ascii_char", issue = "110998")]
 #[repr(u8)]
 pub enum AsciiChar {
     /// U+0000 (The default variant)
     #[unstable(feature = "ascii_char_variants", issue = "110998")]
+    #[default]
     Null = 0,
     /// U+0001
     #[unstable(feature = "ascii_char_variants", issue = "110998")]

library/core/src/default.rs

@@ -2,8 +2,6 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use crate::ascii::Char as AsciiChar;
-
 /// A trait for giving a type a useful default value.
 ///
 /// Sometimes, you want to fall back to some kind of default value, and
@@ -163,7 +161,6 @@ macro_rules! default_impl {
 default_impl! { (), (), "Returns the default value of `()`" }
 default_impl! { bool, false, "Returns the default value of `false`" }
 default_impl! { char, '\x00', "Returns the default value of `\\x00`" }
-default_impl! { AsciiChar, AsciiChar::Null, "Returns the default value of `Null`" }
 
 default_impl! { usize, 0, "Returns the default value of `0`" }
 default_impl! { u8, 0, "Returns the default value of `0`" }

library/std/src/panicking.rs

@@ -81,7 +81,9 @@ extern "C" fn __rust_foreign_exception() -> ! {
     rtabort!("Rust cannot catch foreign exceptions");
 }
 
+#[derive(Default)]
 enum Hook {
+    #[default]
     Default,
     Custom(Box<dyn Fn(&PanicHookInfo<'_>) + 'static + Sync + Send>),
 }
@@ -96,13 +98,6 @@ impl Hook {
     }
 }
 
-impl Default for Hook {
-    #[inline]
-    fn default() -> Hook {
-        Hook::Default
-    }
-}
-
 static HOOK: RwLock<Hook> = RwLock::new(Hook::Default);
 
 /// Registers a custom panic hook, replacing the previously registered hook.