Rollup merge of #61654 - Electron-libre:use_slice_patterns_in_rustc, r=oli-obk,Centril

use pattern matching for slices destructuring

refs #61542

Use slices pattern where it seems to make sense .

7 files changed, 56 insertions, 67 deletions

diff --git a/src/libsyntax/diagnostics/plugin.rs b/src/libsyntax/diagnostics/plugin.rs
index 9f01b9b9f9b..98351048c35 100644
--- a/src/libsyntax/diagnostics/plugin.rs
+++ b/src/libsyntax/diagnostics/plugin.rs
@@ -33,8 +33,10 @@ pub fn expand_diagnostic_used<'cx>(ecx: &'cx mut ExtCtxt<'_>,
                                    span: Span,
                                    token_tree: &[TokenTree])
                                    -> Box<dyn MacResult+'cx> {
-    let code = match (token_tree.len(), token_tree.get(0)) {
-        (1, Some(&TokenTree::Token(Token { kind: token::Ident(code, _), .. }))) => code,
+    let code = match token_tree {
+        [
+            TokenTree::Token(Token { kind: token::Ident(code, _), .. })
+        ] => code,
         _ => unreachable!()
     };
 
@@ -66,22 +68,19 @@ pub fn expand_register_diagnostic<'cx>(ecx: &'cx mut ExtCtxt<'_>,
                                        span: Span,
                                        token_tree: &[TokenTree])
                                        -> Box<dyn MacResult+'cx> {
-    let (code, description) = match (
-        token_tree.len(),
-        token_tree.get(0),
-        token_tree.get(1),
-        token_tree.get(2)
-    ) {
-        (1, Some(&TokenTree::Token(Token { kind: token::Ident(code, _), .. })), None, None) => {
-            (code, None)
+    let (code, description) = match  token_tree {
+        [
+            TokenTree::Token(Token { kind: token::Ident(code, _), .. })
+        ] => {
+            (*code, None)
+        },
+        [
+            TokenTree::Token(Token { kind: token::Ident(code, _), .. }),
+            TokenTree::Token(Token { kind: token::Comma, .. }),
+            TokenTree::Token(Token { kind: token::Literal(token::Lit { symbol, .. }), ..})
+        ] => {
+            (*code, Some(*symbol))
         },
-        (3, Some(&TokenTree::Token(Token { kind: token::Ident(code, _), .. })),
-            Some(&TokenTree::Token(Token { kind: token::Comma, .. })),
-            Some(&TokenTree::Token(Token {
-                kind: token::Literal(token::Lit { symbol, .. }), ..
-            }))) => {
-            (code, Some(symbol))
-        }
         _ => unreachable!()
     };
 
diff --git a/src/libsyntax/parse/mod.rs b/src/libsyntax/parse/mod.rs
index cde35681988..dd96c63ab0e 100644
--- a/src/libsyntax/parse/mod.rs
+++ b/src/libsyntax/parse/mod.rs
@@ -424,48 +424,38 @@ mod tests {
                 string_to_stream("macro_rules! zip (($a)=>($a))".to_string()).trees().collect();
             let tts: &[TokenTree] = &tts[..];
 
-            match (tts.len(), tts.get(0), tts.get(1), tts.get(2), tts.get(3)) {
-                (
-                    4,
-                    Some(&TokenTree::Token(Token {
-                        kind: token::Ident(name_macro_rules, false), ..
-                    })),
-                    Some(&TokenTree::Token(Token { kind: token::Not, .. })),
-                    Some(&TokenTree::Token(Token { kind: token::Ident(name_zip, false), .. })),
-                    Some(&TokenTree::Delimited(_, macro_delim, ref macro_tts)),
-                )
-                if name_macro_rules == sym::macro_rules && name_zip.as_str() == "zip" => {
+            match tts {
+                [
+                    TokenTree::Token(Token { kind: token::Ident(name_macro_rules, false), .. }),
+                    TokenTree::Token(Token { kind: token::Not, .. }),
+                    TokenTree::Token(Token { kind: token::Ident(name_zip, false), .. }),
+                    TokenTree::Delimited(_, macro_delim,  macro_tts)
+                ]
+                if name_macro_rules == &sym::macro_rules && name_zip.as_str() == "zip" => {
                     let tts = &macro_tts.trees().collect::<Vec<_>>();
-                    match (tts.len(), tts.get(0), tts.get(1), tts.get(2)) {
-                        (
-                            3,
-                            Some(&TokenTree::Delimited(_, first_delim, ref first_tts)),
-                            Some(&TokenTree::Token(Token { kind: token::FatArrow, .. })),
-                            Some(&TokenTree::Delimited(_, second_delim, ref second_tts)),
-                        )
-                        if macro_delim == token::Paren => {
+                    match &tts[..] {
+                        [
+                            TokenTree::Delimited(_, first_delim, first_tts),
+                            TokenTree::Token(Token { kind: token::FatArrow, .. }),
+                            TokenTree::Delimited(_, second_delim, second_tts),
+                        ]
+                        if macro_delim == &token::Paren => {
                             let tts = &first_tts.trees().collect::<Vec<_>>();
-                            match (tts.len(), tts.get(0), tts.get(1)) {
-                                (
-                                    2,
-                                    Some(&TokenTree::Token(Token { kind: token::Dollar, .. })),
-                                    Some(&TokenTree::Token(Token {
-                                        kind: token::Ident(name, false), ..
-                                    })),
-                                )
-                                if first_delim == token::Paren && name.as_str() == "a" => {},
+                            match &tts[..] {
+                                [
+                                    TokenTree::Token(Token { kind: token::Dollar, .. }),
+                                    TokenTree::Token(Token { kind: token::Ident(name, false), .. }),
+                                ]
+                                if first_delim == &token::Paren && name.as_str() == "a" => {},
                                 _ => panic!("value 3: {:?} {:?}", first_delim, first_tts),
                             }
                             let tts = &second_tts.trees().collect::<Vec<_>>();
-                            match (tts.len(), tts.get(0), tts.get(1)) {
-                                (
-                                    2,
-                                    Some(&TokenTree::Token(Token { kind: token::Dollar, .. })),
-                                    Some(&TokenTree::Token(Token {
-                                        kind: token::Ident(name, false), ..
-                                    })),
-                                )
-                                if second_delim == token::Paren && name.as_str() == "a" => {},
+                            match &tts[..] {
+                                [
+                                    TokenTree::Token(Token { kind: token::Dollar, .. }),
+                                    TokenTree::Token(Token { kind: token::Ident(name, false), .. }),
+                                ]
+                                if second_delim == &token::Paren && name.as_str() == "a" => {},
                                 _ => panic!("value 4: {:?} {:?}", second_delim, second_tts),
                             }
                         },
diff --git a/src/libsyntax_ext/deriving/cmp/ord.rs b/src/libsyntax_ext/deriving/cmp/ord.rs
index b25a9e4c50f..844865d57c7 100644
--- a/src/libsyntax_ext/deriving/cmp/ord.rs
+++ b/src/libsyntax_ext/deriving/cmp/ord.rs
@@ -82,8 +82,8 @@ pub fn cs_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_>) -> P<
         // }
 
         let new = {
-            let other_f = match (other_fs.len(), other_fs.get(0)) {
-                (1, Some(o_f)) => o_f,
+            let other_f = match other_fs {
+                [o_f] => o_f,
                 _ => cx.span_bug(span, "not exactly 2 arguments in `derive(Ord)`"),
             };
 
diff --git a/src/libsyntax_ext/deriving/cmp/partial_eq.rs b/src/libsyntax_ext/deriving/cmp/partial_eq.rs
index 6172f27261e..732bb234389 100644
--- a/src/libsyntax_ext/deriving/cmp/partial_eq.rs
+++ b/src/libsyntax_ext/deriving/cmp/partial_eq.rs
@@ -25,8 +25,8 @@ pub fn expand_deriving_partial_eq(cx: &mut ExtCtxt<'_>,
              -> P<Expr>
     {
         let op = |cx: &mut ExtCtxt<'_>, span: Span, self_f: P<Expr>, other_fs: &[P<Expr>]| {
-            let other_f = match (other_fs.len(), other_fs.get(0)) {
-                (1, Some(o_f)) => o_f,
+            let other_f = match other_fs {
+                [o_f] => o_f,
                 _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialEq)`"),
             };
 
diff --git a/src/libsyntax_ext/deriving/cmp/partial_ord.rs b/src/libsyntax_ext/deriving/cmp/partial_ord.rs
index 3980741f252..a30a7d78222 100644
--- a/src/libsyntax_ext/deriving/cmp/partial_ord.rs
+++ b/src/libsyntax_ext/deriving/cmp/partial_ord.rs
@@ -143,8 +143,8 @@ pub fn cs_partial_cmp(cx: &mut ExtCtxt<'_>, span: Span, substr: &Substructure<'_
                 // }
 
                 let new = {
-                    let other_f = match (other_fs.len(), other_fs.get(0)) {
-                        (1, Some(o_f)) => o_f,
+                    let other_f = match other_fs {
+                        [o_f] => o_f,
                                 _ => {
                                     cx.span_bug(span,
                                         "not exactly 2 arguments in `derive(PartialOrd)`")
@@ -193,8 +193,8 @@ fn cs_op(less: bool,
     };
 
     let par_cmp = |cx: &mut ExtCtxt<'_>, span, self_f: P<Expr>, other_fs: &[P<Expr>], default| {
-        let other_f = match (other_fs.len(), other_fs.get(0)) {
-            (1, Some(o_f)) => o_f,
+        let other_f = match other_fs {
+            [o_f] => o_f,
             _ => cx.span_bug(span, "not exactly 2 arguments in `derive(PartialOrd)`"),
         };
 
diff --git a/src/libsyntax_ext/deriving/hash.rs b/src/libsyntax_ext/deriving/hash.rs
index e7f99d45782..7ad04aebf6e 100644
--- a/src/libsyntax_ext/deriving/hash.rs
+++ b/src/libsyntax_ext/deriving/hash.rs
@@ -52,8 +52,8 @@ pub fn expand_deriving_hash(cx: &mut ExtCtxt<'_>,
 }
 
 fn hash_substructure(cx: &mut ExtCtxt<'_>, trait_span: Span, substr: &Substructure<'_>) -> P<Expr> {
-    let state_expr = match (substr.nonself_args.len(), substr.nonself_args.get(0)) {
-        (1, Some(o_f)) => o_f,
+    let state_expr = match &substr.nonself_args {
+        &[o_f] => o_f,
         _ => {
             cx.span_bug(trait_span,
                         "incorrect number of arguments in `derive(Hash)`")
diff --git a/src/libsyntax_ext/trace_macros.rs b/src/libsyntax_ext/trace_macros.rs
index 6c74f77ff1f..512513e9b41 100644
--- a/src/libsyntax_ext/trace_macros.rs
+++ b/src/libsyntax_ext/trace_macros.rs
@@ -16,11 +16,11 @@ pub fn expand_trace_macros(cx: &mut ExtCtxt<'_>,
                                        feature_gate::EXPLAIN_TRACE_MACROS);
     }
 
-    match (tt.len(), tt.first()) {
-        (1, Some(TokenTree::Token(token))) if token.is_keyword(kw::True) => {
+    match tt {
+        [TokenTree::Token(token)] if token.is_keyword(kw::True) => {
             cx.set_trace_macros(true);
         }
-        (1, Some(TokenTree::Token(token))) if token.is_keyword(kw::False) => {
+        [TokenTree::Token(token)] if token.is_keyword(kw::False) => {
             cx.set_trace_macros(false);
         }
         _ => cx.span_err(sp, "trace_macros! accepts only `true` or `false`"),