Rollup merge of rust-lang#102068 - cjgillot:erased-lifetime-print, r=…

…eholk

Always print '_, even for erased lifetimes.

Explicit lifetime arguments are now the recommended syntax in rust 2018 and rust 2021.  This PR applies this discipline to rustc itself.

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -1088,17 +1088,9 @@ pub trait PrettyPrinter<'tcx>:
                         .generics_of(principal.def_id)
                         .own_substs_no_defaults(cx.tcx(), principal.substs);
 
-                    // Don't print `'_` if there's no unerased regions.
-                    let print_regions = args.iter().any(|arg| match arg.unpack() {
-                        GenericArgKind::Lifetime(r) => !r.is_erased(),
-                        _ => false,
-                    });
-                    let mut args = args.iter().cloned().filter(|arg| match arg.unpack() {
-                        GenericArgKind::Lifetime(_) => print_regions,
-                        _ => true,
-                    });
                     let mut projections = predicates.projection_bounds();
 
+                    let mut args = args.iter().cloned();
                     let arg0 = args.next();
                     let projection0 = projections.next();
                     if arg0.is_some() || projection0.is_some() {
@@ -1847,22 +1839,11 @@ impl<'tcx> Printer<'tcx> for FmtPrinter<'_, 'tcx> {
     ) -> Result<Self::Path, Self::Error> {
         self = print_prefix(self)?;
 
-        // Don't print `'_` if there's no unerased regions.
-        let print_regions = self.tcx.sess.verbose()
-            || args.iter().any(|arg| match arg.unpack() {
-                GenericArgKind::Lifetime(r) => !r.is_erased(),
-                _ => false,
-            });
-        let args = args.iter().cloned().filter(|arg| match arg.unpack() {
-            GenericArgKind::Lifetime(_) => print_regions,
-            _ => true,
-        });
-
-        if args.clone().next().is_some() {
+        if args.first().is_some() {
             if self.in_value {
                 write!(self, "::")?;
             }
-            self.generic_delimiters(|cx| cx.comma_sep(args))
+            self.generic_delimiters(|cx| cx.comma_sep(args.iter().cloned()))
         } else {
             Ok(self)
         }

src/test/codegen-units/item-collection/generic-impl.rs

@@ -30,11 +30,11 @@ pub struct LifeTimeOnly<'a> {
 
 impl<'a> LifeTimeOnly<'a> {
 
-    //~ MONO_ITEM fn LifeTimeOnly::foo
+    //~ MONO_ITEM fn LifeTimeOnly::<'_>::foo
     pub fn foo(&self) {}
-    //~ MONO_ITEM fn LifeTimeOnly::bar
+    //~ MONO_ITEM fn LifeTimeOnly::<'_>::bar
     pub fn bar(&'a self) {}
-    //~ MONO_ITEM fn LifeTimeOnly::baz
+    //~ MONO_ITEM fn LifeTimeOnly::<'_>::baz
     pub fn baz<'b>(&'b self) {}
 
     pub fn non_instantiated<T>(&self) {}

src/test/mir-opt/derefer_complex_case.main.Derefer.diff

@@ -3,15 +3,15 @@
 
   fn main() -> () {
       let mut _0: ();                      // return place in scope 0 at $DIR/derefer_complex_case.rs:+0:11: +0:11
-      let mut _1: std::slice::Iter<i32>;   // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
+      let mut _1: std::slice::Iter<'_, i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
       let mut _2: &[i32; 2];               // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
       let _3: [i32; 2];                    // in scope 0 at $DIR/derefer_complex_case.rs:+1:18: +1:26
-      let mut _4: std::slice::Iter<i32>;   // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
+      let mut _4: std::slice::Iter<'_, i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
       let mut _5: ();                      // in scope 0 at $DIR/derefer_complex_case.rs:+0:1: +2:2
       let _6: ();                          // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
       let mut _7: std::option::Option<&i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
-      let mut _8: &mut std::slice::Iter<i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
-      let mut _9: &mut std::slice::Iter<i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
+      let mut _8: &mut std::slice::Iter<'_, i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
+      let mut _9: &mut std::slice::Iter<'_, i32>; // in scope 0 at $DIR/derefer_complex_case.rs:+1:17: +1:26
       let mut _10: isize;                  // in scope 0 at $DIR/derefer_complex_case.rs:+1:5: +1:40
       let mut _11: !;                      // in scope 0 at $DIR/derefer_complex_case.rs:+1:5: +1:40
       let mut _13: i32;                    // in scope 0 at $DIR/derefer_complex_case.rs:+1:34: +1:37
@@ -53,10 +53,10 @@
           StorageLive(_9);                 // scope 1 at $DIR/derefer_complex_case.rs:+1:17: +1:26
           _9 = &mut _4;                    // scope 1 at $DIR/derefer_complex_case.rs:+1:17: +1:26
           _8 = &mut (*_9);                 // scope 1 at $DIR/derefer_complex_case.rs:+1:17: +1:26
-          _7 = <std::slice::Iter<i32> as Iterator>::next(move _8) -> bb3; // scope 1 at $DIR/derefer_complex_case.rs:+1:17: +1:26
+          _7 = <std::slice::Iter<'_, i32> as Iterator>::next(move _8) -> bb3; // scope 1 at $DIR/derefer_complex_case.rs:+1:17: +1:26
                                            // mir::Constant
                                            // + span: $DIR/derefer_complex_case.rs:6:17: 6:26
-                                           // + literal: Const { ty: for<'r> fn(&'r mut std::slice::Iter<i32>) -> Option<<std::slice::Iter<i32> as Iterator>::Item> {<std::slice::Iter<i32> as Iterator>::next}, val: Value(<ZST>) }
+                                           // + literal: Const { ty: for<'r> fn(&'r mut std::slice::Iter<'_, i32>) -> Option<<std::slice::Iter<'_, i32> as Iterator>::Item> {<std::slice::Iter<'_, i32> as Iterator>::next}, val: Value(<ZST>) }
       }
 
       bb3: {

src/test/mir-opt/early_otherwise_branch_soundness.no_downcast.EarlyOtherwiseBranch.diff

@@ -1,12 +1,12 @@
 - // MIR for `no_downcast` before EarlyOtherwiseBranch
 + // MIR for `no_downcast` after EarlyOtherwiseBranch
 
-  fn no_downcast(_1: &E) -> u32 {
+  fn no_downcast(_1: &E<'_>) -> u32 {
       debug e => _1;                       // in scope 0 at $DIR/early_otherwise_branch_soundness.rs:+0:16: +0:17
       let mut _0: u32;                     // return place in scope 0 at $DIR/early_otherwise_branch_soundness.rs:+0:26: +0:29
       let mut _2: isize;                   // in scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:20: +1:30
       let mut _3: isize;                   // in scope 0 at $DIR/early_otherwise_branch_soundness.rs:+1:12: +1:31
-      let mut _4: &E;                      // in scope 0 at $DIR/early_otherwise_branch_soundness.rs:+0:16: +0:17
+      let mut _4: &E<'_>;                  // in scope 0 at $DIR/early_otherwise_branch_soundness.rs:+0:16: +0:17
       scope 1 {
       }
 
@@ -16,7 +16,7 @@
       }
 
       bb1: {
-          _4 = deref_copy (((*_1) as Some).0: &E); // scope 1 at $DIR/early_otherwise_branch_soundness.rs:+1:12: +1:31
+          _4 = deref_copy (((*_1) as Some).0: &E<'_>); // scope 1 at $DIR/early_otherwise_branch_soundness.rs:+1:12: +1:31
           _2 = discriminant((*_4));        // scope 1 at $DIR/early_otherwise_branch_soundness.rs:+1:12: +1:31
           switchInt(move _2) -> [1_isize: bb2, otherwise: bb3]; // scope 1 at $DIR/early_otherwise_branch_soundness.rs:+1:12: +1:31
       }

src/test/mir-opt/funky_arms.float_to_exponential_common.ConstProp.diff

@@ -1,24 +1,24 @@
 - // MIR for `float_to_exponential_common` before ConstProp
 + // MIR for `float_to_exponential_common` after ConstProp
 
-  fn float_to_exponential_common(_1: &mut Formatter, _2: &T, _3: bool) -> Result<(), std::fmt::Error> {
+  fn float_to_exponential_common(_1: &mut Formatter<'_>, _2: &T, _3: bool) -> Result<(), std::fmt::Error> {
       debug fmt => _1;                     // in scope 0 at $DIR/funky_arms.rs:+0:35: +0:38
       debug num => _2;                     // in scope 0 at $DIR/funky_arms.rs:+0:60: +0:63
       debug upper => _3;                   // in scope 0 at $DIR/funky_arms.rs:+0:69: +0:74
       let mut _0: std::result::Result<(), std::fmt::Error>; // return place in scope 0 at $DIR/funky_arms.rs:+0:85: +0:91
       let _4: bool;                        // in scope 0 at $DIR/funky_arms.rs:+4:9: +4:19
-      let mut _5: &std::fmt::Formatter;    // in scope 0 at $DIR/funky_arms.rs:+4:22: +4:37
+      let mut _5: &std::fmt::Formatter<'_>; // in scope 0 at $DIR/funky_arms.rs:+4:22: +4:37
       let mut _7: std::option::Option<usize>; // in scope 0 at $DIR/funky_arms.rs:+13:30: +13:45
-      let mut _8: &std::fmt::Formatter;    // in scope 0 at $DIR/funky_arms.rs:+13:30: +13:45
+      let mut _8: &std::fmt::Formatter<'_>; // in scope 0 at $DIR/funky_arms.rs:+13:30: +13:45
       let mut _9: isize;                   // in scope 0 at $DIR/funky_arms.rs:+13:12: +13:27
-      let mut _11: &mut std::fmt::Formatter; // in scope 0 at $DIR/funky_arms.rs:+15:43: +15:46
+      let mut _11: &mut std::fmt::Formatter<'_>; // in scope 0 at $DIR/funky_arms.rs:+15:43: +15:46
       let mut _12: &T;                     // in scope 0 at $DIR/funky_arms.rs:+15:48: +15:51
       let mut _13: core::num::flt2dec::Sign; // in scope 0 at $DIR/funky_arms.rs:+15:53: +15:57
       let mut _14: u32;                    // in scope 0 at $DIR/funky_arms.rs:+15:59: +15:79
       let mut _15: u32;                    // in scope 0 at $DIR/funky_arms.rs:+15:59: +15:75
       let mut _16: usize;                  // in scope 0 at $DIR/funky_arms.rs:+15:59: +15:68
       let mut _17: bool;                   // in scope 0 at $DIR/funky_arms.rs:+15:81: +15:86
-      let mut _18: &mut std::fmt::Formatter; // in scope 0 at $DIR/funky_arms.rs:+17:46: +17:49
+      let mut _18: &mut std::fmt::Formatter<'_>; // in scope 0 at $DIR/funky_arms.rs:+17:46: +17:49
       let mut _19: &T;                     // in scope 0 at $DIR/funky_arms.rs:+17:51: +17:54
       let mut _20: core::num::flt2dec::Sign; // in scope 0 at $DIR/funky_arms.rs:+17:56: +17:60
       let mut _21: bool;                   // in scope 0 at $DIR/funky_arms.rs:+17:62: +17:67
@@ -38,10 +38,10 @@
           StorageLive(_4);                 // scope 0 at $DIR/funky_arms.rs:+4:9: +4:19
           StorageLive(_5);                 // scope 0 at $DIR/funky_arms.rs:+4:22: +4:37
           _5 = &(*_1);                     // scope 0 at $DIR/funky_arms.rs:+4:22: +4:37
-          _4 = Formatter::sign_plus(move _5) -> bb1; // scope 0 at $DIR/funky_arms.rs:+4:22: +4:37
+          _4 = Formatter::<'_>::sign_plus(move _5) -> bb1; // scope 0 at $DIR/funky_arms.rs:+4:22: +4:37
                                            // mir::Constant
                                            // + span: $DIR/funky_arms.rs:15:26: 15:35
-                                           // + literal: Const { ty: for<'r> fn(&'r Formatter) -> bool {Formatter::sign_plus}, val: Value(<ZST>) }
+                                           // + literal: Const { ty: for<'r> fn(&'r Formatter<'_>) -> bool {Formatter::<'_>::sign_plus}, val: Value(<ZST>) }
       }
 
       bb1: {
@@ -66,10 +66,10 @@
           StorageLive(_7);                 // scope 3 at $DIR/funky_arms.rs:+13:30: +13:45
           StorageLive(_8);                 // scope 3 at $DIR/funky_arms.rs:+13:30: +13:45
           _8 = &(*_1);                     // scope 3 at $DIR/funky_arms.rs:+13:30: +13:45
-          _7 = Formatter::precision(move _8) -> bb5; // scope 3 at $DIR/funky_arms.rs:+13:30: +13:45
+          _7 = Formatter::<'_>::precision(move _8) -> bb5; // scope 3 at $DIR/funky_arms.rs:+13:30: +13:45
                                            // mir::Constant
                                            // + span: $DIR/funky_arms.rs:24:34: 24:43
-                                           // + literal: Const { ty: for<'r> fn(&'r Formatter) -> Option<usize> {Formatter::precision}, val: Value(<ZST>) }
+                                           // + literal: Const { ty: for<'r> fn(&'r Formatter<'_>) -> Option<usize> {Formatter::<'_>::precision}, val: Value(<ZST>) }
       }
 
       bb5: {

src/test/mir-opt/issue_73223.main.SimplifyArmIdentity.diff

@@ -25,7 +25,7 @@
       let _24: &i32;                       // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
       let mut _25: &i32;                   // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
       let _26: &i32;                       // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-      let mut _27: std::option::Option<std::fmt::Arguments>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+      let mut _27: std::option::Option<std::fmt::Arguments<'_>>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
       scope 1 {
           debug split => _1;               // in scope 1 at $DIR/issue-73223.rs:+1:9: +1:14
           let _6: std::option::Option<i32>; // in scope 1 at $DIR/issue-73223.rs:+6:9: +6:14

src/test/mir-opt/issue_99325.main.mir_map.0.mir

@@ -26,7 +26,7 @@ fn main() -> () {
     let _19: &&[u8];                     // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let mut _20: &&[u8; 4];              // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let _21: &&[u8; 4];                  // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-    let mut _22: std::option::Option<std::fmt::Arguments>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+    let mut _22: std::option::Option<std::fmt::Arguments<'_>>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let _23: ();                         // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let mut _24: (&&[u8], &&[u8; 4]);    // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let mut _25: &&[u8];                 // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
@@ -46,7 +46,7 @@ fn main() -> () {
     let _40: &&[u8];                     // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let mut _41: &&[u8; 4];              // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let _42: &&[u8; 4];                  // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-    let mut _43: std::option::Option<std::fmt::Arguments>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+    let mut _43: std::option::Option<std::fmt::Arguments<'_>>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     scope 1 {
         debug left_val => _8;            // in scope 1 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         debug right_val => _9;           // in scope 1 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
@@ -128,7 +128,7 @@ fn main() -> () {
         _21 = &(*_9);                    // scope 2 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         _20 = &(*_21);                   // scope 2 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         StorageLive(_22);                // scope 2 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-        _22 = Option::<Arguments>::None; // scope 2 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _22 = Option::<Arguments<'_>>::None; // scope 2 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         _16 = core::panicking::assert_failed::<&[u8], &[u8; 4]>(move _17, move _18, move _20, move _22) -> bb19; // scope 2 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
                                          // mir::Constant
                                          // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL
@@ -237,7 +237,7 @@ fn main() -> () {
         _42 = &(*_30);                   // scope 4 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         _41 = &(*_42);                   // scope 4 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         StorageLive(_43);                // scope 4 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-        _43 = Option::<Arguments>::None; // scope 4 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+        _43 = Option::<Arguments<'_>>::None; // scope 4 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
         _37 = core::panicking::assert_failed::<&[u8], &[u8; 4]>(move _38, move _39, move _41, move _43) -> bb19; // scope 4 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
                                          // mir::Constant
                                          // + span: $SRC_DIR/core/src/macros/mod.rs:LL:COL

src/test/mir-opt/retag.array_casts.SimplifyCfg-elaborate-drops.after.mir

@@ -29,7 +29,7 @@ fn array_casts() -> () {
     let _31: &usize;                     // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let mut _32: &usize;                 // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     let _33: &usize;                     // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
-    let mut _34: std::option::Option<std::fmt::Arguments>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
+    let mut _34: std::option::Option<std::fmt::Arguments<'_>>; // in scope 0 at $SRC_DIR/core/src/macros/mod.rs:LL:COL
     scope 1 {
         debug x => _1;                   // in scope 1 at $DIR/retag.rs:+1:9: +1:14
         let _2: *mut usize;              // in scope 1 at $DIR/retag.rs:+2:9: +2:10

src/test/pretty/issue-4264.pp

@@ -34,10 +34,10 @@
                     ((::alloc::fmt::format as
                             for<'r> fn(Arguments<'r>) -> String {format})(((::core::fmt::Arguments::new_v1
                                 as
-                                fn(&[&'static str], &[ArgumentV1]) -> Arguments {Arguments::new_v1})((&([("test"
+                                fn(&[&'static str], &[ArgumentV1<'_>]) -> Arguments<'_> {Arguments::<'_>::new_v1})((&([("test"
                                             as &str)] as [&str; 1]) as &[&str; 1]),
-                            (&([] as [ArgumentV1; 0]) as &[ArgumentV1; 0])) as
-                            Arguments)) as String);
+                            (&([] as [ArgumentV1<'_>; 0]) as &[ArgumentV1<'_>; 0])) as
+                            Arguments<'_>)) as String);
                 (res as String)
             } as String);
     } as ())

src/test/ui/const-generics/issues/issue-83765.stderr

@@ -1,16 +1,16 @@
-error[E0391]: cycle detected when resolving instance `<LazyUpdim<T, { T::DIM }, DIM> as TensorDimension>::DIM`
+error[E0391]: cycle detected when resolving instance `<LazyUpdim<'_, T, { T::DIM }, DIM> as TensorDimension>::DIM`
   --> $DIR/issue-83765.rs:5:5
    |
 LL |     const DIM: usize;
    |     ^^^^^^^^^^^^^^^^
    |
-note: ...which requires computing candidate for `<LazyUpdim<T, { T::DIM }, DIM> as TensorDimension>`...
+note: ...which requires computing candidate for `<LazyUpdim<'_, T, { T::DIM }, DIM> as TensorDimension>`...
   --> $DIR/issue-83765.rs:4:1
    |
 LL | trait TensorDimension {
    | ^^^^^^^^^^^^^^^^^^^^^
-   = note: ...which again requires resolving instance `<LazyUpdim<T, { T::DIM }, DIM> as TensorDimension>::DIM`, completing the cycle
-note: cycle used when computing candidate for `<LazyUpdim<T, { T::DIM }, DIM> as TensorDimension>`
+   = note: ...which again requires resolving instance `<LazyUpdim<'_, T, { T::DIM }, DIM> as TensorDimension>::DIM`, completing the cycle
+note: cycle used when computing candidate for `<LazyUpdim<'_, T, { T::DIM }, DIM> as TensorDimension>`
   --> $DIR/issue-83765.rs:4:1
    |
 LL | trait TensorDimension {