Change wording of suggestion to add missing match arm

Author: estebank

compiler/rustc_mir_build/src/thir/pattern/check_match.rs

@@ -336,7 +336,7 @@ fn check_for_bindings_named_same_as_variants(
                     let ty_path = cx.tcx.def_path_str(edef.did);
                     let mut err = lint.build(&format!(
                         "pattern binding `{}` is named the same as one \
-                                        of the variants of the type `{}`",
+                         of the variants of the type `{}`",
                         ident, ty_path
                     ));
                     err.code(error_code!(E0170));
@@ -508,6 +508,7 @@ fn non_exhaustive_match<'p, 'tcx>(
     // informative.
     let mut err;
     let pattern;
+    let mut patterns_len = 0;
     if is_empty_match && !non_empty_enum {
         err = create_e0004(
             cx.tcx.sess,
@@ -523,6 +524,7 @@ fn non_exhaustive_match<'p, 'tcx>(
             format!("non-exhaustive patterns: {} not covered", joined_patterns),
         );
         err.span_label(sp, pattern_not_covered_label(&witnesses, &joined_patterns));
+        patterns_len = witnesses.len();
         pattern = if witnesses.len() < 4 {
             witnesses
                 .iter()
@@ -622,12 +624,29 @@ fn non_exhaustive_match<'p, 'tcx>(
         _ => {}
     }
 
-    let msg = "ensure that all possible cases are being handled, possibly by adding wildcards \
-        or more match arms";
+    let msg = format!(
+        "ensure that all possible cases are being handled by adding a match arm with a wildcard \
+         pattern{}{}",
+        if patterns_len > 1 && patterns_len < 4 && suggestion.is_some() {
+            ", a match arm with multiple or-patterns"
+        } else {
+            // we are either not suggesting anything, or suggesting `_`
+            ""
+        },
+        match patterns_len {
+            // non-exhaustive enum case
+            0 if suggestion.is_some() => " as shown",
+            0 => "",
+            1 if suggestion.is_some() => " or an explicit pattern as shown",
+            1 => " or an explicit pattern",
+            _ if suggestion.is_some() => " as shown, or multiple match arms",
+            _ => " or multiple match arms",
+        },
+    );
     if let Some((span, sugg)) = suggestion {
-        err.span_suggestion_verbose(span, msg, sugg, Applicability::HasPlaceholders);
+        err.span_suggestion_verbose(span, &msg, sugg, Applicability::HasPlaceholders);
     } else {
-        err.help(msg);
+        err.help(&msg);
     }
     err.emit();
 }

src/test/ui/closures/2229_closure_analysis/match/issue-88331.stderr

@@ -10,7 +10,7 @@ note: `Opcode` defined here
 LL | pub struct Opcode(pub u8);
    |            ^^^^^^
    = note: the matched value is of type `Opcode`
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         Opcode::OP1 => unimplemented!(),
 LL ~         Opcode(0_u8) | Opcode(2_u8..=u8::MAX) => todo!(),
@@ -28,7 +28,7 @@ note: `Opcode2` defined here
 LL | pub struct Opcode2(Opcode);
    |            ^^^^^^^
    = note: the matched value is of type `Opcode2`
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~         Opcode2::OP2=> unimplemented!(),
 LL ~         Opcode2(Opcode(0_u8)) | Opcode2(Opcode(2_u8..=u8::MAX)) => todo!(),

src/test/ui/closures/2229_closure_analysis/match/non-exhaustive-match.stderr

@@ -10,7 +10,7 @@ note: `L1` defined here
 LL | enum L1 { A, B }
    |      --      ^ not covered
    = note: the matched value is of type `L1`
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL |     let _b = || { match l1 { L1::A => (), B => todo!() } };
    |                                         ++++++++++++++
@@ -27,7 +27,7 @@ note: `E1` defined here
 LL | pub enum E1 {}
    | ^^^^^^^^^^^^^^
    = note: the matched value is of type `E1`, which is marked as non-exhaustive
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern as shown
    |
 LL ~     let _d = || { match e1 {
 LL +         _ => todo!(),
@@ -46,7 +46,7 @@ note: `E2` defined here
 LL | pub enum E2 { A, B }
    | ^^^^^^^^^^^^^^^^^^^^
    = note: the matched value is of type `E2`, which is marked as non-exhaustive
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL |     let _e = || { match e2 { E2::A => (), E2::B => (), _ => todo!() } };
    |                                                      ++++++++++++++

src/test/ui/closures/2229_closure_analysis/match/pattern-matching-should-fail.stderr

@@ -5,7 +5,7 @@ LL |     let c1 = || match x { };
    |                       ^
    |
    = note: the matched value is of type `u8`
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern as shown
    |
 LL ~     let c1 = || match x {
 LL +         _ => todo!(),

src/test/ui/error-codes/E0004-2.stderr

@@ -19,7 +19,7 @@ LL | |     Some(#[stable(feature = "rust1", since = "1.0.0")] T),
 LL | | }
    | |_-
    = note: the matched value is of type `Option<i32>`
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern, a match arm with multiple or-patterns as shown, or multiple match arms
    |
 LL ~     match x {
 LL +         None | Some(_) => todo!(),

src/test/ui/error-codes/E0004.stderr

@@ -12,7 +12,7 @@ LL | enum Terminator {
 LL |     HastaLaVistaBaby,
    |     ^^^^^^^^^^^^^^^^ not covered
    = note: the matched value is of type `Terminator`
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         Terminator::TalkToMyHand => {}
 LL +         HastaLaVistaBaby => todo!()

src/test/ui/feature-gates/feature-gate-precise_pointer_size_matching.stderr

@@ -7,7 +7,7 @@ LL |     match 0usize {
    = note: the matched value is of type `usize`
    = note: `usize` does not have a fixed maximum value, so a wildcard `_` is necessary to match exhaustively
    = help: add `#![feature(precise_pointer_size_matching)]` to the crate attributes to enable precise `usize` matching
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         0..=usize::MAX => {}
 LL +         _ => todo!()
@@ -22,7 +22,7 @@ LL |     match 0isize {
    = note: the matched value is of type `isize`
    = note: `isize` does not have a fixed maximum value, so a wildcard `_` is necessary to match exhaustively
    = help: add `#![feature(precise_pointer_size_matching)]` to the crate attributes to enable precise `isize` matching
-help: ensure that all possible cases are being handled, possibly by adding wildcards or more match arms
+help: ensure that all possible cases are being handled by adding a match arm with a wildcard pattern or an explicit pattern as shown
    |
 LL ~         isize::MIN..=isize::MAX => {}
 LL +         _ => todo!()