Rollup merge of #132708 - estebank:const-as-binding, r=Nadrieril

Point at `const` definition when used instead of a binding in a `let` statement

Modify `PatKind::InlineConstant` to be `ExpandedConstant` standing in not only for inline `const` blocks but also for `const` items. This allows us to track named `const`s used in patterns when the pattern is a single binding. When we detect that there is a refutable pattern involving a `const` that could have been a binding instead, we point at the `const` item, and suggest renaming. We do this for both `let` bindings and `match` expressions missing a catch-all arm if there's at least one single binding pattern referenced.

After:

```
error[E0005]: refutable pattern in local binding
  --> $DIR/bad-pattern.rs:19:13
   |
LL |     const PAT: u32 = 0;
   |     -------------- missing patterns are not covered because `PAT` is interpreted as a constant pattern, not a new variable
...
LL |         let PAT = v1;
   |             ^^^ pattern `1_u32..=u32::MAX` not covered
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
   = note: the matched value is of type `u32`
help: introduce a variable instead
   |
LL |         let PAT_var = v1;
   |             ~~~~~~~
```

Before:

```
error[E0005]: refutable pattern in local binding
  --> $DIR/bad-pattern.rs:19:13
   |
LL |         let PAT = v1;
   |             ^^^
   |             |
   |             pattern `1_u32..=u32::MAX` not covered
   |             missing patterns are not covered because `PAT` is interpreted as a constant pattern, not a new variable
   |             help: introduce a variable instead: `PAT_var`
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
   = note: the matched value is of type `u32`
```

CC #132582.

2 files changed, 84 insertions, 0 deletions

diff --git a/tests/ui/pattern/usefulness/match-arm-statics-2.stderr b/tests/ui/pattern/usefulness/match-arm-statics-2.stderr
index e4dd35a5995..60b4fcca286 100644
--- a/tests/ui/pattern/usefulness/match-arm-statics-2.stderr
+++ b/tests/ui/pattern/usefulness/match-arm-statics-2.stderr
@@ -3,8 +3,20 @@ error[E0004]: non-exhaustive patterns: `(true, false)` not covered
    |
 LL |     match (true, false) {
    |           ^^^^^^^^^^^^^ pattern `(true, false)` not covered
+LL |
+LL |         TRUE_TRUE => (),
+   |         --------- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `TRUE_TRUE`
    |
    = note: the matched value is of type `(bool, bool)`
+note: constant `TRUE_TRUE` defined here
+  --> $DIR/match-arm-statics-2.rs:14:1
+   |
+LL | const TRUE_TRUE: (bool, bool) = (true, true);
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         TRUE_TRUE_var => (),
+   |                  ++++
 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 ~         (false, true) => (),
diff --git a/tests/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr b/tests/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr
index a8786d02414..0a3991fe3d1 100644
--- a/tests/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr
+++ b/tests/ui/pattern/usefulness/slice-patterns-exhaustiveness.stderr
@@ -199,8 +199,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ patterns `&[]` and `&[_, _, ..]` not covered
+LL |
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 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 ~         CONST => {},
@@ -212,8 +224,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ patterns `&[]` and `&[_, _, ..]` not covered
+LL |
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 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 ~         &[false] => {},
@@ -225,8 +249,20 @@ error[E0004]: non-exhaustive patterns: `&[]` and `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ patterns `&[]` and `&[_, _, ..]` not covered
+...
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 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 ~         CONST => {},
@@ -238,8 +274,20 @@ error[E0004]: non-exhaustive patterns: `&[_, _, ..]` not covered
    |
 LL |     match s {
    |           ^ pattern `&[_, _, ..]` not covered
+...
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 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 ~         CONST => {},
@@ -251,8 +299,20 @@ error[E0004]: non-exhaustive patterns: `&[false]` not covered
    |
 LL |     match s {
    |           ^ pattern `&[false]` not covered
+...
+LL |         CONST => {}
+   |         ----- this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST`
    |
    = note: the matched value is of type `&[bool]`
+note: constant `CONST` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:88:5
+   |
+LL |     const CONST: &[bool] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST_var => {}
+   |              ++++
 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 ~         &[_, _, ..] => {},
@@ -264,8 +324,20 @@ error[E0004]: non-exhaustive patterns: `&[false]` not covered
    |
 LL |     match s1 {
    |           ^^ pattern `&[false]` not covered
+LL |
+LL |         CONST1 => {}
+   |         ------ this pattern doesn't introduce a new catch-all binding, but rather pattern matches against the value of constant `CONST1`
    |
    = note: the matched value is of type `&[bool; 1]`
+note: constant `CONST1` defined here
+  --> $DIR/slice-patterns-exhaustiveness.rs:124:5
+   |
+LL |     const CONST1: &[bool; 1] = &[true];
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^
+help: if you meant to introduce a binding, use a different name
+   |
+LL |         CONST1_var => {}
+   |               ++++
 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 ~         CONST1 => {},