Rollup merge of #105843 - compiler-errors:sugg-const, r=lcnr

Suggest associated const on possible capitalization mistake

Suggest `i32::MAX` if we typed `i32::max` without making a function call.

Fixes #93844

2 files changed, 72 insertions, 0 deletions

diff --git a/src/test/ui/suggestions/assoc-ct-for-assoc-method.rs b/src/test/ui/suggestions/assoc-ct-for-assoc-method.rs
new file mode 100644
index 00000000000..fe222776989
--- /dev/null
+++ b/src/test/ui/suggestions/assoc-ct-for-assoc-method.rs
@@ -0,0 +1,25 @@
+struct MyS;
+
+impl MyS {
+    const FOO: i32 = 1;
+    fn foo() -> MyS {
+        MyS
+    }
+}
+
+fn main() {
+    let x: i32 = MyS::foo;
+    //~^ ERROR mismatched types
+    //~| HELP try referring to the
+
+    let z: i32 = i32::max;
+    //~^ ERROR mismatched types
+    //~| HELP try referring to the
+
+    // This example is still broken though... This is a hard suggestion to make,
+    // because we don't have access to the associated const probing code to make
+    // this suggestion where it's emitted, i.e. in trait selection.
+    let y: i32 = i32::max - 42;
+    //~^ ERROR cannot subtract
+    //~| HELP use parentheses
+}
diff --git a/src/test/ui/suggestions/assoc-ct-for-assoc-method.stderr b/src/test/ui/suggestions/assoc-ct-for-assoc-method.stderr
new file mode 100644
index 00000000000..afef38f1296
--- /dev/null
+++ b/src/test/ui/suggestions/assoc-ct-for-assoc-method.stderr
@@ -0,0 +1,47 @@
+error[E0308]: mismatched types
+  --> $DIR/assoc-ct-for-assoc-method.rs:11:18
+   |
+LL |     let x: i32 = MyS::foo;
+   |            ---   ^^^^^^^^ expected `i32`, found fn item
+   |            |
+   |            expected due to this
+   |
+   = note: expected type `i32`
+           found fn item `fn() -> MyS {MyS::foo}`
+help: try referring to the associated const `FOO` instead
+   |
+LL |     let x: i32 = MyS::FOO;
+   |                       ~~~
+
+error[E0308]: mismatched types
+  --> $DIR/assoc-ct-for-assoc-method.rs:15:18
+   |
+LL |     let z: i32 = i32::max;
+   |            ---   ^^^^^^^^ expected `i32`, found fn item
+   |            |
+   |            expected due to this
+   |
+   = note: expected type `i32`
+           found fn item `fn(i32, i32) -> i32 {<i32 as Ord>::max}`
+help: try referring to the associated const `MAX` instead
+   |
+LL |     let z: i32 = i32::MAX;
+   |                       ~~~
+
+error[E0369]: cannot subtract `{integer}` from `fn(i32, i32) -> i32 {<i32 as Ord>::max}`
+  --> $DIR/assoc-ct-for-assoc-method.rs:22:27
+   |
+LL |     let y: i32 = i32::max - 42;
+   |                  -------- ^ -- {integer}
+   |                  |
+   |                  fn(i32, i32) -> i32 {<i32 as Ord>::max}
+   |
+help: use parentheses to call this associated function
+   |
+LL |     let y: i32 = i32::max(/* i32 */, /* i32 */) - 42;
+   |                          ++++++++++++++++++++++
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0308, E0369.
+For more information about an error, try `rustc --explain E0308`.