Suggest minimal subset features in incomplete_features lint

Author: JohnTitor

compiler/rustc_lint/src/builtin.rs

@@ -2288,12 +2288,20 @@ impl EarlyLintPass for IncompleteFeatures {
                             n, n,
                         ));
                     }
+                    if HAS_MIN_FEATURES.contains(&name) {
+                        builder.help(&format!(
+                            "consider using `min_{}` instead, which is more stable and complete",
+                            name,
+                        ));
+                    }
                     builder.emit();
                 })
             });
     }
 }
 
+const HAS_MIN_FEATURES: &[Symbol] = &[sym::const_generics, sym::specialization];
+
 declare_lint! {
     /// The `invalid_value` lint detects creating a value that is not valid,
     /// such as a NULL reference.

src/test/ui/array-slice-vec/match_arr_unknown_len.stderr

@@ -6,6 +6,7 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 error[E0308]: mismatched types
   --> $DIR/match_arr_unknown_len.rs:6:9

src/test/ui/associated-types/defaults-specialization.stderr

@@ -6,6 +6,7 @@ LL | #![feature(associated_type_defaults, specialization)]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: consider using `min_specialization` instead, which is more stable and complete
 
 error[E0053]: method `make` has an incompatible type for trait
   --> $DIR/defaults-specialization.rs:19:18

src/test/ui/binding/const-param.stderr

@@ -6,6 +6,7 @@ LL | #![feature(const_generics)]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 error[E0158]: const parameters cannot be referenced in patterns
   --> $DIR/const-param.rs:7:9

src/test/ui/coherence/coherence-inherited-assoc-ty-cycle-err.stderr

@@ -6,6 +6,7 @@ LL | #![feature(specialization)]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #31844 <https://github.com/rust-lang/rust/issues/31844> for more information
+   = help: consider using `min_specialization` instead, which is more stable and complete
 
 error[E0391]: cycle detected when building specialization graph of trait `Trait`
   --> $DIR/coherence-inherited-assoc-ty-cycle-err.rs:9:1

src/test/ui/const-generics/defaults/wrong-order.full.stderr

@@ -14,6 +14,7 @@ LL | #![cfg_attr(full, feature(const_generics))]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 error: aborting due to previous error; 1 warning emitted
 

src/test/ui/const-generics/issues/issue-56445.full.stderr

@@ -6,6 +6,7 @@ LL | #![cfg_attr(full, feature(const_generics))]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 error[E0771]: use of non-static lifetime `'a` in const generic
   --> $DIR/issue-56445.rs:9:26

src/test/ui/const-generics/issues/issue-60818-struct-constructors.full.stderr

@@ -6,6 +6,7 @@ LL | #![cfg_attr(full, feature(const_generics))]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 warning: 1 warning emitted
 

src/test/ui/const-generics/issues/issue-61336-1.full.stderr

@@ -6,6 +6,7 @@ LL | #![cfg_attr(full, feature(const_generics))]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 warning: 1 warning emitted
 

src/test/ui/const-generics/issues/issue-61336-2.full.stderr

@@ -6,6 +6,7 @@ LL | #![cfg_attr(full, feature(const_generics))]
    |
    = note: `#[warn(incomplete_features)]` on by default
    = note: see issue #44580 <https://github.com/rust-lang/rust/issues/44580> for more information
+   = help: consider using `min_const_generics` instead, which is more stable and complete
 
 error[E0277]: the trait bound `T: Copy` is not satisfied
   --> $DIR/issue-61336-2.rs:10:5