Improve dead code analysis for structs and traits defined locally

Author: mu001999

compiler/rustc_incremental/messages.ftl

@@ -99,6 +99,4 @@ incremental_unrecognized_depnode = unrecognized `DepNode` variant: {$name}
 
 incremental_unrecognized_depnode_label = dep-node label `{$label}` not recognized
 
-incremental_write_dep_graph = failed to write dependency graph to `{$path}`: {$err}
-
 incremental_write_new = failed to write {$name} to `{$path}`: {$err}

compiler/rustc_incremental/src/errors.rs

@@ -272,13 +272,6 @@ pub struct LoadDepGraph {
     pub err: std::io::Error,
 }
 
-#[derive(Diagnostic)]
-#[diag(incremental_write_dep_graph)]
-pub struct WriteDepGraph<'a> {
-    pub path: &'a Path,
-    pub err: std::io::Error,
-}
-
 #[derive(Diagnostic)]
 #[diag(incremental_move_dep_graph)]
 pub struct MoveDepGraph<'a> {

compiler/rustc_passes/src/dead.rs

@@ -4,7 +4,6 @@ use crate::layout;
 pub(crate) trait QueryContext {
     type Def: layout::Def;
     type Ref: layout::Ref;
-    type Scope: Copy;
 }
 
 #[cfg(test)]
@@ -28,7 +27,6 @@ pub(crate) mod test {
     impl QueryContext for UltraMinimal {
         type Def = Def;
         type Ref = !;
-        type Scope = ();
     }
 }
 
@@ -41,7 +39,5 @@ mod rustc {
     impl<'tcx> super::QueryContext for TyCtxt<'tcx> {
         type Def = layout::rustc::Def<'tcx>;
         type Ref = layout::rustc::Ref<'tcx>;
-
-        type Scope = Ty<'tcx>;
     }
 }

compiler/rustc_transmute/src/maybe_transmutable/query_context.rs

@@ -103,7 +103,6 @@ use crate::ascii::Char as AsciiChar;
 /// ```
 #[cfg_attr(not(test), rustc_diagnostic_item = "Default")]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[cfg_attr(not(bootstrap), rustc_trivial_field_reads)]
 pub trait Default: Sized {
     /// Returns the "default value" for a type.
     ///

library/core/src/default.rs

@@ -4,7 +4,7 @@
 
 trait Tr1: Copy { type As1: Copy; }
 trait Tr2: Copy { type As2: Copy; }
-trait Tr3: Copy { type As3: Copy; }
+trait Tr3: Copy { #[allow(dead_code)] type As3: Copy; }
 trait Tr4<'a>: Copy { type As4: Copy; }
 trait Tr5: Copy { type As5: Copy; }
 

tests/ui/associated-type-bounds/union-bounds.rs

@@ -11,6 +11,7 @@ impl Fiz for bool {}
 
 trait Grault {
     type A;
+    #[allow(dead_code)]
     type B;
 }
 

tests/ui/associated-types/impl-wf-cycle-5.fixed

@@ -11,6 +11,7 @@ impl Fiz for bool {}
 
 trait Grault {
     type A;
+    #[allow(dead_code)]
     type B;
 }
 

tests/ui/associated-types/impl-wf-cycle-5.rs

@@ -1,5 +1,5 @@
 error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
-  --> $DIR/impl-wf-cycle-5.rs:22:1
+  --> $DIR/impl-wf-cycle-5.rs:23:1
    |
 LL | / impl<T> Grault for (T,)
 LL | |
@@ -12,7 +12,7 @@ LL |       type A = ();
    |       ------ associated type `<(T,) as Grault>::A` is specified here
    |
 note: required for `(T,)` to implement `Grault`
-  --> $DIR/impl-wf-cycle-5.rs:22:9
+  --> $DIR/impl-wf-cycle-5.rs:23:9
    |
 LL | impl<T> Grault for (T,)
    |         ^^^^^^     ^^^^

tests/ui/associated-types/impl-wf-cycle-5.stderr

@@ -11,6 +11,7 @@ impl Fiz for bool {}
 
 trait Grault {
     type A;
+    #[allow(dead_code)]
     type B;
 }
 

tests/ui/associated-types/impl-wf-cycle-6.fixed

@@ -11,6 +11,7 @@ impl Fiz for bool {}
 
 trait Grault {
     type A;
+    #[allow(dead_code)]
     type B;
 }
 

tests/ui/associated-types/impl-wf-cycle-6.rs

@@ -1,5 +1,5 @@
 error[E0275]: overflow evaluating the requirement `<(T,) as Grault>::A == _`
-  --> $DIR/impl-wf-cycle-6.rs:22:1
+  --> $DIR/impl-wf-cycle-6.rs:23:1
    |
 LL | / impl<T: Grault> Grault for (T,)
 LL | |
@@ -11,7 +11,7 @@ LL |       type A = ();
    |       ------ associated type `<(T,) as Grault>::A` is specified here
    |
 note: required for `(T,)` to implement `Grault`
-  --> $DIR/impl-wf-cycle-6.rs:22:17
+  --> $DIR/impl-wf-cycle-6.rs:23:17
    |
 LL | impl<T: Grault> Grault for (T,)
    |                 ^^^^^^     ^^^^

tests/ui/associated-types/impl-wf-cycle-6.stderr

@@ -11,7 +11,7 @@ async fn foo() {
     async_in_foo(async_out_foo::<4>().await).await;
 }
 
-struct Faz<const N: usize>;
+struct Faz<const N: usize>; //~ WARN struct `Faz` is never constructed
 
 impl<const N: usize> Foo<N> for Faz<N> {}
 impl<const N: usize> Bar<N> for Faz<N> {

tests/ui/const-generics/cross_crate_complex.rs

@@ -0,0 +1,10 @@
+warning: struct `Faz` is never constructed
+  --> $DIR/cross_crate_complex.rs:14:8
+   |
+LL | struct Faz<const N: usize>;
+   |        ^^^
+   |
+   = note: `#[warn(dead_code)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/const-generics/cross_crate_complex.stderr

@@ -9,7 +9,7 @@ pub trait Foo {
         [(); Self::ASSOC_C]:;
 }
 
-struct Bar<const N: &'static ()>;
+struct Bar<const N: &'static ()>; //~ WARN struct `Bar` is never constructed
 impl<const N: &'static ()> Foo for Bar<N> {
     const ASSOC_C: usize = 3;
 

tests/ui/const-generics/issues/issue-86535-2.rs

@@ -0,0 +1,10 @@
+warning: struct `Bar` is never constructed
+  --> $DIR/issue-86535-2.rs:12:8
+   |
+LL | struct Bar<const N: &'static ()>;
+   |        ^^^
+   |
+   = note: `#[warn(dead_code)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/const-generics/issues/issue-86535-2.stderr

@@ -2,7 +2,7 @@
 #![feature(adt_const_params, unsized_const_params, generic_const_exprs)]
 #![allow(incomplete_features, unused_variables)]
 
-struct F<const S: &'static str>;
+struct F<const S: &'static str>; //~ WARN struct `F` is never constructed
 impl<const S: &'static str> X for F<{ S }> {
     const W: usize = 3;
 

tests/ui/const-generics/issues/issue-86535.rs

@@ -0,0 +1,10 @@
+warning: struct `F` is never constructed
+  --> $DIR/issue-86535.rs:5:8
+   |
+LL | struct F<const S: &'static str>;
+   |        ^
+   |
+   = note: `#[warn(dead_code)]` on by default
+
+warning: 1 warning emitted
+

tests/ui/const-generics/issues/issue-86535.stderr

@@ -6,7 +6,7 @@ macro_rules! define_vec {
     () => (
         mod foo {
             #[derive(PartialEq)]
-            pub struct bar;
+            pub struct bar; //~ WARN struct `bar` is never constructed
         }
     )
 }

tests/ui/deriving/deriving-in-macro.rs

@@ -0,0 +1,14 @@
+warning: struct `bar` is never constructed
+  --> $DIR/deriving-in-macro.rs:9:24
+   |
+LL |             pub struct bar;
+   |                        ^^^
+...
+LL | define_vec![];
+   | ------------- in this macro invocation
+   |
+   = note: `#[warn(dead_code)]` on by default
+   = note: this warning originates in the macro `define_vec` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: 1 warning emitted
+

tests/ui/deriving/deriving-in-macro.stderr

@@ -10,6 +10,7 @@ trait Collection<T> {
     type Iter<'iter>: Iterator<Item=&'iter T> where T: 'iter, Self: 'iter;
     type Family: CollectionFamily;
     // Test associated type defaults with parameters
+    #[allow(dead_code)]
     type Sibling<U>: Collection<U> =
         <<Self as Collection<T>>::Family as CollectionFamily>::Member<U>;
 

tests/ui/generic-associated-types/collections.rs

@@ -1,5 +1,7 @@
 //@ run-rustfix
 
+#![allow(dead_code)]
+
 use std::ops::Add;
 
 struct A<B>(B);

tests/ui/generic-associated-types/missing-bounds.fixed

@@ -1,5 +1,7 @@
 //@ run-rustfix
 
+#![allow(dead_code)]
+
 use std::ops::Add;
 
 struct A<B>(B);

tests/ui/generic-associated-types/missing-bounds.rs

@@ -1,5 +1,5 @@
 error: equality constraints are not yet supported in `where` clauses
-  --> $DIR/missing-bounds.rs:37:33
+  --> $DIR/missing-bounds.rs:39:33
    |
 LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
    |                                 ^^^^^^^^^^^^^^^^^^^^^^ not supported
@@ -11,7 +11,7 @@ LL | impl<B: Add> Add for E<B> where B: Add<Output = B> {
    |                                 ~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:11:11
+  --> $DIR/missing-bounds.rs:13:11
    |
 LL | impl<B> Add for A<B> where B: Add {
    |      - expected this type parameter
@@ -24,14 +24,14 @@ LL |         A(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 help: the type constructed contains `<B as Add>::Output` due to the type of the argument passed
-  --> $DIR/missing-bounds.rs:11:9
+  --> $DIR/missing-bounds.rs:13:9
    |
 LL |         A(self.0 + rhs.0)
    |         ^^--------------^
    |           |
    |           this argument influences the type of `A`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:5:8
+  --> $DIR/missing-bounds.rs:7:8
    |
 LL | struct A<B>(B);
    |        ^
@@ -41,7 +41,7 @@ LL | impl<B> Add for A<B> where B: Add<Output = B> {
    |                                  ++++++++++++
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:21:14
+  --> $DIR/missing-bounds.rs:23:14
    |
 LL | impl<B: Add> Add for C<B> {
    |      - expected this type parameter
@@ -54,7 +54,7 @@ LL |         Self(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:15:8
+  --> $DIR/missing-bounds.rs:17:8
    |
 LL | struct C<B>(B);
    |        ^
@@ -64,7 +64,7 @@ LL | impl<B: Add<Output = B>> Add for C<B> {
    |            ++++++++++++
 
 error[E0369]: cannot add `B` to `B`
-  --> $DIR/missing-bounds.rs:31:21
+  --> $DIR/missing-bounds.rs:33:21
    |
 LL |         Self(self.0 + rhs.0)
    |              ------ ^ ----- B
@@ -77,7 +77,7 @@ LL | impl<B: std::ops::Add<Output = B>> Add for D<B> {
    |       +++++++++++++++++++++++++++
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:42:14
+  --> $DIR/missing-bounds.rs:44:14
    |
 LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
    |      - expected this type parameter
@@ -90,7 +90,7 @@ LL |         Self(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:35:8
+  --> $DIR/missing-bounds.rs:37:8
    |
 LL | struct E<B>(B);
    |        ^

tests/ui/generic-associated-types/missing-bounds.stderr

@@ -1,5 +1,7 @@
 //@ run-rustfix
 
+#![allow(dead_code)]
+
 struct S<T>(T);
 struct S2;
 

tests/ui/impl-trait/extra-impl-in-trait-impl.fixed

@@ -1,5 +1,7 @@
 //@ run-rustfix
 
+#![allow(dead_code)]
+
 struct S<T>(T);
 struct S2;
 

tests/ui/impl-trait/extra-impl-in-trait-impl.rs

@@ -1,23 +1,23 @@
 error: unexpected `impl` keyword
-  --> $DIR/extra-impl-in-trait-impl.rs:6:18
+  --> $DIR/extra-impl-in-trait-impl.rs:8:18
    |
 LL | impl<T: Default> impl Default for S<T> {
    |                  ^^^^^ help: remove the extra `impl`
    |
 note: this is parsed as an `impl Trait` type, but a trait is expected at this position
-  --> $DIR/extra-impl-in-trait-impl.rs:6:18
+  --> $DIR/extra-impl-in-trait-impl.rs:8:18
    |
 LL | impl<T: Default> impl Default for S<T> {
    |                  ^^^^^^^^^^^^
 
 error: unexpected `impl` keyword
-  --> $DIR/extra-impl-in-trait-impl.rs:12:6
+  --> $DIR/extra-impl-in-trait-impl.rs:14:6
    |
 LL | impl impl Default for S2 {
    |      ^^^^^ help: remove the extra `impl`
    |
 note: this is parsed as an `impl Trait` type, but a trait is expected at this position
-  --> $DIR/extra-impl-in-trait-impl.rs:12:6
+  --> $DIR/extra-impl-in-trait-impl.rs:14:6
    |
 LL | impl impl Default for S2 {
    |      ^^^^^^^^^^^^

tests/ui/impl-trait/extra-impl-in-trait-impl.stderr

@@ -0,0 +1,19 @@
+//@ check-pass
+
+#![deny(dead_code)]
+
+struct T<X>(X);
+
+type A<X> = T<X>;
+
+trait Tr {
+    fn foo();
+}
+
+impl<X> Tr for T<A<X>> {
+    fn foo() {}
+}
+
+fn main() {
+   T::<T<()>>::foo();
+}

tests/ui/lint/dead-code/alias-type-used-as-generic-arg-in-impl.rs

@@ -4,8 +4,8 @@
 
 #![deny(dead_code)]
 
+#[allow(dead_code)]
 struct Foo {
-    #[allow(dead_code)]
     inner: u32,
 }