Trying out a new message that works a little better for values *and* items

Author: sunjay

compiler/rustc_passes/src/dead.rs

@@ -600,10 +600,11 @@ impl DeadVisitor<'tcx> {
                     Applicability::MachineApplicable,
                 )
                 .note(&format!(
-                    "the leading underscore helps signal to the reader that the {} may still serve\n\
-                    a purpose even if it isn't used in a way that we can detect (e.g. the {}\nis \
-                    only used through FFI or used only for its effect when dropped)",
-                    descr, descr,
+                    "The leading underscore signals to the reader that while the {} may not be {}\n\
+                    by any Rust code, it still serves some other purpose that isn't detected by rustc.\n\
+                    (e.g. some values are used for their effect when dropped or used in FFI code\n\
+                    exclusively through raw pointers)",
+                    descr, participle,
                 ));
                 // Force the note we added to the front, before any other subdiagnostics
                 diag.children.rotate_right(1);

src/test/ui/associated-consts/associated-const-dead-code.stderr

@@ -4,9 +4,10 @@ error: associated constant is never used: `BAR`
 LL |     const BAR: u32 = 1;
    |     ^^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_BAR`
    |
-   = note: the leading underscore helps signal to the reader that the associated constant may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the associated constant
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the associated constant may not be used
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/associated-const-dead-code.rs:1:9
    |

src/test/ui/derive-uninhabited-enum-38885.stderr

@@ -4,9 +4,10 @@ warning: variant is never constructed: `Void`
 LL |     Void(Void),
    |     ^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_Void`
    |
-   = note: the leading underscore helps signal to the reader that the variant may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the variant
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the variant may not be constructed
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
    = note: `-W dead-code` implied by `-W unused`
 
 warning: 1 warning emitted

src/test/ui/issues/issue-37515.stderr

@@ -4,9 +4,10 @@ warning: type alias is never used: `Z`
 LL | type Z = dyn for<'x> Send;
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_Z`
    |
-   = note: the leading underscore helps signal to the reader that the type alias may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the type alias
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the type alias may not be used
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/issue-37515.rs:3:9
    |

src/test/ui/lint/dead-code/basic.stderr

@@ -4,9 +4,10 @@ error: function is never used: `foo`
 LL | fn foo() {
    |    ^^^ help: if this is intentional, prefix it with an underscore: `_foo`
    |
-   = note: the leading underscore helps signal to the reader that the function may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the function
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the function may not be used
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/basic.rs:1:9
    |

src/test/ui/lint/dead-code/const-and-self.stderr

@@ -4,9 +4,10 @@ warning: variant is never constructed: `B`
 LL |     B,
    |     ^ help: if this is intentional, prefix it with an underscore: `_B`
    |
-   = note: the leading underscore helps signal to the reader that the variant may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the variant
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the variant may not be constructed
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/const-and-self.rs:3:9
    |
@@ -19,9 +20,10 @@ warning: variant is never constructed: `C`
 LL |     C,
    |     ^ help: if this is intentional, prefix it with an underscore: `_C`
    |
-   = note: the leading underscore helps signal to the reader that the variant may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the variant
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the variant may not be constructed
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 
 warning: 2 warnings emitted
 

src/test/ui/lint/dead-code/drop-only-field-issue-81658.stderr

@@ -4,9 +4,10 @@ error: field is never read: `guard`
 LL |     guard: MutexGuard<'a, T>,
    |     ^^^^^^^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_guard`
    |
-   = note: the leading underscore helps signal to the reader that the field may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the field
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the field may not be read
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/drop-only-field-issue-81658.rs:8:9
    |

src/test/ui/lint/dead-code/empty-unused-enum.stderr

@@ -4,9 +4,10 @@ error: enum is never used: `E`
 LL | enum E {}
    |      ^ help: if this is intentional, prefix it with an underscore: `_E`
    |
-   = note: the leading underscore helps signal to the reader that the enum may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the enum
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the enum may not be used
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/empty-unused-enum.rs:1:9
    |

src/test/ui/lint/dead-code/field-used-in-ffi-issue-81658.stderr

@@ -4,9 +4,10 @@ error: field is never read: `items`
 LL |     items: Option<Vec<T>>,
    |     ^^^^^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_items`
    |
-   = note: the leading underscore helps signal to the reader that the field may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the field
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the field may not be read
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/field-used-in-ffi-issue-81658.rs:7:9
    |

src/test/ui/lint/dead-code/impl-trait.stderr

@@ -4,9 +4,10 @@ error: type alias is never used: `Unused`
 LL | type Unused = ();
    | ^^^^^^^^^^^^^^^^^ help: if this is intentional, prefix it with an underscore: `_Unused`
    |
-   = note: the leading underscore helps signal to the reader that the type alias may still serve
-           a purpose even if it isn't used in a way that we can detect (e.g. the type alias
-           is only used through FFI or used only for its effect when dropped)
+   = note: The leading underscore signals to the reader that while the type alias may not be used
+           by any Rust code, it still serves some other purpose that isn't detected by rustc.
+           (e.g. some values are used for their effect when dropped or used in FFI code
+           exclusively through raw pointers)
 note: the lint level is defined here
   --> $DIR/impl-trait.rs:1:9
    |