dead-code lint: say "constructed", "called" for structs, functions

Respectively.

This is a sequel to November 2017's rust-lang#46103 / 1a9dc2e. It had been
reported (more than once—at least rust-lang#19140, rust-lang#44083, and rust-lang#44565) that the
"never used" language was confusing for enum variants that were "used"
as match patterns, so the wording was changed to say never "constructed"
specifically for enum variants. More recently, the same issue was raised
for structs (rust-lang#52325). It seems consistent to say "constructed" here,
too, for the same reasons.

While we're here, we can also use more specific word "called" for unused
functions and methods. (We declined to do this in rust-lang#46103, but the
rationale given in the commit message doesn't actually make sense.)

This resolves rust-lang#52325.

Author: zackmdavis

src/librustc/middle/dead.rs

@@ -567,12 +567,17 @@ impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
                 hir::ItemImpl(..) => self.tcx.sess.codemap().def_span(item.span),
                 _ => item.span,
             };
+            let participle = match item.node {
+                hir::ItemFn(..) => "called",
+                hir::ItemStruct(..) => "constructed",
+                _ => "used"
+            };
             self.warn_dead_code(
                 item.id,
                 span,
                 item.name,
                 item.node.descriptive_variant(),
-                "used",
+                participle,
             );
         } else {
             // Only continue if we didn't warn
@@ -622,7 +627,8 @@ impl<'a, 'tcx> Visitor<'tcx> for DeadVisitor<'a, 'tcx> {
             hir::ImplItemKind::Method(_, body_id) => {
                 if !self.symbol_is_live(impl_item.id, None) {
                     let span = self.tcx.sess.codemap().def_span(impl_item.span);
-                    self.warn_dead_code(impl_item.id, span, impl_item.ident.name, "method", "used");
+                    self.warn_dead_code(impl_item.id, span, impl_item.ident.name,
+                                        "method", "called");
                 }
                 self.visit_nested_body(body_id)
             }

src/test/compile-fail/fail-no-dead-code-core.rs

@@ -14,7 +14,7 @@
 #[macro_use]
 extern crate core;
 
-fn foo() { //~ ERROR function is never used
+fn foo() { //~ ERROR function is never called
 
     // none of these should have any dead_code exposed to the user
     panic!();

src/test/compile-fail/fail-no-dead-code.rs

@@ -11,7 +11,7 @@
 #![deny(dead_code)]
 #![allow(unreachable_code)]
 
-fn foo() { //~ ERROR function is never used
+fn foo() { //~ ERROR function is never called
 
     // none of these should have any dead_code exposed to the user
     panic!();

src/test/compile-fail/lint-dead-code-1.rs

@@ -19,7 +19,7 @@
 pub use foo2::Bar2;
 
 mod foo {
-    pub struct Bar; //~ ERROR: struct is never used
+    pub struct Bar; //~ ERROR: struct is never constructed
 }
 
 mod foo2 {
@@ -42,7 +42,7 @@ const CONST_USED_IN_ENUM_DISCRIMINANT: isize = 11;
 
 pub type typ = *const UsedStruct4;
 pub struct PubStruct;
-struct PrivStruct; //~ ERROR: struct is never used
+struct PrivStruct; //~ ERROR: struct is never constructed
 struct UsedStruct1 {
     #[allow(dead_code)]
     x: isize
@@ -95,17 +95,17 @@ pub fn pub_fn() {
     }
     f::<StructUsedInGeneric>();
 }
-fn priv_fn() { //~ ERROR: function is never used
+fn priv_fn() { //~ ERROR: function is never called
     let unused_struct = PrivStruct;
 }
 fn used_fn() {}
 
-fn foo() { //~ ERROR: function is never used
+fn foo() { //~ ERROR: function is never called
     bar();
     let unused_enum = priv_enum::foo2;
 }
 
-fn bar() { //~ ERROR: function is never used
+fn bar() { //~ ERROR: function is never called
     foo();
 }
 

src/test/compile-fail/lint-dead-code-2.rs

@@ -29,10 +29,10 @@ impl Bar for Foo {
 
 fn live_fn() {}
 
-fn dead_fn() {} //~ ERROR: function is never used
+fn dead_fn() {} //~ ERROR: function is never called
 
 #[main]
-fn dead_fn2() {} //~ ERROR: function is never used
+fn dead_fn2() {} //~ ERROR: function is never called
 
 fn used_fn() {}
 
@@ -45,7 +45,7 @@ fn start(_: isize, _: *const *const u8) -> isize {
 }
 
 // this is not main
-fn main() { //~ ERROR: function is never used
+fn main() { //~ ERROR: function is never called
     dead_fn();
     dead_fn2();
 }

src/test/compile-fail/lint-dead-code-3.rs

@@ -20,14 +20,14 @@ extern {
     pub fn extern_foo();
 }
 
-struct Foo; //~ ERROR: struct is never used
+struct Foo; //~ ERROR: struct is never constructed
 impl Foo {
-    fn foo(&self) { //~ ERROR: method is never used
+    fn foo(&self) { //~ ERROR: method is never called
         bar()
     }
 }
 
-fn bar() { //~ ERROR: function is never used
+fn bar() { //~ ERROR: function is never called
     fn baz() {}
 
     Foo.foo();

src/test/compile-fail/test-warns-dead-code.rs

@@ -12,6 +12,6 @@
 
 #![deny(dead_code)]
 
-fn dead() {} //~ error: function is never used: `dead`
+fn dead() {} //~ error: function is never called: `dead`
 
 fn main() {}

src/test/ui-fulldeps/lint-plugin-cmdline-allow.stderr

@@ -1,4 +1,4 @@
-warning: function is never used: `lintme`
+warning: function is never called: `lintme`
   --> $DIR/lint-plugin-cmdline-allow.rs:20:1
    |
 LL | fn lintme() { }

src/test/ui/path-lookahead.rs

@@ -14,11 +14,11 @@
 
 // Parser test for #37765
 
-fn with_parens<T: ToString>(arg: T) -> String { //~WARN function is never used: `with_parens`
+fn with_parens<T: ToString>(arg: T) -> String { //~WARN function is never called: `with_parens`
   return (<T as ToString>::to_string(&arg)); //~WARN unnecessary parentheses around `return` value
 }
 
-fn no_parens<T: ToString>(arg: T) -> String { //~WARN function is never used: `no_parens`
+fn no_parens<T: ToString>(arg: T) -> String { //~WARN function is never called: `no_parens`
   return <T as ToString>::to_string(&arg);
 }
 

src/test/ui/path-lookahead.stderr

@@ -11,10 +11,10 @@ LL | #![warn(unused)]
    |         ^^^^^^
    = note: #[warn(unused_parens)] implied by #[warn(unused)]
 
-warning: function is never used: `with_parens`
+warning: function is never called: `with_parens`
   --> $DIR/path-lookahead.rs:17:1
    |
-LL | fn with_parens<T: ToString>(arg: T) -> String { //~WARN function is never used: `with_parens`
+LL | fn with_parens<T: ToString>(arg: T) -> String { //~WARN function is never called: `with_parens`
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
 note: lint level defined here
@@ -24,9 +24,9 @@ LL | #![warn(unused)]
    |         ^^^^^^
    = note: #[warn(dead_code)] implied by #[warn(unused)]
 
-warning: function is never used: `no_parens`
+warning: function is never called: `no_parens`
   --> $DIR/path-lookahead.rs:21:1
    |
-LL | fn no_parens<T: ToString>(arg: T) -> String { //~WARN function is never used: `no_parens`
+LL | fn no_parens<T: ToString>(arg: T) -> String { //~WARN function is never called: `no_parens`
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^