Auto merge of #48309 - mark-i-m:anon_param_lint, r=nikomatsakis

Make anon params lint warn-by-default

This is intended as a followup on anonymous parameters deprecation.

Cross-posting from #41686:

> After having read a bit more of the discussion that I can find, I propose a more aggressive deprecation strategy:
> - We make the lint warn-by-default as soon as possible
> - We make anon parameters a hard error at the epoch boundary

cc @matklad @est31 @aturon

src/librustc/lib.rs

@@ -69,6 +69,7 @@
 #![feature(catch_expr)]
 #![feature(test)]
 #![feature(in_band_lifetimes)]
+#![feature(macro_at_most_once_rep)]
 
 #![recursion_limit="512"]
 

src/librustc/lint/mod.rs

@@ -77,8 +77,9 @@ pub struct Lint {
     /// e.g. "imports that are never used"
     pub desc: &'static str,
 
-    /// Deny lint after this edition
-    pub edition_deny: Option<Edition>,
+    /// Starting at the given edition, default to the given lint level. If this is `None`, then use
+    /// `default_level`.
+    pub edition_lint_opts: Option<(Edition, Level)>,
 }
 
 impl Lint {
@@ -88,32 +89,32 @@ impl Lint {
     }
 
     pub fn default_level(&self, session: &Session) -> Level {
-        if let Some(edition_deny) = self.edition_deny {
-            if session.edition() >= edition_deny {
-                return Level::Deny
-            }
-        }
-        self.default_level
+        self.edition_lint_opts
+            .filter(|(e, _)| *e <= session.edition())
+            .map(|(_, l)| l)
+            .unwrap_or(self.default_level)
     }
 }
 
 /// Declare a static item of type `&'static Lint`.
 #[macro_export]
 macro_rules! declare_lint {
-    ($vis: vis $NAME: ident, $Level: ident, $desc: expr, $edition: expr) => (
-        $vis static $NAME: &$crate::lint::Lint = &$crate::lint::Lint {
-            name: stringify!($NAME),
-            default_level: $crate::lint::$Level,
-            desc: $desc,
-            edition_deny: Some($edition)
-        };
-    );
     ($vis: vis $NAME: ident, $Level: ident, $desc: expr) => (
         $vis static $NAME: &$crate::lint::Lint = &$crate::lint::Lint {
             name: stringify!($NAME),
             default_level: $crate::lint::$Level,
             desc: $desc,
-            edition_deny: None,
+            edition_lint_opts: None,
+        };
+    );
+    ($vis: vis $NAME: ident, $Level: ident, $desc: expr,
+     $lint_edition: expr => $edition_level: ident $(,)?
+    ) => (
+        $vis static $NAME: &$crate::lint::Lint = &$crate::lint::Lint {
+            name: stringify!($NAME),
+            default_level: $crate::lint::$Level,
+            desc: $desc,
+            edition_lint_opts: Some(($lint_edition, $crate::lint::Level::$edition_level)),
         };
     );
 }
@@ -121,8 +122,7 @@ macro_rules! declare_lint {
 /// Declare a static `LintArray` and return it as an expression.
 #[macro_export]
 macro_rules! lint_array {
-    ($( $lint:expr ),*,) => { lint_array!( $( $lint ),* ) };
-    ($( $lint:expr ),*) => {{
+    ($( $lint:expr ),* $(,)?) => {{
          static ARRAY: LintArray = &[ $( &$lint ),* ];
          ARRAY
     }}

src/librustc_lint/builtin.rs

@@ -43,6 +43,7 @@ use std::collections::HashSet;
 
 use syntax::ast;
 use syntax::attr;
+use syntax::edition::Edition;
 use syntax::feature_gate::{AttributeGate, AttributeType, Stability, deprecated_attributes};
 use syntax_pos::{BytePos, Span, SyntaxContext};
 use syntax::symbol::keywords;
@@ -616,7 +617,8 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for MissingDebugImplementations {
 declare_lint! {
     pub ANONYMOUS_PARAMETERS,
     Allow,
-    "detects anonymous parameters"
+    "detects anonymous parameters",
+    Edition::Edition2018 => Warn,
 }
 
 /// Checks for use of anonymous parameters (RFC 1685)
@@ -637,9 +639,29 @@ impl EarlyLintPass for AnonymousParameters {
                     match arg.pat.node {
                         ast::PatKind::Ident(_, ident, None) => {
                             if ident.name == keywords::Invalid.name() {
-                                cx.span_lint(ANONYMOUS_PARAMETERS,
-                                             arg.pat.span,
-                                             "use of deprecated anonymous parameter");
+                                let ty_snip = cx
+                                    .sess
+                                    .codemap()
+                                    .span_to_snippet(arg.ty.span);
+
+                                let (ty_snip, appl) = if let Ok(snip) = ty_snip {
+                                    (snip, Applicability::MachineApplicable)
+                                } else {
+                                    ("<type>".to_owned(), Applicability::HasPlaceholders)
+                                };
+
+                                cx.struct_span_lint(
+                                    ANONYMOUS_PARAMETERS,
+                                    arg.pat.span,
+                                    "anonymous parameters are deprecated and will be \
+                                     removed in the next edition."
+                                ).span_suggestion_with_applicability(
+                                    arg.pat.span,
+                                    "Try naming the parameter or explicitly \
+                                    ignoring it",
+                                    format!("_: {}", ty_snip),
+                                    appl
+                                ).emit();
                             }
                         }
                         _ => (),

src/librustc_lint/lib.rs

@@ -29,6 +29,7 @@
 #![feature(macro_vis_matcher)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(macro_at_most_once_rep)]
 
 extern crate syntax;
 #[macro_use]

src/test/compile-fail-fulldeps/auxiliary/lint_for_crate.rs

@@ -13,6 +13,7 @@
 #![feature(plugin_registrar, rustc_private)]
 #![feature(box_syntax)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 
 #[macro_use] extern crate rustc;
 extern crate rustc_plugin;

src/test/compile-fail-fulldeps/auxiliary/lint_group_plugin_test.rs

@@ -13,6 +13,7 @@
 #![feature(plugin_registrar)]
 #![feature(box_syntax, rustc_private)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 
 // Load rustc as a plugin to get macros
 #[macro_use]

src/test/compile-fail-fulldeps/auxiliary/lint_plugin_test.rs

@@ -13,6 +13,7 @@
 #![feature(plugin_registrar)]
 #![feature(box_syntax, rustc_private)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 
 extern crate syntax;
 

src/test/compile-fail/anon-params-deprecated.rs

@@ -12,13 +12,13 @@
 // Test for the anonymous_parameters deprecation lint (RFC 1685)
 
 trait T {
-    fn foo(i32); //~ ERROR use of deprecated anonymous parameter
+    fn foo(i32); //~ ERROR anonymous parameters are deprecated
                  //~| WARNING hard error
 
     fn bar_with_default_impl(String, String) {}
-    //~^ ERROR use of deprecated anonymous parameter
+    //~^ ERROR anonymous parameters are deprecated
     //~| WARNING hard error
-    //~| ERROR use of deprecated anonymous parameter
+    //~| ERROR anonymous parameters are deprecated
     //~| WARNING hard error
 }
 

src/test/compile-fail/future-incompatible-lint-group.rs

@@ -11,7 +11,7 @@
 #![deny(future_incompatible)]
 
 trait Tr {
-    fn f(u8) {} //~ ERROR use of deprecated anonymous parameter
+    fn f(u8) {} //~ ERROR anonymous parameters are deprecated
                 //~^ WARN this was previously accepted
 }
 

src/test/run-pass-fulldeps/auxiliary/lint_for_crate.rs

@@ -13,6 +13,7 @@
 #![feature(plugin_registrar, rustc_private)]
 #![feature(box_syntax)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 
 #[macro_use] extern crate rustc;
 extern crate rustc_plugin;

src/test/run-pass-fulldeps/proc-macro/auxiliary/issue-40001-plugin.rs

@@ -9,6 +9,7 @@
 // except according to those terms.
 #![feature(box_syntax, plugin, plugin_registrar, rustc_private)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 #![crate_type = "dylib"]
 
 #[macro_use]

src/test/ui-fulldeps/auxiliary/lint_group_plugin_test.rs

@@ -13,6 +13,7 @@
 #![feature(plugin_registrar)]
 #![feature(box_syntax, rustc_private)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 
 // Load rustc as a plugin to get macros
 #[macro_use]

src/test/ui-fulldeps/auxiliary/lint_plugin_test.rs

@@ -13,6 +13,7 @@
 #![feature(plugin_registrar)]
 #![feature(box_syntax, rustc_private)]
 #![feature(macro_vis_matcher)]
+#![feature(macro_at_most_once_rep)]
 
 extern crate syntax;
 

src/test/ui/lint-anon-param-edition.fixed

@@ -0,0 +1,23 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// tests that the anonymous_parameters lint is warn-by-default on the 2018 edition
+
+// compile-pass
+// compile-flags: --edition=2018
+// run-rustfix
+
+trait Foo {
+    fn foo(_: u8);
+    //^ WARN anonymous parameters are deprecated
+    //| WARN this was previously accepted
+}
+
+fn main() {}

src/test/ui/lint-anon-param-edition.rs

@@ -0,0 +1,23 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// tests that the anonymous_parameters lint is warn-by-default on the 2018 edition
+
+// compile-pass
+// compile-flags: --edition=2018
+// run-rustfix
+
+trait Foo {
+    fn foo(u8);
+    //^ WARN anonymous parameters are deprecated
+    //| WARN this was previously accepted
+}
+
+fn main() {}

src/test/ui/lint-anon-param-edition.stderr

@@ -0,0 +1,10 @@
+warning: anonymous parameters are deprecated and will be removed in the next edition.
+  --> $DIR/lint-anon-param-edition.rs:18:12
+   |
+LL |     fn foo(u8);
+   |            ^^ help: Try naming the parameter or explicitly ignoring it: `_: u8`
+   |
+   = note: #[warn(anonymous_parameters)] on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #41686 <https://github.com/rust-lang/rust/issues/41686>
+