Turn non_fmt_panic into a future_incompatible edition lint.

compiler/rustc_lint/src/non_fmt_panic.rs

@@ -4,6 +4,8 @@ use rustc_errors::{pluralize, Applicability};
 use rustc_hir as hir;
 use rustc_middle::ty;
 use rustc_parse_format::{ParseMode, Parser, Piece};
+use rustc_session::lint::FutureIncompatibilityReason;
+use rustc_span::edition::Edition;
 use rustc_span::{hygiene, sym, symbol::kw, symbol::SymbolStr, InnerSpan, Span, Symbol};
 
 declare_lint! {
@@ -30,6 +32,10 @@ declare_lint! {
     NON_FMT_PANIC,
     Warn,
     "detect single-argument panic!() invocations in which the argument is not a format string",
+    @future_incompatible = FutureIncompatibleInfo {
+        reason: FutureIncompatibilityReason::EditionSemanticsChange(Edition::Edition2021),
+        explain_reason: false,
+    };
     report_in_external_macro
 }
 
@@ -87,7 +93,8 @@ fn check_panic<'tcx>(cx: &LateContext<'tcx>, f: &'tcx hir::Expr<'tcx>, arg: &'tc
 
     cx.struct_span_lint(NON_FMT_PANIC, arg_span, |lint| {
         let mut l = lint.build("panic message is not a string literal");
-        l.note("this is no longer accepted in Rust 2021");
+        l.note("this usage of panic!() is deprecated; it will be a hard error in Rust 2021");
+        l.note("for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>");
         if !span.contains(arg_span) {
             // No clue where this argument is coming from.
             l.emit();

compiler/rustc_lint_defs/src/lib.rs

@@ -145,6 +145,11 @@ pub struct FutureIncompatibleInfo {
     /// The reason for the lint used by diagnostics to provide
     /// the right help message
     pub reason: FutureIncompatibilityReason,
+    /// Whether to explain the reason to the user.
+    ///
+    /// Set to false for lints that already include a more detailed
+    /// explanation.
+    pub explain_reason: bool,
     /// Information about a future breakage, which will
     /// be emitted in JSON messages to be displayed by Cargo
     /// for upstream deps
@@ -185,6 +190,7 @@ impl FutureIncompatibleInfo {
         FutureIncompatibleInfo {
             reference: "",
             reason: FutureIncompatibilityReason::FutureReleaseError,
+            explain_reason: true,
             future_breakage: None,
         }
     }

compiler/rustc_middle/src/lint.rs

@@ -398,9 +398,14 @@ pub fn struct_lint_level<'s, 'd>(
                  it will become a hard error in a future release!"
                     .to_owned()
             };
-            let citation = format!("for more information, see {}", future_incompatible.reference);
-            err.warn(&explanation);
-            err.note(&citation);
+            if future_incompatible.explain_reason {
+                err.warn(&explanation);
+            }
+            if !future_incompatible.reference.is_empty() {
+                let citation =
+                    format!("for more information, see {}", future_incompatible.reference);
+                err.note(&citation);
+            }
         }
 
         // Finally, run `decorate`. This function is also responsible for emitting the diagnostic.

src/test/ui/non-fmt-panic.stderr

@@ -61,7 +61,8 @@ warning: panic message is not a string literal
 LL |     assert!(false, S);
    |                    ^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     assert!(false, "{}", S);
@@ -85,7 +86,8 @@ warning: panic message is not a string literal
 LL |     panic!(C);
    |            ^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     panic!("{}", C);
@@ -101,7 +103,8 @@ warning: panic message is not a string literal
 LL |     panic!(S);
    |            ^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     panic!("{}", S);
@@ -117,7 +120,8 @@ warning: panic message is not a string literal
 LL |     std::panic!(123);
    |                 ^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     std::panic!("{}", 123);
@@ -133,7 +137,8 @@ warning: panic message is not a string literal
 LL |     core::panic!(&*"abc");
    |                  ^^^^^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     core::panic!("{}", &*"abc");
@@ -181,15 +186,17 @@ warning: panic message is not a string literal
 LL |     fancy_panic::fancy_panic!(S);
    |                               ^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 
 warning: panic message is not a string literal
   --> $DIR/non-fmt-panic.rs:36:12
    |
 LL |     panic!(a!());
    |            ^^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     panic!("{}", a!());
@@ -205,7 +212,8 @@ warning: panic message is not a string literal
 LL |     panic!(format!("{}", 1));
    |            ^^^^^^^^^^^^^^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
    = note: the panic!() macro supports formatting, so there's no need for the format!() macro here
 help: remove the `format!(..)` macro call
    |
@@ -218,7 +226,8 @@ warning: panic message is not a string literal
 LL |     assert!(false, format!("{}", 1));
    |                    ^^^^^^^^^^^^^^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
    = note: the assert!() macro supports formatting, so there's no need for the format!() macro here
 help: remove the `format!(..)` macro call
    |
@@ -231,7 +240,8 @@ warning: panic message is not a string literal
 LL |     debug_assert!(false, format!("{}", 1));
    |                          ^^^^^^^^^^^^^^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
    = note: the debug_assert!() macro supports formatting, so there's no need for the format!() macro here
 help: remove the `format!(..)` macro call
    |
@@ -244,7 +254,8 @@ warning: panic message is not a string literal
 LL |     panic![123];
    |            ^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     panic!["{}", 123];
@@ -260,7 +271,8 @@ warning: panic message is not a string literal
 LL |     panic!{123};
    |            ^^^
    |
-   = note: this is no longer accepted in Rust 2021
+   = note: this usage of panic!() is deprecated; it will be a hard error in Rust 2021
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/panic-macro-consistency.html>
 help: add a "{}" format string to Display the message
    |
 LL |     panic!{"{}", 123};