Rollup merge of rust-lang#87385 - Aaron1011:final-enable-semi, r=petrochenkov

Make `SEMICOLON_IN_EXPRESSIONS_FROM_MACROS` warn by default

This PR makes the `SEMICOLON_IN_EXPRESSIONS_FROM_MACROS` lint warn by default.

To avoid showing a large number of un-actionable warnings to users, we only enable the lint for macros defined in the same crate. This ensures that users will be able to fix the warning by simply removing a semicolon.

In the future, I'd like to enable this lint unconditionally, and eventually make it into a hard error in a future edition. This PR is a step towards that goal.

Author: JohnTitor

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -45,6 +45,8 @@ crate struct ParserAnyMacro<'a> {
     lint_node_id: NodeId,
     is_trailing_mac: bool,
     arm_span: Span,
+    /// Whether or not this macro is defined in the current crate
+    is_local: bool,
 }
 
 crate fn annotate_err_with_kind(
@@ -124,6 +126,7 @@ impl<'a> ParserAnyMacro<'a> {
             lint_node_id,
             arm_span,
             is_trailing_mac,
+            is_local,
         } = *self;
         let snapshot = &mut parser.clone();
         let fragment = match parse_ast_fragment(parser, kind) {
@@ -138,13 +141,15 @@ impl<'a> ParserAnyMacro<'a> {
         // `macro_rules! m { () => { panic!(); } }` isn't parsed by `.parse_expr()`,
         // but `m!()` is allowed in expression positions (cf. issue #34706).
         if kind == AstFragmentKind::Expr && parser.token == token::Semi {
-            parser.sess.buffer_lint_with_diagnostic(
-                SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
-                parser.token.span,
-                lint_node_id,
-                "trailing semicolon in macro used in expression position",
-                BuiltinLintDiagnostics::TrailingMacro(is_trailing_mac, macro_ident),
-            );
+            if is_local {
+                parser.sess.buffer_lint_with_diagnostic(
+                    SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
+                    parser.token.span,
+                    lint_node_id,
+                    "trailing semicolon in macro used in expression position",
+                    BuiltinLintDiagnostics::TrailingMacro(is_trailing_mac, macro_ident),
+                );
+            }
             parser.bump();
         }
 
@@ -162,6 +167,7 @@ struct MacroRulesMacroExpander {
     lhses: Vec<mbe::TokenTree>,
     rhses: Vec<mbe::TokenTree>,
     valid: bool,
+    is_local: bool,
 }
 
 impl TTMacroExpander for MacroRulesMacroExpander {
@@ -183,6 +189,7 @@ impl TTMacroExpander for MacroRulesMacroExpander {
             input,
             &self.lhses,
             &self.rhses,
+            self.is_local,
         )
     }
 }
@@ -210,6 +217,7 @@ fn generic_extension<'cx>(
     arg: TokenStream,
     lhses: &[mbe::TokenTree],
     rhses: &[mbe::TokenTree],
+    is_local: bool,
 ) -> Box<dyn MacResult + 'cx> {
     let sess = &cx.sess.parse_sess;
 
@@ -311,6 +319,7 @@ fn generic_extension<'cx>(
                     lint_node_id: cx.current_expansion.lint_node_id,
                     is_trailing_mac: cx.current_expansion.is_trailing_mac,
                     arm_span,
+                    is_local,
                 });
             }
             Failure(token, msg) => match best_failure {
@@ -544,6 +553,9 @@ pub fn compile_declarative_macro(
         lhses,
         rhses,
         valid,
+        // Macros defined in the current crate have a real node id,
+        // whereas macros from an external crate have a dummy id.
+        is_local: def.id != DUMMY_NODE_ID,
     }))
 }
 

compiler/rustc_lint_defs/src/builtin.rs

@@ -2799,7 +2799,7 @@ declare_lint! {
     /// [issue #79813]: https://github.com/rust-lang/rust/issues/79813
     /// [future-incompatible]: ../index.md#future-incompatible-lints
     pub SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,
-    Allow,
+    Warn,
     "trailing semicolon in macro body used as expression",
     @future_incompatible = FutureIncompatibleInfo {
         reference: "issue #79813 <https://github.com/rust-lang/rust/issues/79813>",

library/std/src/macros.rs

@@ -290,7 +290,7 @@ macro_rules! dbg {
     // `$val` expression could be a block (`{ .. }`), in which case the `eprintln!`
     // will be malformed.
     () => {
-        $crate::eprintln!("[{}:{}]", $crate::file!(), $crate::line!());
+        $crate::eprintln!("[{}:{}]", $crate::file!(), $crate::line!())
     };
     ($val:expr $(,)?) => {
         // Use of `match` here is intentional because it affects the lifetimes

src/test/ui/hygiene/auxiliary/intercrate.rs

@@ -5,7 +5,7 @@ pub mod foo {
     mod bar {
         fn f() -> u32 { 1 }
         pub macro m() {
-            f();
+            f()
         }
     }
 }

src/test/ui/hygiene/hygienic-label-1.rs

@@ -3,5 +3,5 @@ macro_rules! foo {
 }
 
 pub fn main() {
-    'x: loop { foo!() }
+    'x: loop { foo!(); }
 }

src/test/ui/hygiene/hygienic-label-1.stderr

@@ -4,8 +4,8 @@ error[E0426]: use of undeclared label `'x`
 LL |     () => { break 'x; }
    |                   ^^ undeclared label `'x`
 ...
-LL |     'x: loop { foo!() }
-   |                ------ in this macro invocation
+LL |     'x: loop { foo!(); }
+   |                ------- in this macro invocation
    |
    = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/hygiene/hygienic-label-3.rs

@@ -4,6 +4,6 @@ macro_rules! foo {
 
 pub fn main() {
     'x: for _ in 0..1 {
-        foo!()
+        foo!();
     };
 }

src/test/ui/hygiene/hygienic-label-3.stderr

@@ -4,8 +4,8 @@ error[E0426]: use of undeclared label `'x`
 LL |     () => { break 'x; }
    |                   ^^ undeclared label `'x`
 ...
-LL |         foo!()
-   |         ------ in this macro invocation
+LL |         foo!();
+   |         ------- in this macro invocation
    |
    = note: this error originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/lint/semicolon-in-expressions-from-macros/allow-semicolon-in-expressions-from-macros.rs

@@ -0,0 +1,4 @@
+#[macro_export]
+macro_rules! my_macro {
+    () => { true; }
+}

src/test/ui/lint/semicolon-in-expressions-from-macros/auxiliary/foreign-crate.rs

@@ -0,0 +1,9 @@
+// aux-build:foreign-crate.rs
+// check-pass
+
+extern crate foreign_crate;
+
+// Test that we do not lint for a macro in a foreign crate
+fn main() {
+    let _ = foreign_crate::my_macro!();
+}

src/test/ui/lint/semicolon-in-expressions-from-macros/foreign-crate.rs

@@ -0,0 +1,16 @@
+// check-pass
+// Ensure that trailing semicolons cause warnings by default
+
+macro_rules! foo {
+    () => {
+        true; //~  WARN trailing semicolon in macro
+              //~| WARN this was previously
+    }
+}
+
+fn main() {
+    let _val = match true {
+        true => false,
+        _ => foo!()
+    };
+}

src/test/ui/lint/semicolon-in-expressions-from-macros/warn-semicolon-in-expressions-from-macros.rs

@@ -0,0 +1,16 @@
+warning: trailing semicolon in macro used in expression position
+  --> $DIR/warn-semicolon-in-expressions-from-macros.rs:6:13
+   |
+LL |         true;
+   |             ^
+...
+LL |         _ => foo!()
+   |              ------ in this macro invocation
+   |
+   = note: `#[warn(semicolon_in_expressions_from_macros)]` 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 #79813 <https://github.com/rust-lang/rust/issues/79813>
+   = note: this warning originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+warning: 1 warning emitted
+

src/test/ui/lint/semicolon-in-expressions-from-macros/warn-semicolon-in-expressions-from-macros.stderr

@@ -6,6 +6,8 @@ macro_rules! m {
                             //~| ERROR macro expansion ignores token `;`
                             //~| ERROR cannot find type `i` in this scope
                             //~| ERROR cannot find value `i` in this scope
+                            //~| WARN trailing semicolon in macro
+                            //~| WARN this was previously
 }
 
 fn main() {

src/test/ui/macros/macro-context.rs

@@ -64,7 +64,21 @@ LL |     let i = m!();
    |
    = note: this error originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error: aborting due to 6 previous errors
+warning: trailing semicolon in macro used in expression position
+  --> $DIR/macro-context.rs:3:15
+   |
+LL |     () => ( i ; typeof );
+   |               ^
+...
+LL |     let i = m!();
+   |             ---- in this macro invocation
+   |
+   = note: `#[warn(semicolon_in_expressions_from_macros)]` 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 #79813 <https://github.com/rust-lang/rust/issues/79813>
+   = note: this warning originates in the macro `m` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to 6 previous errors; 1 warning emitted
 
 Some errors have detailed explanations: E0412, E0425.
 For more information about an error, try `rustc --explain E0412`.

src/test/ui/macros/macro-context.stderr

@@ -3,6 +3,12 @@
 macro_rules! foo {
     () => {
         assert_eq!("A", "A");
+        //~^ WARN trailing semicolon in macro
+        //~| WARN this was previously
+        //~| NOTE macro invocations at the end of a block
+        //~| NOTE to ignore the value produced by the macro
+        //~| NOTE for more information
+        //~| NOTE `#[warn(semicolon_in_expressions_from_macros)]` on by default
         assert_eq!("B", "B");
     }
     //~^^ ERROR macro expansion ignores token `assert_eq` and any following
@@ -12,4 +18,10 @@ macro_rules! foo {
 fn main() {
     foo!();
     //~^ NOTE caused by the macro expansion here
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
 }

src/test/ui/macros/macro-in-expression-context.fixed

@@ -3,6 +3,12 @@
 macro_rules! foo {
     () => {
         assert_eq!("A", "A");
+        //~^ WARN trailing semicolon in macro
+        //~| WARN this was previously
+        //~| NOTE macro invocations at the end of a block
+        //~| NOTE to ignore the value produced by the macro
+        //~| NOTE for more information
+        //~| NOTE `#[warn(semicolon_in_expressions_from_macros)]` on by default
         assert_eq!("B", "B");
     }
     //~^^ ERROR macro expansion ignores token `assert_eq` and any following
@@ -12,4 +18,10 @@ macro_rules! foo {
 fn main() {
     foo!()
     //~^ NOTE caused by the macro expansion here
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
+    //~| NOTE in this expansion
 }

src/test/ui/macros/macro-in-expression-context.rs

@@ -1,5 +1,5 @@
 error: macro expansion ignores token `assert_eq` and any following
-  --> $DIR/macro-in-expression-context.rs:6:9
+  --> $DIR/macro-in-expression-context.rs:12:9
    |
 LL |         assert_eq!("B", "B");
    |         ^^^^^^^^^
@@ -11,5 +11,21 @@ LL |     foo!()
    |
    = note: the usage of `foo!` is likely invalid in expression context
 
-error: aborting due to previous error
+warning: trailing semicolon in macro used in expression position
+  --> $DIR/macro-in-expression-context.rs:5:29
+   |
+LL |         assert_eq!("A", "A");
+   |                             ^
+...
+LL |     foo!()
+   |     ------ in this macro invocation
+   |
+   = note: `#[warn(semicolon_in_expressions_from_macros)]` 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 #79813 <https://github.com/rust-lang/rust/issues/79813>
+   = note: macro invocations at the end of a block are treated as expressions
+   = note: to ignore the value produced by the macro, add a semicolon after the invocation of `foo`
+   = note: this warning originates in the macro `foo` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: aborting due to previous error; 1 warning emitted
 

src/test/ui/macros/macro-in-expression-context.stderr

@@ -17,7 +17,7 @@ macro_rules! wrap {
     (first, $e:expr) => { wrap!(second, $e + 1) };
     (second, $e:expr) => { wrap!(third, $e + 2) };
     (third, $e:expr) => {
-        print_bang!($e + 3);
+        print_bang!($e + 3)
     };
 }
 

src/test/ui/proc-macro/nested-nonterminal-tokens.rs

@@ -7,7 +7,7 @@
 fn f1(_: &str) {}
 macro_rules! m1 {
     ($e:expr) => {
-        f1($e);
+        f1($e)
     };
 }
 macro_rules! m3 {

src/tools/clippy/tests/ui/needless_borrow_pat.rs

@@ -7,7 +7,7 @@
 fn f1(_: &str) {}
 macro_rules! m2 {
     ($e:expr) => {
-        f1(*$e);
+        f1(*$e)
     };
 }
 macro_rules! m3 {