FCW on expressions in doc attributes on macro calls

compiler/rustc_attr_parsing/src/attributes/doc.rs

@@ -1,17 +1,20 @@
-use rustc_ast::ast::{AttrStyle, LitKind, MetaItemLit};
+use rustc_ast::ExprKind;
+use rustc_ast::ast::{self, AttrArgs, AttrKind, AttrStyle, LitKind, MetaItemLit};
 use rustc_attr_ir::target::Target;
 use rustc_attr_ir::{
     AttributeKind, CfgEntry, CfgHideShow, DocAttribute, DocCfgHideShow, DocCfgHideShowValue,
     DocInline, HideOrShow,
 };
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap, IndexEntry};
-use rustc_errors::Applicability;
+use rustc_errors::{Applicability, Diagnostic, MultiSpan};
 use rustc_feature::AttributeStability;
+use rustc_lint_defs::LintId;
 use rustc_lint_defs::builtin::{INVALID_DOC_ATTRIBUTES, UNUSED_ATTRIBUTES};
 use rustc_span::{Span, Symbol, edition, sym};
 
 use super::prelude::{ALL_TARGETS, AllowedTargets};
 use super::{AcceptMapping, AttributeParser, template};
+use crate::EmitAttribute;
 use crate::context::{AcceptContext, FinalizeContext};
 use crate::diagnostics::{
     AttrCrateLevelOnly, DocAliasBadChar, DocAliasDuplicated, DocAliasEmpty, DocAliasMalformed,
@@ -21,7 +24,7 @@ use crate::diagnostics::{
     DocAutoCfgHideShowValuesMix, DocAutoCfgWrongLiteral, DocKeywordNotKeyword, DocTestLiteral,
     DocTestTakesList, DocTestUnknown, DocUnknownAny, DocUnknownInclude, DocUnknownPasses,
     DocUnknownPlugins, DocUnknownSpotlight, ExpectedNameValue, ExpectedNoArgs,
-    IllFormedAttributeInput, MalformedDoc, UnusedDuplicate,
+    IllFormedAttributeInput, InvalidExprInDocAttr, MalformedDoc, UnusedDuplicate,
 };
 use crate::parser::{
     ArgParser, MetaItemListParser, MetaItemOrLitParser, MetaItemParser, OwnedPathParser,
@@ -827,3 +830,41 @@ impl AttributeParser for DocParser {
         }
     }
 }
+
+/// Is this a `#[doc = mac!()]`?
+///
+/// Or perhaps something as spicy as this?
+/// ```ignore,_
+/// #[doc = {
+///     let a = 1;
+///     let b = 1;
+///     let sum = a + b;
+///     assert_eq!(sum, 2);
+/// }]
+/// println!();
+/// ```
+pub(crate) fn lint_non_lit_doc_attr(
+    mut emit_lint: impl FnMut(LintId, MultiSpan, EmitAttribute),
+    attr: &ast::Attribute,
+) -> bool {
+    if !attr.has_name(sym::doc) {
+        return false;
+    }
+    let AttrKind::Normal(n) = &attr.kind else { return false };
+    let AttrArgs::Eq { expr, .. } = &n.item.args else { return false };
+    if matches!(expr.kind, ExprKind::Lit(_)) {
+        return false;
+    };
+
+    let attr_span = attr.span;
+    let expr_span = expr.span;
+
+    emit_lint(
+        LintId::of(rustc_lint_defs::builtin::ILL_FORMED_ATTRIBUTE_INPUT),
+        attr_span.into(),
+        EmitAttribute(Box::new(move |dcx, level, _| {
+            InvalidExprInDocAttr { attr_span, expr_span }.into_diag(dcx, level)
+        })),
+    );
+    true
+}

compiler/rustc_attr_parsing/src/diagnostics.rs

@@ -1345,6 +1345,15 @@ pub(crate) enum InvalidTargetHelp {
     UseRustcAlignStatic,
 }
 
+#[derive(Diagnostic)]
+#[diag("invalid expression in `doc` attribute on macro invocation")]
+pub(crate) struct InvalidExprInDocAttr {
+    #[primary_span]
+    pub expr_span: Span,
+    #[suggestion("remove the attribute", code = "", applicability = "machine-applicable")]
+    pub attr_span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag("invalid alignment value: {$error_part}", code = E0589)]
 pub(crate) struct InvalidAlignmentValue {

compiler/rustc_attr_parsing/src/interface.rs

@@ -16,6 +16,7 @@ use rustc_session::Session;
 use rustc_span::{DUMMY_SP, ErrorGuaranteed, Span, Symbol, sym};
 
 use crate::attributes::AttributeSafety;
+use crate::attributes::doc::lint_non_lit_doc_attr;
 use crate::context::{
     ATTRIBUTE_PARSERS, AcceptContext, FinalizeCheckContext, FinalizeCheckFn, FinalizeContext,
     FinalizeFn, FinalizeOutput, SharedContext,
@@ -332,17 +333,8 @@ impl<'sess> AttributeParser<'sess> {
                 }
             }
 
-            fn is_doc_non_lit_expr(attr: &ast::Attribute) -> bool {
-                if !attr.has_name(sym::doc) {
-                    return false;
-                }
-                let ast::AttrKind::Normal(n) = &attr.kind else { return false };
-                let ast::AttrArgs::Eq { expr, .. } = &n.item.args else { return false };
-                !matches!(expr.kind, ast::ExprKind::Lit(_))
-            }
-
             // FIXME accidentally allowed on Stable Rust
-            if target == Target::MacroCall && is_doc_non_lit_expr(attr) {
+            if target == Target::MacroCall && lint_non_lit_doc_attr(&mut emit_lint, attr) {
                 continue;
             }
 

tests/ui/attributes/attr-on-mac-call.rs

@@ -113,12 +113,22 @@ fn main() {
     #[deprecated = concat!("woah", "dude")]
     //~^ ERROR attribute value must be a literal
     #[doc = concat!("woah", "dude")]
+    //~^ ERROR invalid expression in `doc` attribute on macro invocation
+    //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
     unreachable!();
     #[doc = {
         let a = 1;
         let b = 1;
         let sum = a + b;
         assert_eq!(sum, 2);
     }]
+    //~^^^^^^ ERROR invalid expression in `doc` attribute on macro invocation
+    //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+    unreachable!();
+    #[doc = {
+        let expressions @ r#in @ doc @ attributes @ at = home;
+    }]
+    //~^^^ ERROR invalid expression in `doc` attribute on macro invocation
+    //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
     unreachable!();
 }

tests/ui/attributes/attr-on-mac-call.stderr

@@ -347,6 +347,97 @@ LL |     #[repr(Rust)]
    = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
    = note: placing this attribute on a macro invocation does nothing even if the macro expands to what would be a valid target for the attribute
 
-error: aborting due to 5 previous errors; 30 warnings emitted
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/attr-on-mac-call.rs:115:13
+   |
+LL |     #[doc = concat!("woah", "dude")]
+   |     --------^^^^^^^^^^^^^^^^^^^^^^^- help: remove the attribute
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default
+
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/attr-on-mac-call.rs:119:13
+   |
+LL |        #[doc = {
+   |  ______-       ^
+   | | _____________|
+LL | ||         let a = 1;
+LL | ||         let b = 1;
+LL | ||         let sum = a + b;
+LL | ||         assert_eq!(sum, 2);
+LL | ||     }]
+   | ||_____^- help: remove the attribute
+   |  |_____|
+   |
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/attr-on-mac-call.rs:128:13
+   |
+LL |        #[doc = {
+   |  ______-       ^
+   | | _____________|
+LL | ||         let expressions @ r#in @ doc @ attributes @ at = home;
+LL | ||     }]
+   | ||_____^- help: remove the attribute
+   |  |_____|
+   |
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+
+error: aborting due to 8 previous errors; 30 warnings emitted
 
 For more information about this error, try `rustc --explain E0658`.
+Future incompatibility report: Future breakage diagnostic:
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/attr-on-mac-call.rs:115:13
+   |
+LL |     #[doc = concat!("woah", "dude")]
+   |     --------^^^^^^^^^^^^^^^^^^^^^^^- help: remove the attribute
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/attr-on-mac-call.rs:119:13
+   |
+LL |        #[doc = {
+   |  ______-       ^
+   | | _____________|
+LL | ||         let a = 1;
+LL | ||         let b = 1;
+LL | ||         let sum = a + b;
+LL | ||         assert_eq!(sum, 2);
+LL | ||     }]
+   | ||_____^- help: remove the attribute
+   |  |_____|
+   |
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default
+
+Future breakage diagnostic:
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/attr-on-mac-call.rs:128:13
+   |
+LL |        #[doc = {
+   |  ______-       ^
+   | | _____________|
+LL | ||         let expressions @ r#in @ doc @ attributes @ at = home;
+LL | ||     }]
+   | ||_____^- help: remove the attribute
+   |  |_____|
+   |
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default
+

tests/ui/lint/unused/unused-doc-comments-for-macros.rs

@@ -23,5 +23,7 @@ fn main() {
         assert_eq!(sum, 2);
     }]
     //~^^^^^^ ERROR: unused doc comment
+    //~| ERROR invalid expression in `doc` attribute on macro invocation
+    //~| WARN this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
     foo!();
 }

tests/ui/lint/unused/unused-doc-comments-for-macros.stderr

@@ -27,6 +27,25 @@ LL | |     /// line3
    |
    = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion
 
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/unused-doc-comments-for-macros.rs:19:13
+   |
+LL |        #[doc = {
+   |  ______-       ^
+   | | _____________|
+LL | ||         let a = 1;
+LL | ||         let b = 1;
+LL | ||         let sum = a + b;
+LL | ||         assert_eq!(sum, 2);
+LL | ||     }]
+   | ||_____^- help: remove the attribute
+   |  |_____|
+   |
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default
+
 error: unused doc comment
   --> $DIR/unused-doc-comments-for-macros.rs:19:5
    |
@@ -40,5 +59,25 @@ LL | |     }]
    |
    = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
+
+Future incompatibility report: Future breakage diagnostic:
+error: invalid expression in `doc` attribute on macro invocation
+  --> $DIR/unused-doc-comments-for-macros.rs:19:13
+   |
+LL |        #[doc = {
+   |  ______-       ^
+   | | _____________|
+LL | ||         let a = 1;
+LL | ||         let b = 1;
+LL | ||         let sum = a + b;
+LL | ||         assert_eq!(sum, 2);
+LL | ||     }]
+   | ||_____^- help: remove the attribute
+   |  |_____|
+   |
+   |
+   = 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 #57571 <https://github.com/rust-lang/rust/issues/57571>
+   = note: `#[deny(ill_formed_attribute_input)]` (part of `#[deny(future_incompatible)]`) on by default