Improve suggestions for malformed deprecated attribute

compiler/rustc_attr_parsing/src/attributes/deprecation.rs

@@ -1,3 +1,4 @@
+use rustc_ast::LitKind;
 use rustc_hir::attrs::{DeprecatedSince, Deprecation};
 use rustc_hir::{RustcVersion, VERSION_PLACEHOLDER};
 
@@ -76,6 +77,38 @@ impl SingleAttributeParser for DeprecatedParser {
                 // ok
             }
             ArgParser::List(list) => {
+                // If the argument list contains a single string literal:
+                // check whether it may be a version and suggest since field
+                // otherwise, suggest using NameValue syntax
+                if let Some(elem) = list.as_single()
+                    && let Some(lit) = elem.as_lit()
+                    && let LitKind::Str(text, _) = lit.kind
+                {
+                    let mut adcx = cx.adcx();
+
+                    match parse_since(text, true) {
+                        DeprecatedSince::Future | DeprecatedSince::RustcVersion(_) => {
+                            adcx.push_suggestion(
+                                String::from("try specifying a deprecated since version"),
+                                elem.span(),
+                                format!("since = {}", lit.kind),
+                            );
+                        }
+                        _ => {
+                            if let Some(span) = args.span() {
+                                adcx.push_suggestion(
+                                    String::from("try using `=` instead"),
+                                    span,
+                                    format!(" = {}", lit.kind),
+                                );
+                            }
+                        }
+                    };
+
+                    adcx.expected_not_literal(elem.span());
+                    return None;
+                }
+
                 for param in list.mixed() {
                     let Some(param) = param.meta_item() else {
                         cx.adcx().expected_not_literal(param.span());
@@ -133,18 +166,11 @@ impl SingleAttributeParser for DeprecatedParser {
         }
 
         let since = if let Some(since) = since {
-            if since.as_str() == "TBD" {
-                DeprecatedSince::Future
-            } else if !is_rustc {
-                DeprecatedSince::NonStandard(since)
-            } else if since.as_str() == VERSION_PLACEHOLDER {
-                DeprecatedSince::RustcVersion(RustcVersion::CURRENT)
-            } else if let Some(version) = parse_version(since) {
-                DeprecatedSince::RustcVersion(version)
-            } else {
+            let since = parse_since(since, is_rustc);
+            if matches!(since, DeprecatedSince::Err) {
                 cx.emit_err(InvalidSince { span: cx.attr_span });
-                DeprecatedSince::Err
             }
+            since
         } else if is_rustc {
             cx.emit_err(MissingSince { span: cx.attr_span });
             DeprecatedSince::Err
@@ -163,3 +189,17 @@ impl SingleAttributeParser for DeprecatedParser {
         })
     }
 }
+
+fn parse_since(since: Symbol, is_rustc: bool) -> DeprecatedSince {
+    if since.as_str() == "TBD" {
+        DeprecatedSince::Future
+    } else if !is_rustc {
+        DeprecatedSince::NonStandard(since)
+    } else if since.as_str() == VERSION_PLACEHOLDER {
+        DeprecatedSince::RustcVersion(RustcVersion::CURRENT)
+    } else if let Some(version) = parse_version(since) {
+        DeprecatedSince::RustcVersion(version)
+    } else {
+        DeprecatedSince::Err
+    }
+}

tests/ui/deprecation/deprecation-sanity.rs

@@ -23,6 +23,9 @@ mod bogus_attribute_types_1 {
 
     #[deprecated("test")] //~ ERROR malformed `deprecated` attribute input [E0565]
     fn f8() { }
+
+    #[deprecated("1.2.3")] //~ ERROR malformed `deprecated` attribute input [E0565]
+    fn f9() { }
 }
 
 #[deprecated(since = "a", note = "b")]

tests/ui/deprecation/deprecation-sanity.stderr

@@ -55,29 +55,48 @@ LL |     #[deprecated("test")]
    |     ^^^^^^^^^^^^^------^^
    |                  |
    |                  didn't expect a literal here
+   |
+help: try using `=` instead
+   |
+LL -     #[deprecated("test")]
+LL +     #[deprecated = "test"]
+   |
+
+error[E0565]: malformed `deprecated` attribute input
+  --> $DIR/deprecation-sanity.rs:27:5
+   |
+LL |     #[deprecated("1.2.3")]
+   |     ^^^^^^^^^^^^^-------^^
+   |                  |
+   |                  didn't expect a literal here
+   |
+help: try specifying a deprecated since version
+   |
+LL |     #[deprecated(since = "1.2.3")]
+   |                  +++++++
 
 error: multiple `deprecated` attributes
-  --> $DIR/deprecation-sanity.rs:29:1
+  --> $DIR/deprecation-sanity.rs:32:1
    |
 LL | #[deprecated(since = "a", note = "b")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ help: remove this attribute
    |
 note: attribute also specified here
-  --> $DIR/deprecation-sanity.rs:28:1
+  --> $DIR/deprecation-sanity.rs:31:1
    |
 LL | #[deprecated(since = "a", note = "b")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0538]: malformed `deprecated` attribute input
-  --> $DIR/deprecation-sanity.rs:32:1
+  --> $DIR/deprecation-sanity.rs:35:1
    |
 LL | #[deprecated(since = "a", since = "b", note = "c")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^-----------^^^^^^^^^^^^^^
    |                           |
    |                           found `since` used as a key more than once
 
 error: `#[deprecated]` attribute cannot be used on trait impl blocks
-  --> $DIR/deprecation-sanity.rs:37:1
+  --> $DIR/deprecation-sanity.rs:40:1
    |
 LL | #[deprecated = "hello"]
    | ^^^^^^^^^^^^^^^^^^^^^^^
@@ -86,7 +105,7 @@ LL | #[deprecated = "hello"]
    = help: `#[deprecated]` can be applied to associated consts, associated types, constants, crates, data types, enum variants, foreign statics, functions, inherent impl blocks, macro defs, modules, statics, struct fields, traits, type aliases, and use statements
    = note: `#[deny(useless_deprecated)]` on by default
 
-error: aborting due to 10 previous errors
+error: aborting due to 11 previous errors
 
 Some errors have detailed explanations: E0538, E0539, E0565.
 For more information about an error, try `rustc --explain E0538`.

tests/ui/error-codes/E0565-1.stderr

@@ -5,6 +5,12 @@ LL | #[deprecated("since")]
    | ^^^^^^^^^^^^^-------^^
    |              |
    |              didn't expect a literal here
+   |
+help: try using `=` instead
+   |
+LL - #[deprecated("since")]
+LL + #[deprecated = "since"]
+   |
 
 error: aborting due to 1 previous error