derive: avoid parse_in_attr

src/librustc_parse/lib.rs

@@ -285,7 +285,7 @@ pub fn parse_in<'a, T>(
 }
 
 /// Runs the given subparser `f` on the tokens of the given `attr`'s item.
-pub fn parse_in_attr<'a, T>(
+fn parse_in_attr<'a, T>(
     sess: &'a ParseSess,
     attr: &ast::Attribute,
     f: impl FnMut(&mut Parser<'a>) -> PResult<'a, T>,

src/librustc_parse/parser/path.rs

@@ -3,7 +3,6 @@ use crate::maybe_whole;
 use rustc_errors::{PResult, Applicability, pluralize};
 use syntax::ast::{self, QSelf, Path, PathSegment, Ident, ParenthesizedArgs, AngleBracketedArgs};
 use syntax::ast::{AnonConst, GenericArg, AssocTyConstraint, AssocTyConstraintKind, BlockCheckMode};
-use syntax::ast::MacArgs;
 use syntax::ThinVec;
 use syntax::token::{self, Token};
 use syntax_pos::source_map::{Span, BytePos};
@@ -109,42 +108,6 @@ impl<'a> Parser<'a> {
         Ok(Path { segments, span: lo.to(self.prev_span) })
     }
 
-    /// Like `parse_path`, but also supports parsing `Word` meta items into paths for
-    /// backwards-compatibility. This is used when parsing derive macro paths in `#[derive]`
-    /// attributes.
-    fn parse_path_allowing_meta(&mut self, style: PathStyle) -> PResult<'a, Path> {
-        let meta_ident = match self.token.kind {
-            token::Interpolated(ref nt) => match **nt {
-                token::NtMeta(ref item) => match item.args {
-                    MacArgs::Empty => Some(item.path.clone()),
-                    _ => None,
-                },
-                _ => None,
-            },
-            _ => None,
-        };
-        if let Some(path) = meta_ident {
-            self.bump();
-            return Ok(path);
-        }
-        self.parse_path(style)
-    }
-
-    /// Parse a list of paths inside `#[derive(path_0, ..., path_n)]`.
-    pub fn parse_derive_paths(&mut self) -> PResult<'a, Vec<Path>> {
-        self.expect(&token::OpenDelim(token::Paren))?;
-        let mut list = Vec::new();
-        while !self.eat(&token::CloseDelim(token::Paren)) {
-            let path = self.parse_path_allowing_meta(PathStyle::Mod)?;
-            list.push(path);
-            if !self.eat(&token::Comma) {
-                self.expect(&token::CloseDelim(token::Paren))?;
-                break
-            }
-        }
-        Ok(list)
-    }
-
     pub(super) fn parse_path_segments(
         &mut self,
         segments: &mut Vec<PathSegment>,

src/libsyntax_expand/proc_macro.rs

@@ -1,7 +1,7 @@
 use crate::base::{self, *};
 use crate::proc_macro_server;
 
-use syntax::ast::{self, ItemKind, MacArgs};
+use syntax::ast::{self, ItemKind, MetaItemKind, NestedMetaItem};
 use syntax::errors::{Applicability, FatalError};
 use syntax::symbol::sym;
 use syntax::token;
@@ -171,34 +171,71 @@ crate fn collect_derives(cx: &mut ExtCtxt<'_>, attrs: &mut Vec<ast::Attribute>)
         if !attr.has_name(sym::derive) {
             return true;
         }
-        if !attr.is_meta_item_list() {
-            cx.struct_span_err(attr.span, "malformed `derive` attribute input")
-                .span_suggestion(
-                    attr.span,
-                    "missing traits to be derived",
-                    "#[derive(Trait1, Trait2, ...)]".to_owned(),
-                    Applicability::HasPlaceholders,
-                ).emit();
-            return false;
-        }
 
-        let parse_derive_paths = |attr: &ast::Attribute| {
-            if let MacArgs::Empty = attr.get_normal_item().args {
-                return Ok(Vec::new());
+        // 1) First let's ensure that it's a meta item.
+        let nmis = match attr.meta_item_list() {
+            None => {
+                cx.struct_span_err(attr.span, "malformed `derive` attribute input")
+                    .span_suggestion(
+                        attr.span,
+                        "missing traits to be derived",
+                        "#[derive(Trait1, Trait2, ...)]".to_owned(),
+                        Applicability::HasPlaceholders,
+                    )
+                    .emit();
+                return false;
             }
-            rustc_parse::parse_in_attr(cx.parse_sess, attr, |p| p.parse_derive_paths())
+            Some(x) => x,
         };
 
-        match parse_derive_paths(attr) {
-            Ok(traits) => {
-                result.extend(traits);
-                true
-            }
-            Err(mut e) => {
-                e.emit();
-                false
-            }
-        }
+        let mut retain_in_fm = true;
+        let mut retain_in_map = true;
+        let traits = nmis
+            .into_iter()
+            // 2) Moreover, let's ensure we have a path and not `#[derive("foo")]`.
+            .filter_map(|nmi| match nmi {
+                NestedMetaItem::Literal(lit) => {
+                    retain_in_fm = false;
+                    cx.struct_span_err(lit.span, "expected path to a trait, found literal")
+                        .help("for example, write `#[derive(Debug)]` for `Debug`")
+                        .emit();
+                    None
+                }
+                NestedMetaItem::MetaItem(mi) => Some(mi),
+            })
+            // 3) Finally, we only accept `#[derive($path_0, $path_1, ..)]`
+            // but not e.g. `#[derive($path_0 = "value", $path_1(abc))]`.
+            // In this case we can still at least determine that the user
+            // wanted this trait to be derived, so let's keep it.
+            .map(|mi| {
+                let mut traits_dont_accept = |title, action| {
+                    retain_in_map = false;
+                    let sp = mi.span.with_lo(mi.path.span.hi());
+                    cx.struct_span_err(sp, title)
+                        .span_suggestion(
+                            sp,
+                            action,
+                            String::new(),
+                            Applicability::MachineApplicable,
+                        )
+                        .emit();
+                };
+                match &mi.kind {
+                    MetaItemKind::List(..) => traits_dont_accept(
+                        "traits in `#[derive(...)]` don't accept arguments",
+                        "remove the arguments",
+                    ),
+                    MetaItemKind::NameValue(..) => traits_dont_accept(
+                        "traits in `#[derive(...)]` don't accept values",
+                        "remove the value",
+                    ),
+                    MetaItemKind::Word => {}
+                }
+                mi.path
+            });
+
+        result.extend(traits);
+        retain_in_fm && retain_in_map
     });
     result
 }

src/test/ui/malformed/malformed-derive-entry.rs

@@ -1,7 +1,11 @@
-#[derive(Copy(Bad))] //~ ERROR expected one of `)`, `,`, or `::`, found `(`
+#[derive(Copy(Bad))]
+//~^ ERROR traits in `#[derive(...)]` don't accept arguments
+//~| ERROR the trait bound
 struct Test1;
 
-#[derive(Copy="bad")] //~ ERROR expected one of `)`, `,`, or `::`, found `=`
+#[derive(Copy="bad")]
+//~^ ERROR traits in `#[derive(...)]` don't accept values
+//~| ERROR the trait bound
 struct Test2;
 
 #[derive] //~ ERROR malformed `derive` attribute input

src/test/ui/malformed/malformed-derive-entry.stderr

@@ -1,20 +1,33 @@
-error: expected one of `)`, `,`, or `::`, found `(`
+error: traits in `#[derive(...)]` don't accept arguments
   --> $DIR/malformed-derive-entry.rs:1:14
    |
 LL | #[derive(Copy(Bad))]
-   |              ^ expected one of `)`, `,`, or `::`
+   |              ^^^^^ help: remove the arguments
 
-error: expected one of `)`, `,`, or `::`, found `=`
-  --> $DIR/malformed-derive-entry.rs:4:14
+error: traits in `#[derive(...)]` don't accept values
+  --> $DIR/malformed-derive-entry.rs:6:14
    |
 LL | #[derive(Copy="bad")]
-   |              ^ expected one of `)`, `,`, or `::`
+   |              ^^^^^^ help: remove the value
 
 error: malformed `derive` attribute input
-  --> $DIR/malformed-derive-entry.rs:7:1
+  --> $DIR/malformed-derive-entry.rs:11:1
    |
 LL | #[derive]
    | ^^^^^^^^^ help: missing traits to be derived: `#[derive(Trait1, Trait2, ...)]`
 
-error: aborting due to 3 previous errors
+error[E0277]: the trait bound `Test1: std::clone::Clone` is not satisfied
+  --> $DIR/malformed-derive-entry.rs:1:10
+   |
+LL | #[derive(Copy(Bad))]
+   |          ^^^^ the trait `std::clone::Clone` is not implemented for `Test1`
+
+error[E0277]: the trait bound `Test2: std::clone::Clone` is not satisfied
+  --> $DIR/malformed-derive-entry.rs:6:10
+   |
+LL | #[derive(Copy="bad")]
+   |          ^^^^ the trait `std::clone::Clone` is not implemented for `Test2`
+
+error: aborting due to 5 previous errors
 
+For more information about this error, try `rustc --explain E0277`.

src/test/ui/span/macro-ty-params.rs

@@ -10,5 +10,4 @@ fn main() {
     foo::<T>!(); //~ ERROR generic arguments in macro path
     foo::<>!(); //~ ERROR generic arguments in macro path
     m!(Default<>); //~ ERROR generic arguments in macro path
-    //~^ ERROR unexpected generic arguments in path
 }

src/test/ui/span/macro-ty-params.stderr

@@ -10,17 +10,11 @@ error: generic arguments in macro path
 LL |     foo::<>!();
    |          ^^
 
-error: unexpected generic arguments in path
-  --> $DIR/macro-ty-params.rs:12:8
-   |
-LL |     m!(Default<>);
-   |        ^^^^^^^^^
-
 error: generic arguments in macro path
   --> $DIR/macro-ty-params.rs:12:15
    |
 LL |     m!(Default<>);
    |               ^^
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors