Introduce DeriveResolution.

Making this a proper struct, and giving its fields names, makes things
easier to understand.

compiler/rustc_builtin_macros/src/derive.rs

@@ -3,7 +3,9 @@
 
 use rustc_ast as ast;
 use rustc_ast::{GenericParamKind, ItemKind, MetaItemKind, NestedMetaItem, StmtKind};
-use rustc_expand::base::{Annotatable, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier};
+use rustc_expand::base::{
+    Annotatable, DeriveResolution, ExpandResult, ExtCtxt, Indeterminate, MultiItemModifier,
+};
 use rustc_feature::AttributeTemplate;
 use rustc_parse::validate_attr;
 use rustc_session::Session;
@@ -60,7 +62,12 @@ fn expand(
                                 report_path_args(sess, meta);
                                 meta.path.clone()
                             })
-                            .map(|path| (path, dummy_annotatable(), None, self.is_const))
+                            .map(|path| DeriveResolution {
+                                path,
+                                item: dummy_annotatable(),
+                                exts: None,
+                                is_const: self.is_const,
+                            })
                             .collect()
                     }
                     _ => vec![],
@@ -69,15 +76,15 @@ fn expand(
                 // Do not configure or clone items unless necessary.
                 match &mut resolutions[..] {
                     [] => {}
-                    [(_, first_item, ..), others @ ..] => {
+                    [first, others @ ..] => {
-                        *first_item = cfg_eval(
+                        first.item = cfg_eval(
                             sess,
                             features,
                             item.clone(),
                             ecx.current_expansion.lint_node_id,
                         );
-                        for (_, item, _, _) in others {
+                        for other in others {
-                            *item = first_item.clone();
+                            other.item = first.item.clone();
                         }
                     }
                 }

compiler/rustc_expand/src/base.rs

@@ -968,7 +968,12 @@ pub fn expn_data(
 /// Error type that denotes indeterminacy.
 pub struct Indeterminate;
 
-pub type DeriveResolutions = Vec<(ast::Path, Annotatable, Option<Lrc<SyntaxExtension>>, bool)>;
+pub struct DeriveResolution {
+    pub path: ast::Path,
+    pub item: Annotatable,
+    pub exts: Option<Lrc<SyntaxExtension>>,
+    pub is_const: bool,
+}
 
 pub trait ResolverExpand {
     fn next_node_id(&mut self) -> NodeId;
@@ -1011,11 +1016,11 @@ fn resolve_derives(
         &mut self,
         expn_id: LocalExpnId,
         force: bool,
-        derive_paths: &dyn Fn() -> DeriveResolutions,
+        derive_paths: &dyn Fn() -> Vec<DeriveResolution>,
     ) -> Result<(), Indeterminate>;
     /// Take resolutions for paths inside the `#[derive(...)]` attribute with the given `ExpnId`
     /// back from resolver.
-    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions>;
+    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<Vec<DeriveResolution>>;
     /// Path resolution logic for `#[cfg_accessible(path)]`.
     fn cfg_accessible(
         &mut self,

compiler/rustc_expand/src/expand.rs

@@ -482,7 +482,7 @@ pub fn fully_expand_fragment(&mut self, input_fragment: AstFragment) -> AstFragm
                             derive_invocations.reserve(derives.len());
                             derives
                                 .into_iter()
-                                .map(|(path, item, _exts, is_const)| {
+                                .map(|DeriveResolution { path, item, exts: _, is_const }| {
                                     // FIXME: Consider using the derive resolutions (`_exts`)
                                     // instead of enqueuing the derives to be resolved again later.
                                     let expn_id = LocalExpnId::fresh_empty();

compiler/rustc_resolve/src/lib.rs

@@ -38,7 +38,7 @@
 use rustc_data_structures::steal::Steal;
 use rustc_data_structures::sync::{FreezeReadGuard, Lrc};
 use rustc_errors::{Applicability, Diag, ErrCode};
-use rustc_expand::base::{DeriveResolutions, SyntaxExtension, SyntaxExtensionKind};
+use rustc_expand::base::{DeriveResolution, SyntaxExtension, SyntaxExtensionKind};
 use rustc_feature::BUILTIN_ATTRIBUTES;
 use rustc_hir::def::Namespace::{self, *};
 use rustc_hir::def::NonMacroAttrKind;
@@ -959,7 +959,7 @@ enum BuiltinMacroState {
 }
 
 struct DeriveData {
-    resolutions: DeriveResolutions,
+    resolutions: Vec<DeriveResolution>,
     helper_attrs: Vec<(usize, Ident)>,
     has_derive_copy: bool,
 }

compiler/rustc_resolve/src/macros.rs

@@ -15,7 +15,7 @@
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::sync::Lrc;
 use rustc_errors::{Applicability, StashKey};
-use rustc_expand::base::{Annotatable, DeriveResolutions, Indeterminate, ResolverExpand};
+use rustc_expand::base::{Annotatable, DeriveResolution, Indeterminate, ResolverExpand};
 use rustc_expand::base::{SyntaxExtension, SyntaxExtensionKind};
 use rustc_expand::compile_declarative_macro;
 use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
@@ -344,7 +344,7 @@ fn resolve_derives(
         &mut self,
         expn_id: LocalExpnId,
         force: bool,
-        derive_paths: &dyn Fn() -> DeriveResolutions,
+        derive_paths: &dyn Fn() -> Vec<DeriveResolution>,
     ) -> Result<(), Indeterminate> {
         // Block expansion of the container until we resolve all derives in it.
         // This is required for two reasons:
@@ -360,11 +360,11 @@ fn resolve_derives(
             has_derive_copy: false,
         });
         let parent_scope = self.invocation_parent_scopes[&expn_id];
-        for (i, (path, _, opt_ext, _)) in entry.resolutions.iter_mut().enumerate() {
+        for (i, resolution) in entry.resolutions.iter_mut().enumerate() {
-            if opt_ext.is_none() {
+            if resolution.exts.is_none() {
-                *opt_ext = Some(
+                resolution.exts = Some(
                     match self.resolve_macro_path(
-                        path,
+                        &resolution.path,
                         Some(MacroKind::Derive),
                         &parent_scope,
                         true,
@@ -372,7 +372,7 @@ fn resolve_derives(
                     ) {
                         Ok((Some(ext), _)) => {
                             if !ext.helper_attrs.is_empty() {
-                                let last_seg = path.segments.last().unwrap();
+                                let last_seg = resolution.path.segments.last().unwrap();
                                 let span = last_seg.ident.span.normalize_to_macros_2_0();
                                 entry.helper_attrs.extend(
                                     ext.helper_attrs
@@ -416,7 +416,7 @@ fn resolve_derives(
         Ok(())
     }
 
-    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<DeriveResolutions> {
+    fn take_derive_resolutions(&mut self, expn_id: LocalExpnId) -> Option<Vec<DeriveResolution>> {
         self.derive_data.remove(&expn_id).map(|data| data.resolutions)
     }