Enable impl-trait-overcaptures 2024 transition lint (bytecodealliance#9965)

* Enable `impl-trait-overcaptures` 2024 transition lint

This lint detects cases where returning `impl Trait` will work
differently in 2024 than in the current 2021 edition. Ambiguities are
resolved with `use<..>` syntax stabilized in Rust 1.82.0 to mean the
same thing in both editions.

* Fix some more `impl Trait` returns

* Tighten bounds on settings `iter`

* Fix build on 1.82.0

* Fix another capture on MSRV

Author: alexcrichton

Cargo.toml

@@ -189,6 +189,7 @@ rust-2024-guarded-string-incompatible-syntax = 'warn'
 rust-2024-prelude-collisions = 'warn'
 rust-2024-incompatible-pat = 'warn'
 missing-unsafe-on-extern = 'warn'
+impl-trait-overcaptures = 'warn'
 
 # Don't warn about unknown cfgs for pulley
 [workspace.lints.rust.unexpected_cfgs]

cranelift/codegen/meta/src/gen_settings.rs

@@ -76,7 +76,7 @@ fn gen_iterator(group: &SettingGroup, fmt: &mut Formatter) {
     fmtln!(fmt, "impl Flags {");
     fmt.indent(|fmt| {
         fmt.doc_comment("Iterates the setting values.");
-        fmtln!(fmt, "pub fn iter(&self) -> impl Iterator<Item = Value> {");
+        fmtln!(fmt, "pub fn iter(&self) -> impl Iterator<Item = Value> + use<> {");
         fmt.indent(|fmt| {
             fmtln!(fmt, "let mut bytes = [0; {}];", group.settings_size);
             fmtln!(fmt, "bytes.copy_from_slice(&self.bytes[0..{}]);", group.settings_size);

cranelift/codegen/meta/src/pulley.rs

@@ -47,7 +47,7 @@ enum Operand<'a> {
 }
 
 impl Inst<'_> {
-    fn operands(&self) -> impl Iterator<Item = Operand<'_>> {
+    fn operands(&self) -> impl Iterator<Item = Operand<'_>> + use<'_> {
         self.fields
             .iter()
             .map(|(name, ty)| match (*name, *ty) {

cranelift/codegen/src/isa/mod.rs

@@ -211,7 +211,7 @@ impl<T> IsaBuilder<T> {
     }
 
     /// Iterates the available settings in the builder.
-    pub fn iter(&self) -> impl Iterator<Item = settings::Setting> {
+    pub fn iter(&self) -> impl Iterator<Item = settings::Setting> + use<T> {
         self.setup.iter()
     }
 

cranelift/codegen/src/settings.rs

@@ -167,7 +167,7 @@ impl Builder {
     }
 
     /// Iterates the available settings in the builder.
-    pub fn iter(&self) -> impl Iterator<Item = Setting> {
+    pub fn iter(&self) -> impl Iterator<Item = Setting> + use<> {
         let template = self.template;
 
         template.descriptors.iter().map(move |d| {

crates/cranelift/src/debug.rs

@@ -147,7 +147,7 @@ impl<'a> Compilation<'a> {
     /// compilation.
     ///
     /// Each function is additionally accompanied with its module index.
-    fn indexes(&self) -> impl Iterator<Item = (StaticModuleIndex, DefinedFuncIndex)> + '_ {
+    fn indexes(&self) -> impl Iterator<Item = (StaticModuleIndex, DefinedFuncIndex)> + use<'_> {
         self.translations
             .iter()
             .flat_map(|(i, t)| t.module.defined_func_indices().map(move |j| (i, j)))

crates/cranelift/src/debug/transform/expression.rs

@@ -244,7 +244,7 @@ impl CompiledExpression {
         addr_tr: &'a AddressTransform,
         frame_info: Option<&'a FunctionFrameInfo>,
         isa: &'a dyn TargetIsa,
-    ) -> impl Iterator<Item = Result<(write::Address, u64, write::Expression)>> + 'a {
+    ) -> impl Iterator<Item = Result<(write::Address, u64, write::Expression)>> + use<'a> {
         enum BuildWithLocalsResult<'a> {
             Empty,
             Simple(
@@ -747,7 +747,7 @@ impl<'a, 'b> ValueLabelRangesBuilder<'a, 'b> {
         }
     }
 
-    pub fn into_ranges(self) -> impl Iterator<Item = CachedValueLabelRange> {
+    pub fn into_ranges(self) -> impl Iterator<Item = CachedValueLabelRange> + use<> {
         // Ranges with not-enough labels are discarded.
         let processed_labels_len = self.processed_labels.len();
         self.ranges

crates/environ/src/compile/module_types.rs

@@ -308,7 +308,7 @@ impl ModuleTypesBuilder {
     pub fn rec_group_elements(
         &self,
         rec_group: ModuleInternedRecGroupIndex,
-    ) -> impl ExactSizeIterator<Item = ModuleInternedTypeIndex> {
+    ) -> impl ExactSizeIterator<Item = ModuleInternedTypeIndex> + use<> {
         self.types.rec_group_elements(rec_group)
     }
 

crates/environ/src/fact/trampoline.rs

@@ -3069,13 +3069,14 @@ impl<'a> Source<'a> {
 
 impl<'a> Destination<'a> {
     /// Same as `Source::record_field_srcs` but for destinations.
-    fn record_field_dsts<'b>(
+    fn record_field_dsts<'b, I>(
         &'b self,
         types: &'b ComponentTypesBuilder,
-        fields: impl IntoIterator<Item = InterfaceType> + 'b,
-    ) -> impl Iterator<Item = Destination<'b>> + 'b
+        fields: I,
+    ) -> impl Iterator<Item = Destination<'b>> + use<'b, I>
     where
         'a: 'b,
+        I: IntoIterator<Item = InterfaceType> + 'b,
     {
         let mut offset = 0;
         fields.into_iter().map(move |ty| match self {

crates/environ/src/module.rs

@@ -537,7 +537,7 @@ impl Module {
 
     /// Returns an iterator over all of the defined function indices in this
     /// module.
-    pub fn defined_func_indices(&self) -> impl Iterator<Item = DefinedFuncIndex> {
+    pub fn defined_func_indices(&self) -> impl Iterator<Item = DefinedFuncIndex> + use<> {
         (0..self.functions.len() - self.num_imported_funcs).map(|i| DefinedFuncIndex::new(i))
     }