Rollup merge of rust-lang#128224 - nnethercote:fewer-replace_ranges, r=petrochenkov

Remove unnecessary range replacements

This PR removes an unnecessary range replacement in `collect_tokens_trailing_token`, and does a couple of other small cleanups.

r? `@petrochenkov`

Author: matthiaskrgr

compiler/rustc_parse/src/parser/attr_wrapper.rs

@@ -110,17 +110,15 @@ impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
             replace_ranges.sort_by_key(|(range, _)| range.start);
 
             #[cfg(debug_assertions)]
-            {
-                for [(range, tokens), (next_range, next_tokens)] in replace_ranges.array_windows() {
-                    assert!(
-                        range.end <= next_range.start || range.end >= next_range.end,
-                        "Replace ranges should either be disjoint or nested: ({:?}, {:?}) ({:?}, {:?})",
-                        range,
-                        tokens,
-                        next_range,
-                        next_tokens,
-                    );
-                }
+            for [(range, tokens), (next_range, next_tokens)] in replace_ranges.array_windows() {
+                assert!(
+                    range.end <= next_range.start || range.end >= next_range.end,
+                    "Replace ranges should either be disjoint or nested: ({:?}, {:?}) ({:?}, {:?})",
+                    range,
+                    tokens,
+                    next_range,
+                    next_tokens,
+                );
             }
 
             // Process the replace ranges, starting from the highest start
@@ -133,9 +131,9 @@ impl ToAttrTokenStream for LazyAttrTokenStreamImpl {
             // `#[cfg(FALSE)] struct Foo { #[cfg(FALSE)] field: bool }`
             //
             // By starting processing from the replace range with the greatest
-            // start position, we ensure that any replace range which encloses
-            // another replace range will capture the *replaced* tokens for the inner
-            // range, not the original tokens.
+            // start position, we ensure that any (outer) replace range which
+            // encloses another (inner) replace range will fully overwrite the
+            // inner range's replacement.
             for (range, target) in replace_ranges.into_iter().rev() {
                 assert!(!range.is_empty(), "Cannot replace an empty range: {range:?}");
 
@@ -293,11 +291,13 @@ impl<'a> Parser<'a> {
         // with `None`, which means the relevant tokens will be removed. (More
         // details below.)
         let mut inner_attr_replace_ranges = Vec::new();
-        for inner_attr in ret.attrs().iter().filter(|a| a.style == ast::AttrStyle::Inner) {
-            if let Some(attr_range) = self.capture_state.inner_attr_ranges.remove(&inner_attr.id) {
-                inner_attr_replace_ranges.push((attr_range, None));
-            } else {
-                self.dcx().span_delayed_bug(inner_attr.span, "Missing token range for attribute");
+        for attr in ret.attrs() {
+            if attr.style == ast::AttrStyle::Inner {
+                if let Some(attr_range) = self.capture_state.inner_attr_ranges.remove(&attr.id) {
+                    inner_attr_replace_ranges.push((attr_range, None));
+                } else {
+                    self.dcx().span_delayed_bug(attr.span, "Missing token range for attribute");
+                }
             }
         }
 
@@ -333,8 +333,7 @@ impl<'a> Parser<'a> {
         // When parsing `m`:
         // - `start_pos..end_pos` is `0..34` (`mod m`, excluding the `#[cfg_eval]` attribute).
         // - `inner_attr_replace_ranges` is empty.
-        // - `replace_range_start..replace_ranges_end` has two entries.
-        //   - One to delete the inner attribute (`17..27`), obtained when parsing `g` (see above).
+        // - `replace_range_start..replace_ranges_end` has one entry.
         //   - One `AttrsTarget` (added below when parsing `g`) to replace all of `g` (`3..33`,
         //     including its outer attribute), with:
         //     - `attrs`: includes the outer and the inner attr.
@@ -365,12 +364,10 @@ impl<'a> Parser<'a> {
 
             // What is the status here when parsing the example code at the top of this method?
             //
-            // When parsing `g`, we add two entries:
+            // When parsing `g`, we add one entry:
             // - The `start_pos..end_pos` (`3..33`) entry has a new `AttrsTarget` with:
             //   - `attrs`: includes the outer and the inner attr.
             //   - `tokens`: lazy tokens for `g` (with its inner attr deleted).
-            // - `inner_attr_replace_ranges` contains the one entry to delete the inner attr's
-            //   tokens (`17..27`).
             //
             // When parsing `m`, we do nothing here.
 
@@ -380,7 +377,6 @@ impl<'a> Parser<'a> {
             let start_pos = if has_outer_attrs { attrs.start_pos } else { start_pos };
             let target = AttrsTarget { attrs: ret.attrs().iter().cloned().collect(), tokens };
             self.capture_state.replace_ranges.push((start_pos..end_pos, Some(target)));
-            self.capture_state.replace_ranges.extend(inner_attr_replace_ranges);
         } else if matches!(self.capture_state.capturing, Capturing::No) {
             // Only clear the ranges once we've finished capturing entirely, i.e. we've finished
             // the outermost call to this method.