Fix another issue with fixup reversing

We need to *remove* the whole subtree, but we don't advance `i` by this, because it hasn't gotten there yet (and never will).

crates/hir-expand/src/builtin/quote.rs

@@ -102,6 +102,7 @@ macro_rules! quote_impl__ {
     ($span:ident $builder:ident # ) => {$crate::builtin::quote::__quote!(@PUNCT($span $builder) '#')};
     ($span:ident $builder:ident $ ) => {$crate::builtin::quote::__quote!(@PUNCT($span $builder) '$')};
     ($span:ident $builder:ident * ) => {$crate::builtin::quote::__quote!(@PUNCT($span $builder) '*')};
+    ($span:ident $builder:ident = ) => {$crate::builtin::quote::__quote!(@PUNCT($span $builder) '=')};
 
     ($span:ident $builder:ident $first:tt $($tail:tt)+ ) => {{
         $crate::builtin::quote::__quote!($span $builder $first);

crates/hir-expand/src/fixup.rs

@@ -441,8 +441,8 @@ fn transform_tt<'a, 'b>(
                 };
                 let len_diff = replacement.len() as i64 - old_len as i64;
                 tt.splice(i..i + old_len, replacement.flat_tokens().iter().cloned());
-                // `+1` for the loop.
-                i = i.checked_add_signed(len_diff as isize + 1).unwrap();
+                // Skip the newly inserted replacement, we don't want to visit it.
+                i += replacement.len();
 
                 for &subtree_idx in &subtrees_stack {
                     let tt::TokenTree::Subtree(subtree) = &mut tt[subtree_idx] else {

crates/ide/src/inlay_hints.rs

@@ -867,6 +867,19 @@ fn foo() {
     let
     loop {}
 }
+"#,
+        );
+    }
+
+    #[test]
+    fn regression_18898() {
+        check(
+            r#"
+//- proc_macros: issue_18898
+#[proc_macros::issue_18898]
+fn foo() {
+    let
+}
 "#,
         );
     }

crates/test-fixture/src/lib.rs

@@ -376,8 +376,8 @@ impl ChangeFixture {
     }
 }
 
-fn default_test_proc_macros() -> [(String, ProcMacro); 8] {
-    [
+fn default_test_proc_macros() -> Box<[(String, ProcMacro)]> {
+    Box::new([
         (
             r#"
 #[proc_macro_attribute]
@@ -498,7 +498,22 @@ pub fn issue_17479(input: TokenStream) -> TokenStream {
                 disabled: false,
             },
         ),
-    ]
+        (
+            r#"
+#[proc_macro_attribute]
+pub fn issue_18898(_attr: TokenStream, input: TokenStream) -> TokenStream {
+    input
+}
+"#
+            .into(),
+            ProcMacro {
+                name: Symbol::intern("issue_18898"),
+                kind: ProcMacroKind::Bang,
+                expander: sync::Arc::new(Issue18898ProcMacroExpander),
+                disabled: false,
+            },
+        ),
+    ])
 }
 
 fn filter_test_proc_macros(
@@ -801,3 +816,54 @@ impl ProcMacroExpander for Issue17479ProcMacroExpander {
         })
     }
 }
+
+// Reads ident type within string quotes, for issue #17479.
+#[derive(Debug)]
+struct Issue18898ProcMacroExpander;
+impl ProcMacroExpander for Issue18898ProcMacroExpander {
+    fn expand(
+        &self,
+        subtree: &TopSubtree,
+        _: Option<&TopSubtree>,
+        _: &Env,
+        def_site: Span,
+        _: Span,
+        _: Span,
+        _: Option<String>,
+    ) -> Result<TopSubtree, ProcMacroExpansionError> {
+        let span = subtree
+            .token_trees()
+            .flat_tokens()
+            .last()
+            .ok_or_else(|| ProcMacroExpansionError::Panic("malformed input".to_owned()))?
+            .first_span();
+        let overly_long_subtree = quote! {span =>
+            {
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+                let a = 5;
+            }
+        };
+        Ok(quote! { def_site =>
+            fn foo() {
+                #overly_long_subtree
+            }
+        })
+    }
+}