internal: Compute inlay hint text edits lazily

Author: Veykril

crates/ide/src/inlay_hints.rs

@@ -1,6 +1,6 @@
 use std::{
     fmt::{self, Write},
-    mem::take,
+    mem::{self, take},
 };
 
 use either::Either;
@@ -297,6 +297,17 @@ pub struct InlayHintsConfig {
     pub closing_brace_hints_min_lines: Option<usize>,
     pub fields_to_resolve: InlayFieldsToResolve,
 }
+impl InlayHintsConfig {
+    fn lazy_text_edit(&self, finish: impl FnOnce() -> TextEdit) -> Lazy<TextEdit> {
+        if self.fields_to_resolve.resolve_text_edits {
+            Lazy::Lazy
+        } else {
+            let edit = finish();
+            never!(edit.is_empty(), "inlay hint produced an empty text edit");
+            Lazy::Computed(edit)
+        }
+    }
+}
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub struct InlayFieldsToResolve {
@@ -408,12 +419,32 @@ pub struct InlayHint {
     /// The actual label to show in the inlay hint.
     pub label: InlayHintLabel,
     /// Text edit to apply when "accepting" this inlay hint.
-    pub text_edit: Option<TextEdit>,
+    pub text_edit: Option<Lazy<TextEdit>>,
     /// Range to recompute inlay hints when trying to resolve for this hint. If this is none, the
     /// hint does not support resolving.
     pub resolve_parent: Option<TextRange>,
 }
 
+/// A type signaling that a value is either computed, or is available for computation.
+#[derive(Clone, Debug)]
+pub enum Lazy<T> {
+    Computed(T),
+    Lazy,
+}
+
+impl<T> Lazy<T> {
+    pub fn computed(self) -> Option<T> {
+        match self {
+            Lazy::Computed(it) => Some(it),
+            _ => None,
+        }
+    }
+
+    pub fn is_lazy(&self) -> bool {
+        matches!(self, Self::Lazy)
+    }
+}
+
 impl std::hash::Hash for InlayHint {
     fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
         self.range.hash(state);
@@ -422,7 +453,7 @@ impl std::hash::Hash for InlayHint {
         self.pad_right.hash(state);
         self.kind.hash(state);
         self.label.hash(state);
-        self.text_edit.is_some().hash(state);
+        mem::discriminant(&self.text_edit).hash(state);
     }
 }
 
@@ -439,10 +470,6 @@ impl InlayHint {
             resolve_parent: None,
         }
     }
-
-    pub fn needs_resolve(&self) -> Option<TextRange> {
-        self.resolve_parent.filter(|_| self.text_edit.is_some() || self.label.needs_resolve())
-    }
 }
 
 #[derive(Debug, Hash)]
@@ -503,10 +530,6 @@ impl InlayHintLabel {
         }
         self.parts.push(part);
     }
-
-    pub fn needs_resolve(&self) -> bool {
-        self.parts.iter().any(|part| part.linked_location.is_some() || part.tooltip.is_some())
-    }
 }
 
 impl From<String> for InlayHintLabel {
@@ -725,19 +748,22 @@ fn hint_iterator(
 
 fn ty_to_text_edit(
     sema: &Semantics<'_, RootDatabase>,
+    config: &InlayHintsConfig,
     node_for_hint: &SyntaxNode,
     ty: &hir::Type,
     offset_to_insert: TextSize,
-    prefix: String,
-) -> Option<TextEdit> {
-    let scope = sema.scope(node_for_hint)?;
+    prefix: impl Into<String>,
+) -> Option<Lazy<TextEdit>> {
     // FIXME: Limit the length and bail out on excess somehow?
-    let rendered = ty.display_source_code(scope.db, scope.module().into(), false).ok()?;
-
-    let mut builder = TextEdit::builder();
-    builder.insert(offset_to_insert, prefix);
-    builder.insert(offset_to_insert, rendered);
-    Some(builder.finish())
+    let rendered = sema
+        .scope(node_for_hint)
+        .and_then(|scope| ty.display_source_code(scope.db, scope.module().into(), false).ok())?;
+    Some(config.lazy_text_edit(|| {
+        let mut builder = TextEdit::builder();
+        builder.insert(offset_to_insert, prefix.into());
+        builder.insert(offset_to_insert, rendered);
+        builder.finish()
+    }))
 }
 
 fn closure_has_block_body(closure: &ast::ClosureExpr) -> bool {
@@ -847,7 +873,7 @@ mod tests {
 
         let edits = inlay_hints
             .into_iter()
-            .filter_map(|hint| hint.text_edit)
+            .filter_map(|hint| hint.text_edit?.computed())
             .reduce(|mut acc, next| {
                 acc.union(next).expect("merging text edits failed");
                 acc
@@ -867,7 +893,8 @@ mod tests {
         let (analysis, file_id) = fixture::file(ra_fixture);
         let inlay_hints = analysis.inlay_hints(&config, file_id, None).unwrap();
 
-        let edits: Vec<_> = inlay_hints.into_iter().filter_map(|hint| hint.text_edit).collect();
+        let edits: Vec<_> =
+            inlay_hints.into_iter().filter_map(|hint| hint.text_edit?.computed()).collect();
 
         assert!(edits.is_empty(), "unexpected edits: {edits:?}");
     }

crates/ide/src/inlay_hints/adjustment.rs

@@ -183,7 +183,7 @@ pub(super) fn hints(
         return None;
     }
     if allow_edit {
-        let edit = {
+        let edit = Some(config.lazy_text_edit(|| {
             let mut b = TextEditBuilder::default();
             if let Some(pre) = &pre {
                 b.insert(
@@ -198,14 +198,14 @@ pub(super) fn hints(
                 );
             }
             b.finish()
-        };
+        }));
         match (&mut pre, &mut post) {
             (Some(pre), Some(post)) => {
-                pre.text_edit = Some(edit.clone());
-                post.text_edit = Some(edit);
+                pre.text_edit = edit.clone();
+                post.text_edit = edit;
             }
-            (Some(pre), None) => pre.text_edit = Some(edit),
-            (None, Some(post)) => post.text_edit = Some(edit),
+            (Some(pre), None) => pre.text_edit = edit,
+            (None, Some(post)) => post.text_edit = edit,
             (None, None) => (),
         }
     }

crates/ide/src/inlay_hints/bind_pat.rs

@@ -78,13 +78,14 @@ pub(super) fn hints(
     let text_edit = if let Some(colon_token) = &type_ascriptable {
         ty_to_text_edit(
             sema,
+            config,
             desc_pat.syntax(),
             &ty,
             colon_token
                 .as_ref()
                 .map_or_else(|| pat.syntax().text_range(), |t| t.text_range())
                 .end(),
-            if colon_token.is_some() { String::new() } else { String::from(": ") },
+            if colon_token.is_some() { "" } else { ": " },
         )
     } else {
         None

crates/ide/src/inlay_hints/binding_mode.rs

@@ -99,17 +99,24 @@ pub(super) fn hints(
     }
 
     if let hints @ [_, ..] = &mut acc[acc_base..] {
-        let mut edit = TextEditBuilder::default();
-        for h in &mut *hints {
-            edit.insert(
-                match h.position {
-                    InlayHintPosition::Before => h.range.start(),
-                    InlayHintPosition::After => h.range.end(),
-                },
-                h.label.parts.iter().map(|p| &*p.text).chain(h.pad_right.then_some(" ")).collect(),
-            );
-        }
-        let edit = edit.finish();
+        let edit = config.lazy_text_edit(|| {
+            let mut edit = TextEditBuilder::default();
+            for h in &mut *hints {
+                edit.insert(
+                    match h.position {
+                        InlayHintPosition::Before => h.range.start(),
+                        InlayHintPosition::After => h.range.end(),
+                    },
+                    h.label
+                        .parts
+                        .iter()
+                        .map(|p| &*p.text)
+                        .chain(h.pad_right.then_some(" "))
+                        .collect(),
+                );
+            }
+            edit.finish()
+        });
         hints.iter_mut().for_each(|h| h.text_edit = Some(edit.clone()));
     }
 

crates/ide/src/inlay_hints/closure_ret.rs

@@ -52,13 +52,14 @@ pub(super) fn hints(
     let text_edit = if has_block_body {
         ty_to_text_edit(
             sema,
+            config,
             closure.syntax(),
             &ty,
             arrow
                 .as_ref()
                 .map_or_else(|| param_list.syntax().text_range(), |t| t.text_range())
                 .end(),
-            if arrow.is_none() { String::from(" -> ") } else { String::new() },
+            if arrow.is_none() { " -> " } else { "" },
         )
     } else {
         None

crates/ide/src/inlay_hints/discriminant.rs

@@ -36,13 +36,14 @@ pub(super) fn enum_hints(
         return None;
     }
     for variant in enum_.variant_list()?.variants() {
-        variant_hints(acc, sema, &enum_, &variant);
+        variant_hints(acc, config, sema, &enum_, &variant);
     }
     Some(())
 }
 
 fn variant_hints(
     acc: &mut Vec<InlayHint>,
+    config: &InlayHintsConfig,
     sema: &Semantics<'_, RootDatabase>,
     enum_: &ast::Enum,
     variant: &ast::Variant,
@@ -88,7 +89,9 @@ fn variant_hints(
         },
         kind: InlayKind::Discriminant,
         label,
-        text_edit: d.ok().map(|val| TextEdit::insert(range.start(), format!("{eq_} {val}"))),
+        text_edit: d.ok().map(|val| {
+            config.lazy_text_edit(|| TextEdit::insert(range.start(), format!("{eq_} {val}")))
+        }),
         position: InlayHintPosition::After,
         pad_left: false,
         pad_right: false,

crates/ide/src/inlay_hints/extern_block.rs

@@ -8,7 +8,7 @@ use crate::{InlayHint, InlayHintsConfig};
 pub(super) fn extern_block_hints(
     acc: &mut Vec<InlayHint>,
     FamousDefs(_sema, _): &FamousDefs<'_, '_>,
-    _config: &InlayHintsConfig,
+    config: &InlayHintsConfig,
     _file_id: EditionedFileId,
     extern_block: ast::ExternBlock,
 ) -> Option<()> {
@@ -23,7 +23,9 @@ pub(super) fn extern_block_hints(
         pad_right: true,
         kind: crate::InlayKind::ExternUnsafety,
         label: crate::InlayHintLabel::from("unsafe"),
-        text_edit: Some(TextEdit::insert(abi.syntax().text_range().start(), "unsafe ".to_owned())),
+        text_edit: Some(config.lazy_text_edit(|| {
+            TextEdit::insert(abi.syntax().text_range().start(), "unsafe ".to_owned())
+        })),
         resolve_parent: Some(extern_block.syntax().text_range()),
     });
     Some(())
@@ -32,7 +34,7 @@ pub(super) fn extern_block_hints(
 pub(super) fn fn_hints(
     acc: &mut Vec<InlayHint>,
     FamousDefs(_sema, _): &FamousDefs<'_, '_>,
-    _config: &InlayHintsConfig,
+    config: &InlayHintsConfig,
     _file_id: EditionedFileId,
     fn_: &ast::Fn,
     extern_block: &ast::ExternBlock,
@@ -42,14 +44,14 @@ pub(super) fn fn_hints(
         return None;
     }
     let fn_ = fn_.fn_token()?;
-    acc.push(item_hint(extern_block, fn_));
+    acc.push(item_hint(config, extern_block, fn_));
     Some(())
 }
 
 pub(super) fn static_hints(
     acc: &mut Vec<InlayHint>,
     FamousDefs(_sema, _): &FamousDefs<'_, '_>,
-    _config: &InlayHintsConfig,
+    config: &InlayHintsConfig,
     _file_id: EditionedFileId,
     static_: &ast::Static,
     extern_block: &ast::ExternBlock,
@@ -59,28 +61,32 @@ pub(super) fn static_hints(
         return None;
     }
     let static_ = static_.static_token()?;
-    acc.push(item_hint(extern_block, static_));
+    acc.push(item_hint(config, extern_block, static_));
     Some(())
 }
 
-fn item_hint(extern_block: &ast::ExternBlock, token: SyntaxToken) -> InlayHint {
+fn item_hint(
+    config: &InlayHintsConfig,
+    extern_block: &ast::ExternBlock,
+    token: SyntaxToken,
+) -> InlayHint {
     InlayHint {
         range: token.text_range(),
         position: crate::InlayHintPosition::Before,
         pad_left: false,
         pad_right: true,
         kind: crate::InlayKind::ExternUnsafety,
         label: crate::InlayHintLabel::from("unsafe"),
-        text_edit: {
+        text_edit: Some(config.lazy_text_edit(|| {
             let mut builder = TextEdit::builder();
             builder.insert(token.text_range().start(), "unsafe ".to_owned());
             if extern_block.unsafe_token().is_none() {
                 if let Some(abi) = extern_block.abi() {
                     builder.insert(abi.syntax().text_range().start(), "unsafe ".to_owned());
                 }
             }
-            Some(builder.finish())
-        },
+            builder.finish()
+        })),
         resolve_parent: Some(extern_block.syntax().text_range()),
     }
 }

crates/ide/src/inlay_hints/implicit_static.rs

@@ -39,7 +39,9 @@ pub(super) fn hints(
                 range: t.text_range(),
                 kind: InlayKind::Lifetime,
                 label: "'static".into(),
-                text_edit: Some(TextEdit::insert(t.text_range().start(), "'static ".into())),
+                text_edit: Some(config.lazy_text_edit(|| {
+                    TextEdit::insert(t.text_range().start(), "'static ".into())
+                })),
                 position: InlayHintPosition::After,
                 pad_left: false,
                 pad_right: true,

crates/rust-analyzer/src/lsp/to_proto.rs

@@ -547,7 +547,18 @@ pub(crate) fn inlay_hint(
     file_id: FileId,
     mut inlay_hint: InlayHint,
 ) -> Cancellable<lsp_types::InlayHint> {
-    let resolve_range_and_hash = inlay_hint.needs_resolve().map(|range| {
+    let hint_needs_resolve = |hint: &InlayHint| -> Option<TextRange> {
+        hint.resolve_parent.filter(|_| {
+            hint.text_edit.is_some()
+                || hint
+                    .label
+                    .parts
+                    .iter()
+                    .any(|part| part.linked_location.is_some() || part.tooltip.is_some())
+        })
+    };
+
+    let resolve_range_and_hash = hint_needs_resolve(&inlay_hint).map(|range| {
         (
             range,
             std::hash::BuildHasher::hash_one(
@@ -568,7 +579,11 @@ pub(crate) fn inlay_hint(
         something_to_resolve |= inlay_hint.text_edit.is_some();
         None
     } else {
-        inlay_hint.text_edit.take().map(|it| text_edit_vec(line_index, it))
+        inlay_hint
+            .text_edit
+            .take()
+            .and_then(|it| it.computed())
+            .map(|it| text_edit_vec(line_index, it))
     };
     let (label, tooltip) = inlay_hint_label(
         snap,