Add tooltips to a closure (#2164)

3 files changed, 60 insertions, 26 deletions

diff --git a/crates/typst/src/eval/func.rs b/crates/typst/src/eval/func.rs
index 3e4ea370..87237352 100644
--- a/crates/typst/src/eval/func.rs
+++ b/crates/typst/src/eval/func.rs
@@ -597,15 +597,15 @@ cast! {
 }
 
 /// A visitor that determines which variables to capture for a closure.
-pub(super) struct CapturesVisitor<'a> {
-    external: &'a Scopes<'a>,
+pub struct CapturesVisitor<'a> {
+    external: Option<&'a Scopes<'a>>,
     internal: Scopes<'a>,
     captures: Scope,
 }
 
 impl<'a> CapturesVisitor<'a> {
     /// Create a new visitor for the given external scopes.
-    pub fn new(external: &'a Scopes) -> Self {
+    pub fn new(external: Option<&'a Scopes<'a>>) -> Self {
         Self {
             external,
             internal: Scopes::new(None),
@@ -626,8 +626,10 @@ impl<'a> CapturesVisitor<'a> {
             // Identifiers that shouldn't count as captures because they
             // actually bind a new name are handled below (individually through
             // the expressions that contain them).
-            Some(ast::Expr::Ident(ident)) => self.capture(ident),
-            Some(ast::Expr::MathIdent(ident)) => self.capture_in_math(ident),
+            Some(ast::Expr::Ident(ident)) => self.capture(&ident, Scopes::get),
+            Some(ast::Expr::MathIdent(ident)) => {
+                self.capture(&ident, Scopes::get_in_math)
+            }
 
             // Code and content blocks create a scope.
             Some(ast::Expr::Code(_) | ast::Expr::Content(_)) => {
@@ -736,20 +738,22 @@ impl<'a> CapturesVisitor<'a> {
     }
 
     /// Capture a variable if it isn't internal.
-    fn capture(&mut self, ident: ast::Ident) {
-        if self.internal.get(&ident).is_err() {
-            if let Ok(value) = self.external.get(&ident) {
-                self.captures.define_captured(ident.get().clone(), value.clone());
-            }
-        }
-    }
-
-    /// Capture a variable in math mode if it isn't internal.
-    fn capture_in_math(&mut self, ident: ast::MathIdent) {
-        if self.internal.get(&ident).is_err() {
-            if let Ok(value) = self.external.get_in_math(&ident) {
-                self.captures.define_captured(ident.get().clone(), value.clone());
-            }
+    #[inline]
+    fn capture(
+        &mut self,
+        ident: &str,
+        getter: impl FnOnce(&'a Scopes<'a>, &str) -> StrResult<&'a Value>,
+    ) {
+        if self.internal.get(ident).is_err() {
+            let Some(value) = self
+                .external
+                .map(|external| getter(external, ident).ok())
+                .unwrap_or(Some(&Value::None))
+            else {
+                return;
+            };
+
+            self.captures.define_captured(ident, value.clone());
         }
     }
 }
@@ -767,7 +771,7 @@ mod tests {
         scopes.top.define("y", 0);
         scopes.top.define("z", 0);
 
-        let mut visitor = CapturesVisitor::new(&scopes);
+        let mut visitor = CapturesVisitor::new(Some(&scopes));
         let root = parse(text);
         visitor.visit(&root);
 
diff --git a/crates/typst/src/eval/mod.rs b/crates/typst/src/eval/mod.rs
index cbd00bc1..da0aadd0 100644
--- a/crates/typst/src/eval/mod.rs
+++ b/crates/typst/src/eval/mod.rs
@@ -50,7 +50,9 @@ pub use self::cast::{
 pub use self::datetime::Datetime;
 pub use self::dict::{dict, Dict};
 pub use self::duration::Duration;
-pub use self::func::{func, Func, NativeFunc, NativeFuncData, ParamInfo};
+pub use self::func::{
+    func, CapturesVisitor, Func, NativeFunc, NativeFuncData, ParamInfo,
+};
 pub use self::library::{set_lang_items, LangItems, Library};
 pub use self::module::Module;
 pub use self::none::NoneValue;
@@ -74,7 +76,7 @@ use if_chain::if_chain;
 use serde::{Deserialize, Serialize};
 use unicode_segmentation::UnicodeSegmentation;
 
-use self::func::{CapturesVisitor, Closure};
+use self::func::Closure;
 use crate::diag::{
     bail, error, warning, At, FileError, Hint, SourceDiagnostic, SourceResult, StrResult,
     Trace, Tracepoint,
@@ -1340,7 +1342,7 @@ impl Eval for ast::Closure<'_> {
 
         // Collect captured variables.
         let captured = {
-            let mut visitor = CapturesVisitor::new(&vm.scopes);
+            let mut visitor = CapturesVisitor::new(Some(&vm.scopes));
             visitor.visit(self.to_untyped());
             visitor.finish()
         };
diff --git a/crates/typst/src/ide/tooltip.rs b/crates/typst/src/ide/tooltip.rs
index f310cad0..6f8c8927 100644
--- a/crates/typst/src/ide/tooltip.rs
+++ b/crates/typst/src/ide/tooltip.rs
@@ -7,10 +7,11 @@ use if_chain::if_chain;
 use super::analyze::analyze_labels;
 use super::{analyze_expr, plain_docs_sentence, summarize_font_family};
 use crate::doc::Frame;
-use crate::eval::{CastInfo, Tracer, Value};
+use crate::eval::{CapturesVisitor, CastInfo, Tracer, Value};
 use crate::geom::{round_2, Length, Numeric};
-use crate::syntax::{ast, LinkedNode, Source, SyntaxKind};
-use crate::util::pretty_comma_list;
+use crate::syntax::ast::{self, AstNode};
+use crate::syntax::{LinkedNode, Source, SyntaxKind};
+use crate::util::{pretty_comma_list, separated_list};
 use crate::World;
 
 /// Describe the item under the cursor.
@@ -29,6 +30,7 @@ pub fn tooltip(
         .or_else(|| font_tooltip(world, &leaf))
         .or_else(|| ref_tooltip(world, frames, &leaf))
         .or_else(|| expr_tooltip(world, &leaf))
+        .or_else(|| closure_tooltip(&leaf))
 }
 
 /// A hover tooltip.
@@ -100,6 +102,32 @@ fn expr_tooltip(world: &(dyn World + 'static), leaf: &LinkedNode) -> Option<Tool
     (!tooltip.is_empty()).then(|| Tooltip::Code(tooltip.into()))
 }
 
+/// Tooltip for a hovered closure.
+fn closure_tooltip(leaf: &LinkedNode) -> Option<Tooltip> {
+    // Find the closure to analyze.
+    let mut ancestor = leaf;
+    while !ancestor.is::<ast::Closure>() {
+        ancestor = ancestor.parent()?;
+    }
+    let closure = ancestor.cast::<ast::Closure>()?.to_untyped();
+
+    // Analyze the closure's captures.
+    let mut visitor = CapturesVisitor::new(None);
+    visitor.visit(closure);
+
+    let captures = visitor.finish();
+    let mut names: Vec<_> =
+        captures.iter().map(|(name, _)| eco_format!("`{name}`")).collect();
+    if names.is_empty() {
+        return None;
+    }
+
+    names.sort();
+
+    let tooltip = separated_list(&names, "and");
+    Some(Tooltip::Text(eco_format!("This closure captures {tooltip}.")))
+}
+
 /// Tooltip text for a hovered length.
 fn length_tooltip(length: Length) -> Option<Tooltip> {
     length.em.is_zero().then(|| {