feat: complete parameters by capture information (#1114)

* feat: complete parameters by capture information

* dev: wording

crates/tinymist-query/src/analysis/completion.rs

@@ -507,7 +507,7 @@ impl CompletionPair<'_, '_, '_> {
 
         // Special completions 3, we should remove them finally
         if matches!(surrounding_syntax, ParamList) {
-            return self.complete_params().then_some(());
+            return self.complete_params();
         }
 
         // Checks and completes `self.cursor.syntax_context`

crates/tinymist-query/src/analysis/completion/param.rs

@@ -3,10 +3,59 @@
 //! Note, this is used for the completion of parameters on a function's
 //! *definition* instead of the completion of arguments of some *function call*.
 
+use typst::eval::CapturesVisitor;
+
 use super::*;
 impl CompletionPair<'_, '_, '_> {
     /// Complete parameters.
-    pub fn complete_params(&mut self) -> bool {
-        true
+    pub fn complete_params(&mut self) -> Option<()> {
+        self.cursor.from = self.cursor.leaf.offset();
+
+        let leaf = self.cursor.leaf.clone();
+        let closure_node = node_ancestors(&leaf).find(|node| node.kind() == SyntaxKind::Closure)?;
+
+        let mut bindings = HashSet::<EcoString>::default();
+
+        let closure_node = closure_node.cast::<ast::Closure>()?;
+
+        // It is common for a function to reference itself in typst.
+        let name = closure_node.name();
+        if let Some(name) = name {
+            bindings.insert(name.get().clone());
+        }
+
+        // Collects all bindings from the parameters.
+        let param_list = closure_node.params();
+        for param in param_list.children() {
+            match param {
+                ast::Param::Pos(pos) => {
+                    for name in pos.bindings() {
+                        bindings.insert(name.get().clone());
+                    }
+                }
+                ast::Param::Named(named) => {
+                    bindings.insert(named.name().get().clone());
+                }
+                ast::Param::Spread(spread) => {
+                    if let Some(ident) = spread.sink_ident() {
+                        bindings.insert(ident.get().clone());
+                    }
+                }
+            }
+        }
+
+        let mut visitor = CapturesVisitor::new(None, typst::foundations::Capturer::Function);
+        visitor.visit(closure_node.body().to_untyped());
+        let captures = visitor.finish();
+
+        // Converts the captures into completions.
+        for (name, value, _) in captures.iter() {
+            if !bindings.contains(name) {
+                let docs = "Parametrizes the captured variable.";
+                self.value_completion(Some(name.clone()), value, false, Some(docs));
+            }
+        }
+
+        Some(())
     }
 }

crates/tinymist-query/src/fixtures/completion/param_capture.typ

@@ -0,0 +1,5 @@
+/// contains: content
+
+#let f(
+  content, /* range -6..-5 */
+) = content-ext

crates/tinymist-query/src/fixtures/completion/param_capture_recursive.typ

@@ -0,0 +1,5 @@
+/// contains: function
+
+#let function(
+  fun, /* range -3..-2 */
+) = function

crates/tinymist-query/src/fixtures/completion/param_name.typ

@@ -1,5 +1,5 @@
-/// contains: content
+/// contains: value
 
 #let f(
-  content, /* range -6..-5 */
-) = content
+  val, /* range -3..-2 */
+) = value

crates/tinymist-query/src/fixtures/completion/snaps/test@param_capture.typ.snap

@@ -0,0 +1,13 @@
+---
+source: crates/tinymist-query/src/completion.rs
+description: Completion on t (36..37)
+expression: "JsonRepr::new_pure(results)"
+input_file: crates/tinymist-query/src/fixtures/completion/param_capture.typ
+snapshot_kind: text
+---
+[
+ {
+  "isIncomplete": false,
+  "items": []
+ }
+]

crates/tinymist-query/src/fixtures/completion/snaps/test@param_capture_recursive.typ.snap

@@ -0,0 +1,13 @@
+---
+source: crates/tinymist-query/src/completion.rs
+description: Completion on n (43..44)
+expression: "JsonRepr::new_pure(results)"
+input_file: crates/tinymist-query/src/fixtures/completion/param_capture_recursive.typ
+snapshot_kind: text
+---
+[
+ {
+  "isIncomplete": false,
+  "items": []
+ }
+]

crates/tinymist-query/src/fixtures/completion/snaps/test@param_name.typ.snap

@@ -1,6 +1,6 @@
 ---
 source: crates/tinymist-query/src/completion.rs
-description: Completion on t (36..37)
+description: Completion on l (33..34)
 expression: "JsonRepr::new_pure(results)"
 input_file: crates/tinymist-query/src/fixtures/completion/param_name.typ
 snapshot_kind: text
@@ -8,6 +8,24 @@ snapshot_kind: text
 [
  {
   "isIncomplete": false,
-  "items": []
+  "items": [
+   {
+    "kind": 6,
+    "label": "value",
+    "textEdit": {
+     "newText": "value, ",
+     "range": {
+      "end": {
+       "character": 4,
+       "line": 3
+      },
+      "start": {
+       "character": 2,
+       "line": 3
+      }
+     }
+    }
+   }
+  ]
  }
 ]