fix: equation code action is broken since v0.13 (#1561)

Todo: discuss the correct behavior on `$ | $` and `$ |$` where `|` are
the cursors.

Author: Myriad-Dreamin

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

@@ -488,10 +488,25 @@ impl<'a> CodeActionWorker<'a> {
         Some(())
     }
 
+    /// Whether the equation should be displayed as a separate block.
+    fn math_is_block(equation: ast::Equation) -> bool {
+        let is_space =
+            |node: Option<&SyntaxNode>| node.map(SyntaxNode::kind) == Some(SyntaxKind::Space);
+        let eq = equation.to_untyped();
+
+        let mut nodes = eq.children().skip(1);
+        let mut first = nodes.next();
+        if first.is_some_and(|first| first.is_empty() && matches!(first.kind(), SyntaxKind::Math)) {
+            first = nodes.next();
+        }
+
+        is_space(first) && is_space(eq.children().nth_back(1))
+    }
+
     fn equation_actions(&mut self, node: &LinkedNode) -> Option<()> {
         let equation = node.cast::<ast::Equation>()?;
         let body = equation.body();
-        let is_block = equation.block();
+        let is_block = Self::math_is_block(equation);
 
         let body = node.find(body.span())?;
         let body_range = body.range();

crates/tinymist-query/src/fixtures/code_action/equation_block.typ

@@ -0,0 +1 @@
+$  $/* range -1..-1 */

crates/tinymist-query/src/fixtures/code_action/equation_block2.typ

@@ -0,0 +1 @@
+$ $/* range -1..-1 */

crates/tinymist-query/src/fixtures/code_action/equation_block3.typ

@@ -0,0 +1 @@
+$ a $/* range -1..-1 */

crates/tinymist-query/src/fixtures/code_action/equation_block4.typ

@@ -0,0 +1 @@
+$ a $/* range -2..-2 */

crates/tinymist-query/src/fixtures/code_action/equation_block5.typ

@@ -0,0 +1 @@
+$ a $/* range -4..-4 */

crates/tinymist-query/src/fixtures/code_action/equation_block6.typ

@@ -0,0 +1 @@
+$ a $/* range -5..-5 */

crates/tinymist-query/src/fixtures/code_action/equation_block_multiline.typ

@@ -0,0 +1,3 @@
+$
+a
+$/* range -1..-1 */

crates/tinymist-query/src/fixtures/code_action/equation_block_multiline_empty.typ

@@ -0,0 +1,2 @@
+$
+$/* range -1..-1 */

crates/tinymist-query/src/fixtures/code_action/equation_block_punctuation.typ

@@ -0,0 +1 @@
+$ a $. /* range -4..-4 */