Fix crashing on empty regexps (#1870)

crates/typst/src/model/selector.rs

@@ -40,8 +40,22 @@ pub enum Selector {
 
 impl Selector {
     /// Define a simple text selector.
-    pub fn text(text: &str) -> Self {
-        Self::Regex(Regex::new(&regex::escape(text)).unwrap())
+    pub fn text(text: &str) -> StrResult<Self> {
+        if text.is_empty() {
+            bail!("text selector is empty");
+        }
+        Ok(Self::Regex(Regex::new(&regex::escape(text)).unwrap()))
+    }
+
+    /// Define a regex selector.
+    pub fn regex(regex: Regex) -> StrResult<Self> {
+        if regex.as_str().is_empty() {
+            bail!("regex selector is empty");
+        }
+        if regex.is_match("") {
+            bail!("regex matches empty text");
+        }
+        Ok(Self::Regex(regex))
     }
 
     /// Define a simple [`Selector::Can`] selector.
@@ -158,8 +172,8 @@ cast! {
         .ok_or("only element functions can be used as selectors")?
         .select(),
     label: Label => Self::Label(label),
-    text: EcoString => Self::text(&text),
-    regex: Regex => Self::Regex(regex),
+    text: EcoString => Self::text(&text)?,
+    regex: Regex => Self::regex(regex)?,
     location: Location => Self::Location(location),
 }
 

tests/typ/compiler/show-text.typ

@@ -25,6 +25,19 @@ AA (8)
 
 Treeworld, the World of worlds, is a world.
 
+---
+// Test there is no crashing on empty strings
+// Error: 1:7-1:9 text selector is empty
+#show "": []
+
+---
+// Error: 1:7-1:16 regex selector is empty
+#show regex(""): [AA]
+
+---
+// Error: 1:7-1:42 regex matches empty text
+#show regex("(VAR_GLOBAL|END_VAR||BOOL)") : []
+
 ---
 // This is a fun one.
 #set par(justify: true)