fix(noUnusedVariables): don't panic when renaming ref at the start

CHANGELOG.md

@@ -105,6 +105,8 @@ our [guidelines for writing a good changelog entry](https://github.com/biomejs/b
 
   Contributed by @Conaclos
 
+- [noUnusedVariables](https://biomejs.dev/linter/rules/no-unused-variables/) no longer panics when suggesting the renaming of a variable at the start of a file ([#4114](https://github.com/biomejs/biome/issues/4114)). Contributed by @Conaclos
+
 - [noUselessEscapeInRegex](https://biomejs.dev/linter/rules/no-useless-escape-in-regex/) no longer panics on regexes that start with an empty character class. Contributed by @Conaclos
 
 - [noUselessStringConcat](https://biomejs.dev/linter/rules/no-useless-string-concat/) no longer panics when it encounters malformed code. Contributed by @Conaclos

crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js

@@ -0,0 +1,2 @@
+c;
+const c = 0;

crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js.snap

@@ -0,0 +1,31 @@
+---
+source: crates/biome_js_analyze/tests/spec_tests.rs
+expression: issue4114.js
+---
+# Input
+```jsx
+c;
+const c = 0;
+```
+
+# Diagnostics
+```
+issue4114.js:2:7 lint/correctness/noUnusedVariables  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! This variable is unused.
+
+    1 │ c;
+  > 2 │ const c = 0;
+      │       ^
+
+  i Unused variables usually are result of incomplete refactoring, typos and other source of bugs.
+
+  i Unsafe fix: If this is intentional, prepend c with an underscore.
+
+    1   │ - c;
+    2   │ - const·c·=·0;
+      1 │ + _c;
+      2 │ + const·_c·=·0;
+
+
+```

crates/biome_js_semantic/src/semantic_model/model.rs

@@ -124,13 +124,16 @@ impl SemanticModelData {
 
     /// Returns the [ScopeId] which the syntax is part of.
     pub(crate) fn scope(&self, range: TextRange) -> ScopeId {
+        // Seeking an interval in `self.scope_by_range` require a non-empty interval
+        debug_assert!(range.len() > 0.into(), "the range must not be empty.");
         let start = range.start().into();
         let end = range.end().into();
         let scopes = self
             .scope_by_range
+            // Find overlapping intervals
             .find(start, end)
+            // Only take intersecting intervals
             .filter(|x| !(start < x.start || end > x.stop));
-
         // We always want the most tight scope
         match scopes.map(|x| x.val).max() {
             Some(val) => val,

crates/biome_js_semantic/src/semantic_model/reference.rs

@@ -58,9 +58,12 @@ impl Reference {
 
     /// Returns the scope of this reference
     pub fn scope(&self) -> Scope {
-        let id = self
-            .data
-            .scope(TextRange::new(self.range_start(), self.range_start()));
+        let start = self.range_start();
+        let id = self.data.scope(TextRange::new(
+            start,
+            // SAFETY: A reference name has at least a length of 1 byte.
+            start + TextSize::from(1),
+        ));
         Scope {
             data: self.data.clone(),
             id,