From 06e72461bd445d4ed662836638701e14fe2878a6 Mon Sep 17 00:00:00 2001
From: Victorien Elvinger <victorien@elvinger.fr>
Date: Mon, 30 Sep 2024 18:03:11 +0200
Subject: [PATCH] fix(noUnusedVariables): don't panic when renaming ref at the
 start

---
 CHANGELOG.md                                  |  2 ++
 .../noUnusedVariables/issue4114.js            |  2 ++
 .../noUnusedVariables/issue4114.js.snap       | 31 +++++++++++++++++++
 .../src/semantic_model/model.rs               |  5 ++-
 .../src/semantic_model/reference.rs           |  8 +++--
 5 files changed, 44 insertions(+), 4 deletions(-)
 create mode 100644 crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js
 create mode 100644 crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js.snap

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 10b3283d1cc7..de1864582c7b 100644
--- a/CHANGELOG.md
+++ b/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
diff --git a/crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js b/crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js
new file mode 100644
index 000000000000..963a7b32417a
--- /dev/null
+++ b/crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js
@@ -0,0 +1,2 @@
+c;
+const c = 0;
\ No newline at end of file
diff --git a/crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js.snap b/crates/biome_js_analyze/tests/specs/correctness/noUnusedVariables/issue4114.js.snap
new file mode 100644
index 000000000000..bc22f1dfa9a8
--- /dev/null
+++ b/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;
+  
+
+```
diff --git a/crates/biome_js_semantic/src/semantic_model/model.rs b/crates/biome_js_semantic/src/semantic_model/model.rs
index 436aad7771f4..97e34d49bb11 100644
--- a/crates/biome_js_semantic/src/semantic_model/model.rs
+++ b/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,
diff --git a/crates/biome_js_semantic/src/semantic_model/reference.rs b/crates/biome_js_semantic/src/semantic_model/reference.rs
index 105d89813584..8d53e8497bbb 100644
--- a/crates/biome_js_semantic/src/semantic_model/reference.rs
+++ b/crates/biome_js_semantic/src/semantic_model/reference.rs
@@ -58,9 +58,11 @@ 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,
+            start.checked_add(1.into()).unwrap_or(start),
+        ));
         Scope {
             data: self.data.clone(),
             id,