biomejs · harshasiddartha · Oct 31, 2025 · Nov 1, 2025 · Nov 1, 2025 · Nov 3, 2025
diff --git a/.changeset/no-extra-non-null-assertion-compound-assign.md b/.changeset/no-extra-non-null-assertion-compound-assign.md
@@ -0,0 +1,22 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#7927](https://github.com/biomejs/biome/issues/7927): [`noExtraNonNullAssertion`](https://biomejs.dev/linter/rules/no-extra-non-null-assertion) incorrectly flagged separate non-null assertions on both sides of an assignment.
+
+The rule now correctly distinguishes between nested non-null assertions (still flagged) and separate non-null assertions on different sides of an assignment (allowed).
+
+#### Examples
+
+##### Valid (now allowed)
+
+```ts
+arr[0]! ^= arr[1]!;
+```
+
+##### Invalid (still flagged)
+
+```ts
+arr[0]!! ^= arr[1];
+arr[0] ^= arr[1]!!;
+```
diff --git a/crates/biome_js_analyze/src/lint/suspicious/no_extra_non_null_assertion.rs b/crates/biome_js_analyze/src/lint/suspicious/no_extra_non_null_assertion.rs
@@ -82,6 +82,27 @@ impl Rule for NoExtraNonNullAssertion {
                 }
             }
             AnyTsNonNullAssertion::TsNonNullAssertionExpression(_) => {
+                // First check if this is nested within another non-null assertion (always invalid)
+                let is_nested_in_non_null_assertion = node
+                    .syntax()
+                    .ancestors()
+                    .skip(1)
+                    .find_map(|ancestor| {
+                        if ancestor.kind() == JsSyntaxKind::TS_NON_NULL_ASSERTION_EXPRESSION {
+                            Some(true)
+                        } else if ancestor.kind() == JsSyntaxKind::JS_PARENTHESIZED_EXPRESSION {
+                            None // Continue searching
+                        } else {
+                            Some(false) // Found a different ancestor, stop searching
+                        }
+                    })
+                    .unwrap_or(false);
+
+                if is_nested_in_non_null_assertion {
+                    return Some(());
+                }
+
+                // Then check other cases
                 let parent = node
                     .syntax()
                     .ancestors()
@@ -90,17 +111,31 @@ impl Rule for NoExtraNonNullAssertion {
                     .and_then(AnyJsExpression::cast)?;
 
                 // Cases considered as invalid:
-                // - TsNonNullAssertionAssignment > TsNonNullAssertionExpression
-                // - TsNonNullAssertionExpression > TsNonNullAssertionExpression
+                // - TsNonNullAssertionAssignment > TsNonNullAssertionExpression (nested in left side)
                 // - JsCallExpression[optional] > TsNonNullAssertionExpression
                 // - JsStaticMemberExpression[optional] > TsNonNullAssertionExpression
                 let has_extra_non_assertion = match parent {
-                    AnyJsExpression::JsAssignmentExpression(expr) => expr
-                        .left()
-                        .ok()?
-                        .as_any_js_assignment()?
-                        .as_ts_non_null_assertion_assignment()
-                        .is_some(),
+                    AnyJsExpression::JsAssignmentExpression(expr) => {
+                        // Only flag if the non-null assertion is nested within the left side,
+                        // not if it's a separate assertion on the right side
+                        let left = expr.left().ok()?;
+                        let left_syntax = left.syntax();
+                        let current_syntax = node.syntax();
+
+                        // Check if current node is nested within the left side
+                        if left_syntax
+                            .descendants()
+                            .any(|desc| desc == *current_syntax)
+                        {
+                            left.as_any_js_assignment()?
+                                .as_ts_non_null_assertion_assignment()
+                                .is_some()
+                        } else {
+                            // Current node is on the right side, don't flag it
+                            // (nested assertions on right side are already handled above)
+                            false
+                        }
+                    }
                     AnyJsExpression::TsNonNullAssertionExpression(_) => true,
                     AnyJsExpression::JsStaticMemberExpression(expr) => expr.is_optional(),
                     AnyJsExpression::JsCallExpression(expr) => expr.is_optional(),

diff --git a/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/invalid.ts b/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/invalid.ts
@@ -46,3 +46,10 @@ case14!! = null
 if (case15!!) {}
 
 if (!case16!!) {}
+
+// Test cases for issue #7927: nested assertions in compound assignments should be flagged
+const arr1: number[] = [1, 2, 3];
+arr1[0]!! ^= arr1[1];
+
+const arr2: number[] = [1, 2, 3];
+arr2[0] ^= arr2[1]!!;
diff --git a/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/invalid.ts.snap b/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/invalid.ts.snap
@@ -1,5 +1,6 @@
 ---
 source: crates/biome_js_analyze/tests/spec_tests.rs
+assertion_line: 151
 expression: invalid.ts
 ---
 # Input
@@ -53,6 +54,13 @@ if (case15!!) {}
 
 if (!case16!!) {}
 
+// Test cases for issue #7927: nested assertions in compound assignments should be flagged
+const arr1: number[] = [1, 2, 3];
+arr1[0]!! ^= arr1[1];
+
+const arr2: number[] = [1, 2, 3];
+arr2[0] ^= arr2[1]!!;
+
 ```
 
 # Diagnostics
@@ -284,14 +292,14 @@ invalid.ts:42:1 lint/suspicious/noExtraNonNullAssertion  FIXABLE  ━━━━
     40 │ case12!?.[a.b!!];
     41 │ 
   > 42 │ case13!!! = null
-       │ ^^^^^^^^
+       │ ^^^^^^^
     43 │ 
     44 │ case14!! = null
 
   i Safe fix: Remove extra non-null assertion.
 
     42 │ case13!!!·=·null
-       │        -        
+       │       -         
 
 ```
 
@@ -303,14 +311,14 @@ invalid.ts:42:1 lint/suspicious/noExtraNonNullAssertion  FIXABLE  ━━━━
     40 │ case12!?.[a.b!!];
     41 │ 
   > 42 │ case13!!! = null
-       │ ^^^^^^^
+       │ ^^^^^^^^
     43 │ 
     44 │ case14!! = null
 
   i Safe fix: Remove extra non-null assertion.
 
     42 │ case13!!!·=·null
-       │       -         
+       │        -        
 
 ```
 
@@ -362,10 +370,47 @@ invalid.ts:48:6 lint/suspicious/noExtraNonNullAssertion  FIXABLE  ━━━━
   > 48 │ if (!case16!!) {}
        │      ^^^^^^^
     49 │ 
+    50 │ // Test cases for issue #7927: nested assertions in compound assignments should be flagged
 
   i Safe fix: Remove extra non-null assertion.
 
     48 │ if·(!case16!!)·{}
        │            -     
 
 ```
+
+```
+invalid.ts:52:1 lint/suspicious/noExtraNonNullAssertion  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! Forbidden extra non-null assertion.
+
+    50 │ // Test cases for issue #7927: nested assertions in compound assignments should be flagged
+    51 │ const arr1: number[] = [1, 2, 3];
+  > 52 │ arr1[0]!! ^= arr1[1];
+       │ ^^^^^^^^
+    53 │ 
+    54 │ const arr2: number[] = [1, 2, 3];
+
+  i Safe fix: Remove extra non-null assertion.
+
+    52 │ arr1[0]!!·^=·arr1[1];
+       │        -             
+
+```
+
+```
+invalid.ts:55:12 lint/suspicious/noExtraNonNullAssertion  FIXABLE  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  ! Forbidden extra non-null assertion.
+
+    54 │ const arr2: number[] = [1, 2, 3];
+  > 55 │ arr2[0] ^= arr2[1]!!;
+       │            ^^^^^^^^
+    56 │ 
+
+  i Safe fix: Remove extra non-null assertion.
+
+    55 │ arr2[0]·^=·arr2[1]!!;
+       │                   -  
+
+```
diff --git a/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/valid.ts b/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/valid.ts
@@ -19,3 +19,7 @@ function case5(key: string | null) {
 function issue3419(value: string | null): string {
   return (value!);
 }
+
+// Test case for issue #7927: compound assignment with non-null assertions on both sides
+const arr: number[] = [1, 2, 3];
+arr[0]! ^= arr[1]!;
diff --git a/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/valid.ts.snap b/crates/biome_js_analyze/tests/specs/suspicious/noExtraNonNullAssertion/valid.ts.snap
@@ -1,5 +1,6 @@
 ---
 source: crates/biome_js_analyze/tests/spec_tests.rs
+assertion_line: 151
 expression: valid.ts
 ---
 # Input
@@ -26,4 +27,8 @@ function issue3419(value: string | null): string {
   return (value!);
 }
 
+// Test case for issue #7927: compound assignment with non-null assertions on both sides
+const arr: number[] = [1, 2, 3];
+arr[0]! ^= arr[1]!;
+
 ```