biomejs · dyc3 · Feb 20, 2026 · Feb 20, 2026 · Feb 20, 2026
diff --git a/.changeset/no-assign-in-expressions-vue-v-on.md b/.changeset/no-assign-in-expressions-vue-v-on.md
@@ -0,0 +1,5 @@
+---
+"@biomejs/biome": patch
+---
+
+Fixed [#9161](https://github.com/biomejs/biome/issues/9161): The `noAssignInExpressions` rule no longer flags assignments in Vue v-on directives (e.g., `@click="counter += 1"`). Assignments in event handlers are idiomatic Vue patterns and are now skipped by the rule.
diff --git a/crates/biome_cli/tests/cases/handle_vue_files.rs b/crates/biome_cli/tests/cases/handle_vue_files.rs
@@ -1614,3 +1614,76 @@ fn no_comma_operator_not_triggered_in_v_for() {
         result,
     ));
 }
+
+#[test]
+fn no_assign_in_expressions_not_triggered_in_v_on() {
+    let fs = MemoryFileSystem::default();
+    let mut console = BufferConsole::default();
+    fs.insert(
+        "biome.json".into(),
+        r#"{ "html": { "linter": {"enabled": true}, "experimentalFullSupportEnabled": true } }"#
+            .as_bytes(),
+    );
+    let file = Utf8Path::new("file.vue");
+    fs.insert(
+        file.into(),
+        r#"<script setup>
+let counter = 0;
+</script>
+<template>
+  <!-- shorthand @click -->
+  <button type="button" @click="counter += 1">+</button>
+  <!-- longhand v-on:click -->
+  <button type="button" v-on:click="counter -= 1">-</button>
+</template>"#
+            .as_bytes(),
+    );
+    let (fs, result) = run_cli(
+        fs,
+        &mut console,
+        Args::from(["lint", "--only=noAssignInExpressions", file.as_str()].as_slice()),
+    );
+    assert!(result.is_ok(), "run_cli returned {result:?}");
+    assert_cli_snapshot(SnapshotPayload::new(
+        module_path!(),
+        "no_assign_in_expressions_not_triggered_in_v_on",
+        fs,
+        console,
+        result,
+    ));
+}
+
+#[test]
+fn no_assign_in_expressions_triggered_in_template_interpolation() {
+    let fs = MemoryFileSystem::default();
+    let mut console = BufferConsole::default();
+    fs.insert(
+        "biome.json".into(),
+        r#"{ "html": { "linter": {"enabled": true}, "experimentalFullSupportEnabled": true } }"#
+            .as_bytes(),
+    );
+    let file = Utf8Path::new("file.vue");
+    fs.insert(
+        file.into(),
+        r#"<script setup>
+let counter = 0;
+</script>
+<template>
+  <p>{{ counter += 1 }}</p>
+</template>"#
+            .as_bytes(),
+    );
+    let (fs, result) = run_cli(
+        fs,
+        &mut console,
+        Args::from(["lint", "--only=noAssignInExpressions", file.as_str()].as_slice()),
+    );
+    assert!(result.is_err(), "run_cli returned {result:?}");
+    assert_cli_snapshot(SnapshotPayload::new(
+        module_path!(),
+        "no_assign_in_expressions_triggered_in_template_interpolation",
+        fs,
+        console,
+        result,
+    ));
+}
diff --git a/...snapshots/main_cases_handle_vue_files/no_assign_in_expressions_not_triggered_in_v_on.snap b/...snapshots/main_cases_handle_vue_files/no_assign_in_expressions_not_triggered_in_v_on.snap
@@ -0,0 +1,34 @@
+---
+source: crates/biome_cli/tests/snap_test.rs
+expression: redactor(content)
+---
+## `biome.json`
+
+```json
+{
+  "html": {
+    "linter": { "enabled": true },
+    "experimentalFullSupportEnabled": true
+  }
+}
+```
+
+## `file.vue`
+
+```vue
+<script setup>
+let counter = 0;
+</script>
+<template>
+  <!-- shorthand @click -->
+  <button type="button" @click="counter += 1">+</button>
+  <!-- longhand v-on:click -->
+  <button type="button" v-on:click="counter -= 1">-</button>
+</template>
+```
+
+# Emitted Messages
+
+```block
+Checked 1 file in <TIME>. No fixes applied.
+```
diff --git a/..._cases_handle_vue_files/no_assign_in_expressions_triggered_in_template_interpolation.snap b/..._cases_handle_vue_files/no_assign_in_expressions_triggered_in_template_interpolation.snap
@@ -0,0 +1,60 @@
+---
+source: crates/biome_cli/tests/snap_test.rs
+expression: redactor(content)
+---
+## `biome.json`
+
+```json
+{
+  "html": {
+    "linter": { "enabled": true },
+    "experimentalFullSupportEnabled": true
+  }
+}
+```
+
+## `file.vue`
+
+```vue
+<script setup>
+let counter = 0;
+</script>
+<template>
+  <p>{{ counter += 1 }}</p>
+</template>
+```
+
+# Termination Message
+
+```block
+lint ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  × Some errors were emitted while running checks.
+
+
+
+```
+
+# Emitted Messages
+
+```block
+file.vue:5:9 lint/suspicious/noAssignInExpressions ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+
+  × The assignment should not be in an expression.
+
+    3 │ </script>
+    4 │ <template>
+  > 5 │   <p>{{ counter += 1 }}</p>
+      │         ^^^^^^^^^^^^
+    6 │ </template>
+
+  i The use of assignments in expressions is confusing.
+    Expressions are often considered as side-effect free.
+
+
+```
+
+```block
+Checked 1 file in <TIME>. No fixes applied.
+Found 1 error.
+```
diff --git a/crates/biome_js_analyze/src/lint/suspicious/no_assign_in_expressions.rs b/crates/biome_js_analyze/src/lint/suspicious/no_assign_in_expressions.rs
@@ -4,7 +4,7 @@ use biome_console::markup;
 use biome_diagnostics::Severity;
 use biome_js_syntax::{
     AnyJsFunctionBody, JsArrowFunctionExpression, JsAssignmentExpression, JsExpressionStatement,
-    JsForStatement, JsParenthesizedExpression, JsSequenceExpression,
+    JsFileSource, JsForStatement, JsParenthesizedExpression, JsSequenceExpression,
 };
 use biome_rowan::AstNode;
 use biome_rule_options::no_assign_in_expressions::NoAssignInExpressionsOptions;
@@ -65,6 +65,13 @@ impl Rule for NoAssignInExpressions {
     type Options = NoAssignInExpressionsOptions;
 
     fn run(ctx: &RuleContext<Self>) -> Self::Signals {
+        // Skip assignments in Vue event handlers (v-on directives)
+        // These are idiomatic Vue patterns, not accidental assignments
+        let file_source = ctx.source_type::<JsFileSource>();
+        if file_source.is_vue_event_handler() {
+            return None;
+        }
+
         let assign = ctx.query();
         let mut ancestor = assign
             .syntax()

diff --git a/crates/biome_js_syntax/src/file_source.rs b/crates/biome_js_syntax/src/file_source.rs
@@ -129,6 +129,8 @@ pub enum EmbeddingKind {
         setup: bool,
         /// Where the bindings are defined
         is_source: bool,
+        /// Whether this is a v-on event handler (e.g., @click="handler")
+        event_handler: bool,
     },
     Svelte {
         /// Where the bindings are defined
@@ -151,6 +153,15 @@ impl EmbeddingKind {
     pub const fn is_vue_setup(&self) -> bool {
         matches!(self, Self::Vue { setup: true, .. })
     }
+    pub const fn is_vue_event_handler(&self) -> bool {
+        matches!(
+            self,
+            Self::Vue {
+                event_handler: true,
+                ..
+            }
+        )
+    }
     pub const fn is_svelte(&self) -> bool {
         matches!(self, Self::Svelte { .. })
     }
@@ -226,6 +237,7 @@ impl JsFileSource {
         Self::js_module().with_embedding_kind(EmbeddingKind::Vue {
             setup: false,
             is_source: true,
+            event_handler: false,
         })
     }
 
@@ -234,6 +246,7 @@ impl JsFileSource {
         Self::js_module().with_embedding_kind(EmbeddingKind::Vue {
             setup: true,
             is_source: true,
+            event_handler: false,
         })
     }
 
@@ -338,6 +351,11 @@ impl JsFileSource {
         )
     }
 
+    /// Returns true if this is a Vue event handler (v-on directive)
+    pub const fn is_vue_event_handler(&self) -> bool {
+        self.embedding_kind.is_vue_event_handler()
+    }
+
     pub const fn as_embedding_kind(&self) -> &EmbeddingKind {
         &self.embedding_kind
     }

diff --git a/crates/biome_service/src/file_handlers/html.rs b/crates/biome_service/src/file_handlers/html.rs
@@ -627,6 +627,7 @@ fn parse_embedded_nodes(
                         embedded_file_source.with_embedding_kind(EmbeddingKind::Vue {
                             setup: false,
                             is_source: false,
+                            event_handler: true,
                         });
                     if let Some((content, doc_source)) = parse_directive_string_value(
                         &initializer,
@@ -647,6 +648,7 @@ fn parse_embedded_nodes(
                         embedded_file_source.with_embedding_kind(EmbeddingKind::Vue {
                             setup: false,
                             is_source: false,
+                            event_handler: false,
                         });
                     if let Some((content, doc_source)) = parse_directive_string_value(
                         &initializer,
@@ -667,6 +669,7 @@ fn parse_embedded_nodes(
                         embedded_file_source.with_embedding_kind(EmbeddingKind::Vue {
                             setup: false,
                             is_source: false,
+                            event_handler: false,
                         });
                     if let Some((content, doc_source)) = parse_directive_string_value(
                         &initializer,
@@ -683,10 +686,15 @@ fn parse_embedded_nodes(
                 if let Some(directive) = VueDirective::cast_ref(&element)
                     && let Some(initializer) = directive.initializer()
                 {
+                    let is_v_on = directive
+                        .name_token()
+                        .map(|t| t.text_trimmed() == "v-on")
+                        .unwrap_or(false);
                     let file_source =
                         embedded_file_source.with_embedding_kind(EmbeddingKind::Vue {
                             setup: false,
                             is_source: false,
+                            event_handler: is_v_on,
                         });
                     if let Some((content, doc_source)) = parse_directive_string_value(
                         &initializer,
@@ -934,6 +942,7 @@ pub(crate) fn parse_embedded_script(
                 file_source = file_source.with_embedding_kind(EmbeddingKind::Vue {
                     setup: element.is_script_with_setup_attribute(),
                     is_source: true,
+                    event_handler: false,
                 });
             }
             file_source
@@ -1195,6 +1204,7 @@ pub(crate) fn parse_vue_text_expression(
     let file_source = js_file_source.with_embedding_kind(EmbeddingKind::Vue {
         setup: false,
         is_source: false,
+        event_handler: false,
     });
     parse_text_expression(expression, cache, biome_path, settings, file_source)
 }

diff --git a/crates/biome_service/src/file_handlers/vue.rs b/crates/biome_service/src/file_handlers/vue.rs
@@ -81,6 +81,7 @@ impl VueFileHandler {
                         .with_embedding_kind(EmbeddingKind::Vue {
                             setup,
                             is_source: true,
+                            event_handler: false,
                         }),
                 )
             })

diff --git a/packages/@biomejs/backend-jsonrpc/src/workspace.ts b/packages/@biomejs/backend-jsonrpc/src/workspace.ts
-Original file line number
+Diff line change
@@ Expand Up / @@ -81,6 +81,7 @@ impl VueFileHandler { @@
                             .with_embedding_kind(EmbeddingKind::Vue {
                                 setup,
                                 is_source: true,
+                                event_handler: false,
                             }),
                     )
                 })
@@ Expand Down @@