From d9916fcc9c4eb55ff746d5e742068cfbbacb0199 Mon Sep 17 00:00:00 2001
From: 54k1 <59379616+54k1@users.noreply.github.com>
Date: Sat, 9 Jan 2021 00:17:59 +0530
Subject: [PATCH] Modify environment binding behaviour of function (#1010)

* Modify environment binding behaviour of function

* Add basic test
---
 .../ast/node/declaration/function_decl/mod.rs | 25 +++++++++++--------
 boa/src/syntax/ast/node/declaration/mod.rs    |  3 +++
 boa/src/syntax/ast/node/declaration/tests.rs  | 12 +++++++++
 3 files changed, 30 insertions(+), 10 deletions(-)
 create mode 100644 boa/src/syntax/ast/node/declaration/tests.rs

diff --git a/boa/src/syntax/ast/node/declaration/function_decl/mod.rs b/boa/src/syntax/ast/node/declaration/function_decl/mod.rs
index 9309ce2e1e..999faebdd4 100644
--- a/boa/src/syntax/ast/node/declaration/function_decl/mod.rs
+++ b/boa/src/syntax/ast/node/declaration/function_decl/mod.rs
@@ -94,18 +94,23 @@ impl Executable for FunctionDecl {
 
         // Set the name and assign it in the current environment
         val.set_field("name", self.name(), context)?;
-        context
-            .realm_mut()
-            .environment
-            .create_mutable_binding(self.name().to_owned(), false, VariableScope::Function)
-            .map_err(|e| e.to_error(context))?;
 
-        context
-            .realm_mut()
-            .environment
-            .initialize_binding(self.name(), val)
-            .map_err(|e| e.to_error(context))?;
+        let environment = &mut context.realm_mut().environment;
+        if environment.has_binding(self.name()) {
+            environment
+                .set_mutable_binding(self.name(), val, true)
+                .map_err(|e| e.to_error(context))?;
+        } else {
+            environment
+                .create_mutable_binding(self.name().to_owned(), false, VariableScope::Function)
+                .map_err(|e| e.to_error(context))?;
 
+            context
+                .realm_mut()
+                .environment
+                .initialize_binding(self.name(), val)
+                .map_err(|e| e.to_error(context))?;
+        }
         Ok(Value::undefined())
     }
 }
diff --git a/boa/src/syntax/ast/node/declaration/mod.rs b/boa/src/syntax/ast/node/declaration/mod.rs
index a256a75e87..ac5a0dbbb9 100644
--- a/boa/src/syntax/ast/node/declaration/mod.rs
+++ b/boa/src/syntax/ast/node/declaration/mod.rs
@@ -19,3 +19,6 @@ pub use self::{
     let_decl_list::{LetDecl, LetDeclList},
     var_decl_list::{VarDecl, VarDeclList},
 };
+
+#[cfg(test)]
+mod tests;
diff --git a/boa/src/syntax/ast/node/declaration/tests.rs b/boa/src/syntax/ast/node/declaration/tests.rs
new file mode 100644
index 0000000000..a98ac86f52
--- /dev/null
+++ b/boa/src/syntax/ast/node/declaration/tests.rs
@@ -0,0 +1,12 @@
+use crate::exec;
+
+#[test]
+fn duplicate_function_name() {
+    let scenario = r#"
+    function f () {}
+    function f () {return 12;}
+    f()
+    "#;
+
+    assert_eq!(&exec(scenario), "12");
+}