[lang] remove EnvAccess inherent emit_event to avoid override (#378)

* Rename EnvAccess direct emit_event method to avoid override

* Remove EmitEvent trait import

* Add test for decoding Transfer Event

* Only provide test Event alias when there are events

* Fmt

* Revert "Remove EmitEvent trait import"

This reverts commit 078fb09f

* Rename emit_event_inner to emit_event_generic

* Be more explicit calling emit_event

* Be more explicit calling emit_event

* Rename to emit_generic_event

* Remove EnvAccess method entirely

examples/erc20/src/lib.rs

@@ -155,8 +155,18 @@ mod erc20 {
         fn new_works() {
             // Constructor works.
             let _erc20 = Erc20::new(100);
+
             // Transfer event triggered during initial contruction.
-            assert_eq!(1, env::test::recorded_events().count());
+            let emitted_events = env::test::recorded_events().collect::<Vec<_>>();
+            assert_eq!(1, emitted_events.len());
+            let raw_event = emitted_events.first().unwrap();
+            let event = <Event as scale::Decode>::decode(&mut &raw_event.data[..])
+                .expect("Invalid contract Event");
+            if let Event::Transfer(transfer) = event {
+                assert_eq!(100, transfer.value);
+            } else {
+                panic!("Expected a Transfer Event")
+            }
         }
 
         /// The total supply was applied.

lang/macro/src/codegen/contract.rs

@@ -69,6 +69,15 @@ impl GenerateCode for ContractModule<'_> {
         let cross_calling = self.generate_code_using::<CrossCalling>();
         let non_ink_items = &self.contract.non_ink_items;
 
+        let test_event_alias = if !self.contract.events.is_empty() {
+            quote! {
+                #[cfg(all(test, feature = "test-env"))]
+                pub type Event = self::__ink_private::Event;
+            }
+        } else {
+            quote! {}
+        };
+
         quote! {
             mod #ident {
                 #env_types
@@ -96,6 +105,8 @@ impl GenerateCode for ContractModule<'_> {
                 #[cfg(feature = "ink-as-dependency")]
                 pub type #storage_ident = self::__ink_private::StorageAsDependency;
 
+                #test_event_alias
+
                 #event_structs
 
                 #(

lang/macro/src/codegen/events.rs

@@ -119,7 +119,7 @@ impl EventHelpers<'_> {
                     where
                         E: Into<Self::Event>,
                     {
-                        ink_lang::EnvAccess::<EnvTypes>::emit_event(self, event.into())
+                        ink_core::env::emit_event::<EnvTypes, Self::Event>(event.into());
                     }
                 }
             };
@@ -135,7 +135,7 @@ impl EventHelpers<'_> {
             .collect::<Vec<_>>();
 
         quote! {
-            #[derive(scale::Encode)]
+            #[derive(scale::Encode, scale::Decode)]
             pub enum Event {
                 #( #event_idents(#event_idents), )*
             }
@@ -182,7 +182,7 @@ impl EventHelpers<'_> {
 ///
 /// - making all fields `pub`
 /// - strip `#[ink(..)]` attributes
-/// - add `#[derive(scale::Encode)]`
+/// - add `#[derive(scale::Encode, scale::Decode)]`
 ///
 /// # Note
 ///
@@ -223,7 +223,7 @@ impl EventStructs<'_> {
             quote_spanned!(span =>
                 #conflic_depedency_cfg
                 #(#attrs)*
-                #[derive(scale::Encode)]
+                #[derive(scale::Encode, scale::Decode)]
                 pub struct #ident
                     #fields
             )

lang/src/env_access.rs

@@ -23,7 +23,6 @@ use ink_core::{
         },
         EnvTypes,
         Result,
-        Topics,
     },
 };
 use ink_primitives::Key;
@@ -185,18 +184,6 @@ where
         env::tombstone_deposit::<T>().expect("couldn't decode tombstone deposits")
     }
 
-    /// Emits an event with the given event data.
-    ///
-    /// # Note
-    ///
-    /// For more details visit: [`ink_core::env::emit_event`]
-    pub fn emit_event<Event>(self, event: Event)
-    where
-        Event: Topics<T> + scale::Encode,
-    {
-        env::emit_event::<T, Event>(event)
-    }
-
     /// Sets the rent allowance of the executed contract to the new value.
     ///
     /// # Note