Check for unnecessary visibility qualifier in trait items. (FuelLabs#…

…2276)

This introduces a new check for unnecessary visibility qualifiers
when defining trait items.

For code like:

```
trait A {} {
    pub fn f(self) -> bool {
        false
    }
}
```

We now emit:

```
error
 --> main.sw:4:5
  |
2 |
3 | trait A {} {
4 |     pub fn f(self) -> bool {
  |     ^^^ Unnecessary visibility qualifier.
5 |         false
6 |     }
  |
____
```

Also adds some tests for both trait interface and method blocks.

Co-authored-by: Mohammad Fawaz <[email protected]>

sway-lib-std/src/u128.sw

@@ -18,7 +18,7 @@ pub enum U128Error {
 
 pub trait From {
     /// Function for creating U128 from its u64 components.
-    pub fn from(upper: u64, lower: u64) -> Self;
+    fn from(upper: u64, lower: u64) -> Self;
     fn into(self) -> (u64, u64);
 }
 

sway-lib-std/src/u256.sw

@@ -18,7 +18,7 @@ pub enum U256Error {
 
 pub trait From {
     /// Function for creating a U256 from its u64 components.
-    pub fn from(a: u64, b: u64, c: u64, d: u64) -> Self;
+    fn from(a: u64, b: u64, c: u64, d: u64) -> Self;
     fn into(self) -> (u64, u64, u64, u64);
 }
 

sway-parse/src/error.rs

@@ -68,6 +68,8 @@ pub enum ParseErrorKind {
     UnexpectedRestPattern,
     #[error("Identifiers cannot be a reserved keyword.")]
     ReservedKeywordIdentifier,
+    #[error("Unnecessary visibility qualifier, `{}` is implied here.", visibility)]
+    UnnecessaryVisibilityQualifier { visibility: Ident },
 }
 
 #[derive(Debug, Error, Clone, PartialEq, Hash)]

sway-parse/src/item/item_trait.rs

@@ -42,8 +42,34 @@ impl Parse for ItemTrait {
             }
             None => None,
         };
-        let trait_items = parser.parse()?;
-        let trait_defs_opt = Braces::try_parse(parser)?;
+
+        let trait_items: Braces<Vec<(Annotated<FnSignature>, _)>> = parser.parse()?;
+        for item in trait_items.get().iter() {
+            let (fn_sig, _) = item;
+            if let Some(token) = &fn_sig.value.visibility {
+                return Err(parser.emit_error_with_span(
+                    ParseErrorKind::UnnecessaryVisibilityQualifier {
+                        visibility: token.ident(),
+                    },
+                    token.span(),
+                ));
+            }
+        }
+
+        let trait_defs_opt: Option<Braces<Vec<Annotated<ItemFn>>>> = Braces::try_parse(parser)?;
+        if let Some(trait_defs) = &trait_defs_opt {
+            for item in trait_defs.get().iter() {
+                if let Some(token) = &item.value.fn_signature.visibility {
+                    return Err(parser.emit_error_with_span(
+                        ParseErrorKind::UnnecessaryVisibilityQualifier {
+                            visibility: token.ident(),
+                        },
+                        token.span(),
+                    ));
+                }
+            }
+        }
+
         Ok(ItemTrait {
             visibility,
             trait_token,

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_interface/Forc.lock

@@ -0,0 +1,4 @@
+[[package]]
+name = 'trait_pub_fn_interface'
+source = 'root'
+dependencies = []

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_interface/Forc.toml

@@ -0,0 +1,6 @@
+[project]
+name = "trait_pub_fn_interface"
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+implicit-std = false

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_interface/src/main.sw

@@ -0,0 +1,5 @@
+contract;
+
+trait A {
+    pub fn f(self) -> bool;
+}

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_interface/test.toml

@@ -0,0 +1,4 @@
+category = "fail"
+
+# check: pub fn f(self) -> bool;
+# nextln: $()Unnecessary visibility qualifier, `pub` is implied here.

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_method/Forc.lock

@@ -0,0 +1,4 @@
+[[package]]
+name = 'trait_pub_fn_method'
+source = 'root'
+dependencies = []

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_method/Forc.toml

@@ -0,0 +1,6 @@
+[project]
+name = "trait_pub_fn_method"
+authors = ["Fuel Labs <[email protected]>"]
+entry = "main.sw"
+license = "Apache-2.0"
+implicit-std = false

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_method/src/main.sw

@@ -0,0 +1,7 @@
+contract;
+
+trait A {} {
+    pub fn f(self) -> bool {
+        false
+    }
+}

test/src/e2e_vm_tests/test_programs/should_fail/trait_pub_fn_method/test.toml

@@ -0,0 +1,4 @@
+category = "fail"
+
+# check: pub fn f(self) -> bool {
+# nextln: $()Unnecessary visibility qualifier, `pub` is implied here.