feat(parser): recover old-style fallbacks (#135)

crates/ast/src/ast/ty.rs

@@ -23,6 +23,12 @@ impl Type<'_> {
     pub fn is_custom(&self) -> bool {
         self.kind.is_custom()
     }
+
+    /// Returns `true` if the type is a function.
+    #[inline]
+    pub fn is_function(&self) -> bool {
+        matches!(self.kind, TypeKind::Function(_))
+    }
 }
 
 /// The kind of a type.

crates/parse/src/parser/item.rs

@@ -710,6 +710,27 @@ impl<'sess, 'ast> Parser<'sess, 'ast> {
             }
         };
 
+        if ty.is_function()
+            && flags == VarFlags::STATE_VAR
+            && self.check_noexpect(&TokenKind::OpenDelim(Delimiter::Brace))
+        {
+            let msg = "expected a state variable declaration";
+            let note = "this style of fallback function has been removed; use the `fallback` or `receive` keywords instead";
+            self.dcx().err(msg).span(self.token.span).note(note).emit();
+            let _ = self.parse_block()?;
+            return Ok(VariableDefinition {
+                span: lo.to(self.prev_token.span),
+                ty,
+                visibility: None,
+                mutability: None,
+                data_location: None,
+                override_: None,
+                indexed: false,
+                name: None,
+                initializer: None,
+            });
+        }
+
         let mut data_location = None;
         let mut visibility = None;
         let mut mutability = None;

tests/ui/parser/old_fallback.sol

@@ -0,0 +1,11 @@
+// https://github.com/foundry-rs/foundry/issues/9349
+
+pragma solidity >=0.4.22 <0.6;
+
+contract BugReport {
+    function() external payable { //~ ERROR: expected a state variable declaration
+        deposit();
+        uint
+    } //~ ERROR: expected
+    function deposit() public payable {}
+}

tests/ui/parser/old_fallback.stderr

@@ -0,0 +1,19 @@
+error: expected a state variable declaration
+  --> ROOT/tests/ui/parser/old_fallback.sol:LL:CC
+   |
+LL |     function() external payable {
+   |                                 ^
+   |
+   = note: this style of fallback function has been removed; use the `fallback` or `receive` keywords instead
+
+error: expected one of `(`, `.`, `;`, `?`, `[`, `payable`, `pure`, `view`, or `{`, found `}`
+  --> ROOT/tests/ui/parser/old_fallback.sol:LL:CC
+   |
+LL |         uint
+   |             ^ expected one of 9 possible tokens
+LL |     }
+   |     ^ unexpected token
+   |
+
+error: aborting due to 2 previous errors
+