Report an error in resolver when trying to return from top-level

src/resolver/mod.rs

@@ -13,6 +13,12 @@ use self::resolution_error::ResolutionError;
 pub struct Resolver {
     locals: HashMap<NameExpr, usize>,
     scopes: Vec<HashMap<Name, bool>>,
+    current_function: Option<FunctionType>,
+}
+
+#[derive(Debug)]
+enum FunctionType {
+    Function,
 }
 
 type Result<T> = std::result::Result<T, ResolutionError>;
@@ -45,9 +51,18 @@ impl Resolver {
             } => {
                 self.declare(name);
                 self.define(name);
-                self.resolve_function(parameters, body)
+                self.resolve_function(parameters, body, FunctionType::Function)
+            }
+            Return(expr) => {
+                if self.current_function.is_none() {
+                    Err(ResolutionError::InvalidReturn {
+                        src: statement.src.clone(),
+                        location: statement.location,
+                    })
+                } else {
+                    expr.iter().try_for_each(|e| self.resolve_expr(e))
+                }
             }
-            Return(expr) => expr.iter().try_for_each(|e| self.resolve_expr(e)),
             Block(statements) => self.resolve_block(statements),
             If {
                 condition,
@@ -72,14 +87,21 @@ impl Resolver {
         Ok(())
     }
 
-    fn resolve_function(&mut self, parameters: &[Name], body: &[Stmt]) -> Result<()> {
+    fn resolve_function(
+        &mut self,
+        parameters: &[Name],
+        body: &[Stmt],
+        function_type: FunctionType,
+    ) -> Result<()> {
+        let enclosing_function = std::mem::replace(&mut self.current_function, Some(function_type));
         self.begin_scope();
         parameters.iter().for_each(|p| {
             self.declare(p);
             self.define(p);
         });
         self.resolve_statements(body)?;
         self.end_scope();
+        self.current_function = enclosing_function;
         Ok(())
     }
 

src/resolver/resolution_error.rs

@@ -14,4 +14,11 @@ pub enum ResolutionError {
         #[label("here")]
         location: SourceSpan,
     },
+    #[error("Can't return from top-level code")]
+    InvalidReturn {
+        #[source_code]
+        src: Arc<NamedSource<String>>,
+        #[label("here")]
+        location: SourceSpan,
+    },
 }

tests/closure.lox

@@ -15,4 +15,4 @@ counter();
 counter();
 ----
 1
-2
+2

tests/resolver_errors/recursive_var.lox

@@ -23,4 +23,4 @@ var a = 1;
   "severity": "error"
 }
 ----
----- (no newline)
+---- (no newline)

tests/resolver_errors/return_from_top.lox

@@ -0,0 +1,22 @@
+error
+return 1;
+----
+----
+{
+  "causes": [],
+  "filename": "tests/resolver_errors/return_from_top.lox",
+  "labels": [
+    {
+      "label": "here",
+      "span": {
+        "length": 9,
+        "offset": 0
+      }
+    }
+  ],
+  "message": "Can't return from top-level code",
+  "related": [],
+  "severity": "error"
+}
+----
+---- (no newline)

tests/static_scope.lox

@@ -10,4 +10,4 @@ var a = "global";
 }
 ----
 global
-global
+global