fix(throw): compile last throw expression as throw statement not `ret…

…urn throw ...`

src/transform/__snapshots__/throw.test.js.snap

@@ -1,8 +1,17 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
 exports[`throw transforms throw 1`] = `
-"const foo = bar || throw err(\`spam\`);
-Object.assign(module.exports, {
-  foo
-});"
+"bar => {
+  const ˆvalue_1 = true;
+
+  if (ˆvalue_1 === has_err(bar)) {
+    throw err(\`spam\`);
+  }
+
+  {
+    return bar;
+  }
+};
+
+Object.assign(module.exports, {});"
 `;

src/transform/js/do-expression.js

@@ -1,6 +1,7 @@
 import {
   assignmentExpression, returnStatement, callExpression,
-  arrowFunctionExpression
+  arrowFunctionExpression,
+  expressionStatement
 } from '@babel/types';
 import {lets, assign, undef} from '../../types';
 
@@ -40,9 +41,16 @@ function* last_expressions(path) {
 
 const replace_with_return = (path)=> {
   for (const expr of last_expressions(path)) {
-    expr.replaceWith(
-      returnStatement(expr.node.expression)
-    );
+    if (expr.node.expression.operator === 'throw') {
+      // no `return throw ...`
+      expr.replaceWith(
+        expressionStatement(expr.node.expression)
+      );
+    } else {
+      expr.replaceWith(
+        returnStatement(expr.node.expression)
+      );
+    }
 
     // TODO: no need for e.g. breaks after a return
     const sibl = expr.getSibling(expr.key+1);

src/transform/throw.test.js

@@ -5,7 +5,10 @@ describe('throw', ()=> {
   it('transforms throw', ()=> {
     expect(
       fink2js(`
-        foo = bar || throw err('spam')
+        fn bar:
+          match true:
+            has_err(bar): throw err('spam')
+            else: bar
       `)
     ).toMatchSnapshot();
   });