Fix top-level yield in iife mode

Fixes #1659

source/parser.hera

@@ -222,6 +222,7 @@ Program
       bare: true,
       root: true,
       topLevelAwait: hasAwait(statements),
+      topLevelYield: hasYield(statements),
     }
     processProgram(program)
     return program

source/parser/lib.civet

@@ -1549,8 +1549,10 @@ function processProgram(root: BlockStatement): void
   let rootIIFE: ASTNode
   if config.iife or config.repl
     // Avoid top-level await if code is async (same as CoffeeScript),
+    // and avoid top-level yield* if code is a generator,
     // so that code works in CommonJS environment and so REPL can eval it
-    rootIIFE = wrapIIFE root.expressions, root.topLevelAwait
+    rootIIFE = wrapIIFE root.expressions, root.topLevelAwait,
+      if root.topLevelYield then "*"
     newExpressions: StatementTuple[] := [['', rootIIFE]]
     root.children = root.children.map & is root.expressions ? newExpressions : &
     root.expressions = newExpressions

source/parser/types.civet

@@ -601,6 +601,7 @@ export type BlockStatement =
   implicitlyReturned?: boolean  // fat arrow function with no braces
   root?: boolean  // is this the global root block for the program?
   topLevelAwait?: boolean // for root block, is there top-level `await`? (before any IIFE wrapping)
+  topLevelYield?: boolean // for root block, is there top-level `yield`? (before any IIFE wrapping)
   parent?: Parent
 
 export type ImportDeclaration

test/iife.civet

@@ -38,6 +38,15 @@ describe "iife directive", ->
     (async ()=>{return console.log((await fetch('https://civet.dev')).status)})()
   """
 
+  testCase """
+    generator
+    ---
+    "civet iife"
+    yield 5
+    ---
+    (function*(){yield 5})()
+  """
+
 describe "repl directive", ->
   testCase """
     top-level declarations