Prevent closures from being returned over the bounary

Author: DuncanUszkay1

src/compiler.ts

@@ -2745,6 +2745,24 @@ export class Compiler extends DiagnosticEmitter {
     // Remember that this flow returns
     flow.set(FlowFlags.RETURNS | FlowFlags.TERMINATES);
 
+    // Prevent returning a closure in an exported function, since interop with closures is
+    // not yet supported
+    var returnSignature = returnType.signatureReference;
+    if (returnSignature !== null && flow.parentFunction.is(CommonFlags.EXPORT)) {
+      var returnValueLocalIndex = flow.getTempLocal(returnType).index;
+      var nativeReturnType = returnType.toNativeType();
+      expr = module.flatten([
+        module.local_set(returnValueLocalIndex, expr),
+        this.ifClosure(
+          module.local_get(returnValueLocalIndex, nativeReturnType),
+          this.makeAbort(null, statement), // TODO: throw
+          module.nop()
+        ),
+        module.local_get(returnValueLocalIndex, nativeReturnType)
+      ], nativeReturnType)
+    }
+
+
     // If the last statement anyway, make it the block's return value
     if (isLastInBody && expr != 0 && returnType != Type.void) {
       if (!stmts.length) return expr;

tests/compiler/closure-limitations-runtime.json

@@ -0,0 +1,6 @@
+{
+  "asc_flags": [
+    "--runtime none"
+  ],
+  "skipInstantiate": true
+}

tests/compiler/closure-limitations-runtime.optimized.wat

@@ -0,0 +1,108 @@
+(module
+ (type $none_=>_none (func))
+ (type $i32_i32_i32_i32_=>_none (func (param i32 i32 i32 i32)))
+ (type $none_=>_i32 (func (result i32)))
+ (import "env" "abort" (func $~lib/builtins/abort (param i32 i32 i32 i32)))
+ (memory $0 1)
+ (data (i32.const 1024) "<\00\00\00\01\00\00\00\01\00\00\00<\00\00\00c\00l\00o\00s\00u\00r\00e\00-\00l\00i\00m\00i\00t\00a\00t\00i\00o\00n\00s\00-\00r\00u\00n\00t\00i\00m\00e\00.\00t\00s")
+ (global $~lib/rt/stub/offset (mut i32) (i32.const 0))
+ (export "memory" (memory $0))
+ (export "exportedClosureReturns" (func $closure-limitations-runtime/exportedClosureReturns))
+ (start $~start)
+ (func $closure-limitations-runtime/exportedClosureReturns (result i32)
+  (local $0 i32)
+  (local $1 i32)
+  (local $2 i32)
+  (local $3 i32)
+  global.get $~lib/rt/stub/offset
+  i32.const 16
+  i32.add
+  local.tee $0
+  i32.const 16
+  i32.add
+  local.tee $1
+  memory.size
+  local.tee $3
+  i32.const 16
+  i32.shl
+  local.tee $2
+  i32.gt_u
+  if
+   local.get $3
+   local.get $1
+   local.get $2
+   i32.sub
+   i32.const 65535
+   i32.add
+   i32.const -65536
+   i32.and
+   i32.const 16
+   i32.shr_u
+   local.tee $2
+   local.get $3
+   local.get $2
+   i32.gt_s
+   select
+   memory.grow
+   i32.const 0
+   i32.lt_s
+   if
+    local.get $2
+    memory.grow
+    i32.const 0
+    i32.lt_s
+    if
+     unreachable
+    end
+   end
+  end
+  local.get $1
+  global.set $~lib/rt/stub/offset
+  local.get $0
+  i32.const 16
+  i32.sub
+  local.tee $1
+  i32.const 16
+  i32.store
+  local.get $1
+  i32.const 1
+  i32.store offset=4
+  local.get $1
+  i32.const 3
+  i32.store offset=8
+  local.get $1
+  i32.const 4
+  i32.store offset=12
+  local.get $0
+  i32.const 1
+  i32.store
+  local.get $0
+  i32.const 0
+  i32.store offset=4
+  local.get $0
+  i32.const 4
+  i32.shr_s
+  i32.const -2147483648
+  i32.or
+  local.tee $0
+  i32.const -2147483648
+  i32.and
+  i32.const -2147483648
+  i32.eq
+  if
+   i32.const 0
+   i32.const 1040
+   i32.const 3
+   i32.const 3
+   call $~lib/builtins/abort
+   unreachable
+  end
+  local.get $0
+ )
+ (func $~start
+  i32.const 1104
+  global.set $~lib/rt/stub/offset
+  call $closure-limitations-runtime/exportedClosureReturns
+  drop
+ )
+)

tests/compiler/closure-limitations-runtime.ts

@@ -0,0 +1,7 @@
+export function exportedClosureReturns(): (value: i32) => i32 {
+  var $local0 = 0;
+  return function inner(value: i32) {
+    return $local0;
+  };
+}
+exportedClosureReturns();