Allow returning Procs from top-level funs (#14917)

spec/compiler/codegen/proc_spec.cr

@@ -862,6 +862,59 @@ describe "Code gen: proc" do
     ))
   end
 
+  it "returns proc as function pointer inside top-level fun (#14691)" do
+    run(<<-CRYSTAL, Int32).should eq(8)
+      def raise(msg)
+        while true
+        end
+      end
+
+      fun add : Int32, Int32 -> Int32
+        ->(x : Int32, y : Int32) { x &+ y }
+      end
+
+      add.call(3, 5)
+      CRYSTAL
+  end
+
+  it "returns ProcPointer inside top-level fun (#14691)" do
+    run(<<-CRYSTAL, Int32).should eq(8)
+      def raise(msg)
+        while true
+        end
+      end
+
+      fun foo(x : Int32) : Int32
+        x &+ 5
+      end
+
+      fun bar : Int32 -> Int32
+        ->foo(Int32)
+      end
+
+      bar.call(3)
+      CRYSTAL
+  end
+
+  it "raises if returning closure from top-level fun (#14691)" do
+    run(<<-CRYSTAL).to_b.should be_true
+      require "prelude"
+
+      @[Raises]
+      fun foo(x : Int32) : -> Int32
+        -> { x }
+      end
+
+      begin
+        foo(1)
+      rescue
+        true
+      else
+        false
+      end
+      CRYSTAL
+  end
+
   it "closures var on ->var.call (#8584)" do
     run(%(
       def bar(x)

src/compiler/crystal/codegen/fun.cr

@@ -236,17 +236,22 @@ class Crystal::CodeGenVisitor
     # Check if this def must use the C calling convention and the return
     # value must be either casted or passed by sret
     if target_def.c_calling_convention? && target_def.abi_info?
+      return_type = target_def.body.type
+      if return_type.proc?
+        @last = check_proc_is_not_closure(@last, return_type)
+      end
+
       abi_info = abi_info(target_def)
-      ret_type = abi_info.return_type
-      if cast = ret_type.cast
+      abi_ret_type = abi_info.return_type
+      if cast = abi_ret_type.cast
         casted_last = pointer_cast @last, cast.pointer
         last = load cast, casted_last
         ret last
         return
       end
 
-      if (attr = ret_type.attr) && attr == LLVM::Attribute::StructRet
-        store load(llvm_type(target_def.body.type), @last), context.fun.params[0]
+      if (attr = abi_ret_type.attr) && attr == LLVM::Attribute::StructRet
+        store load(llvm_type(return_type), @last), context.fun.params[0]
         ret
         return
       end