make code_lowered type stable

Author: aviatesk

base/reflection.jl

@@ -1126,21 +1126,23 @@ function code_lowered(@nospecialize(f), @nospecialize(t=Tuple); generated::Bool=
         throw(ArgumentError("'debuginfo' must be either :source or :none"))
     end
     world = get_world_counter()
-    world == typemax(UInt) && error("code reflection cannot be used from generated functions")
-    return map(method_instances(f, t, world)) do m
+    ret = CodeInfo[]
+    for m in method_instances(f, t, world)
         if generated && hasgenerator(m)
             if may_invoke_generator(m)
-                return ccall(:jl_code_for_staged, Any, (Any, UInt), m, world)::CodeInfo
+                push!(ret, ccall(:jl_code_for_staged, Any, (Any, UInt), m, world)::CodeInfo)
             else
-                error("Could not expand generator for `@generated` method ", m, ". ",
-                      "This can happen if the provided argument types (", t, ") are ",
-                      "not leaf types, but the `generated` argument is `true`.")
+                error(
+                    "Could not expand generator for `@generated` method ", m, ". ",
+                    "This can happen if the provided argument types (", lt, ") are ",
+                    "not leaf types, but the `generated` argument is `true`.")
             end
         end
         code = uncompressed_ir(m.def::Method)
         debuginfo === :none && remove_linenums!(code)
-        return code
+        push!(ret, code)
     end
+    return ret
 end
 
 hasgenerator(m::Method) = isdefined(m, :generator)

test/reflection.jl

@@ -1193,3 +1193,6 @@ end
 @test Base.isexported(Mod52812, :b)
 @test Base.ispublic(Mod52812, :a)
 @test Base.ispublic(Mod52812, :b)
+
+@test Base.infer_return_type(code_lowered, (Any,)) == Vector{Core.CodeInfo}
+@test Base.infer_return_type(code_lowered, (Any,Any)) == Vector{Core.CodeInfo}