Fix __call self

[mtdowling]

Closes #1060

[github-actions]

Teal Playground URL: https://1063--teal-playground-preview.netlify.app

[mbartlett21]

Looks like it will need to be fixed for records method calls as well:

EDIT: Actually reading further it is due to it being a method call rather than __call.

local record Foo
end

local record Selfish
   me: function(self): self
end

function Foo:bar(_a: Selfish)
end

local x: Selfish
local foo: Foo = {}

local myself = x:me()
foo:bar(myself) --> argument 1: Foo is not a Selfish

[mbartlett21]

For a fix for records the below patch seems to work on top of yours. (I've skipped the precompiled env files in the patch below)

diff --git a/teal/check/context.tl b/teal/check/context.tl
index 3b4d3bc..aacbda0 100644
--- a/teal/check/context.tl
+++ b/teal/check/context.tl
@@ -1676,7 +1676,16 @@ function Context:match_record_key(t: Type, rec: Node, key: string): Type, string
       assert(t.fields, "record has no fields!?")
 
       if t.fields[key] then
-         return t.fields[key]
+         local ft = t.fields[key]
+         local ftrep = ft
+         if ft is FunctionType then
+            ftrep = types.map(nil, ft, {
+               ["self"] = function(_: nil, _typ: SelfType): Type, boolean
+                  return t, true
+               end,
+            })
+         end
+         return ftrep
       end
 
       local str = a_type(rec, "string", {})
diff --git a/teal/check/context.lua b/teal/check/context.lua
index 5379c5b..3c20285 100644
--- a/teal/check/context.lua
+++ b/teal/check/context.lua
@@ -1676,7 +1676,16 @@ function Context:match_record_key(t, rec, key)
       assert(t.fields, "record has no fields!?")
 
       if t.fields[key] then
-         return t.fields[key]
+         local ft = t.fields[key]
+         local ftrep = ft
+         if ft.typename == "function" then
+            ftrep = types.map(nil, ft, {
+               ["self"] = function(_, _typ)
+                  return t, true
+               end,
+            })
+         end
+         return ftrep
       end
 
       local str = a_type(rec, "string", {})
diff --git a/spec/lang/call/record_method_spec.lua b/spec/lang/call/record_method_spec.lua
index 5e000dc..a63a64c 100644
--- a/spec/lang/call/record_method_spec.lua
+++ b/spec/lang/call/record_method_spec.lua
@@ -273,9 +273,9 @@ describe("record method call", function()
 
       ]],
       {
-         { y = 9, msg = "argument 1: got integer, expected Foo" },
-         { y = 11, msg = "argument 1: got integer, expected Foo" },
-         { y = 15, msg = "argument 1: got integer, expected Foo" },
+         { y = 9, msg = "argument 1: got integer, expected record Foo" },
+         { y = 11, msg = "argument 1: got integer, expected record Foo" },
+         { y = 15, msg = "argument 1: got integer, expected record Foo" },
       }))
 
       it("for function declared in record body with self as different type from receiver", util.check_type_error([[
diff --git a/spec/lang/metamethods/call_spec.lua b/spec/lang/metamethods/call_spec.lua
index c2b3f6e..98100f1 100644
--- a/spec/lang/metamethods/call_spec.lua
+++ b/spec/lang/metamethods/call_spec.lua
@@ -234,8 +234,8 @@ describe("metamethod __call", function()
       ]]))
    end)
 
-   describe("interface with __call returning self", function()
-      it("resolves self to the interface type, not the caller", util.check([[
+   describe("method returning self", function()
+      it("resolves self to the proper type, not the caller, with __call", util.check([[
          local record Foo
          end
 
@@ -250,7 +250,26 @@ describe("metamethod __call", function()
          local x: ICallable
          local foo: Foo = {}
 
-         foo:bar(x(1))
+         local res = x(1)
+         foo:bar(res)
+      ]]))
+
+      it("resolves self to the proper type, not the caller, with method", util.check([[
+         local record Foo
+         end
+
+         local record Selfish
+            me: function(self): self
+         end
+
+         function Foo:bar(_a: Selfish)
+         end
+
+         local x: Selfish
+         local foo: Foo = {}
+
+         local myself = x:me()
+         foo:bar(myself)
       ]]))
    end)
 end)
diff --git a/spec/lang/stdlib/pcall_spec.lua b/spec/lang/stdlib/pcall_spec.lua
index 3c6e3af..a9f87e3 100644
--- a/spec/lang/stdlib/pcall_spec.lua
+++ b/spec/lang/stdlib/pcall_spec.lua
@@ -114,6 +114,6 @@ describe("pcall", function()
          print(err)
       end
    ]], {
-      { msg = "argument 2: got integer, expected Text" }
+      { msg = "argument 2: got integer, expected record Text" }
    }))
 end)
diff --git a/spec/lang/stdlib/xpcall_spec.lua b/spec/lang/stdlib/xpcall_spec.lua
index 13dc37d..76cbfea 100644
--- a/spec/lang/stdlib/xpcall_spec.lua
+++ b/spec/lang/stdlib/xpcall_spec.lua
@@ -157,7 +157,7 @@ describe("xpcall", function()
       local myText: Text = {}
       xpcall(myText.print, msgh, 12)
    ]], {
-      { msg = "argument 3: got integer, expected Text" }
+      { msg = "argument 3: got integer, expected record Text" }
    }))
 
 end)

[hishamhm]

Thank you both for looking into this! I haven't looked closely at it yet, but from reading the PR and patch, I wonder if the root cause is that we're missing a call to Context:resolve_self, or if we're calling it at the wrong place...

[mbartlett21]

Both what we've added aren't quite the same as Context:resolve_self, as there is either no self variable or it is for an outer scope at that point. And I did try adding an extra parameter to resolve_self to provide an 'expectedself' type, but that has some other inscrutable errors because it uses typedecl_to_nominal, and that then makes some local type X = Y in the compiler complain that Y isn't a type.

I also did try to just have the field access do local ftrep = types.map(nil, ft, {}) (which duplicates the map but leaves the typeid the same), but that makes it go weird with trying to use functions declared after the record definition. (Such as most of the compiler).

---

Also I've found another contrived test case that breaks now because it resolves self to the wrong type.

local interface ReturnsGeneric<T>
   getgen: function(self): T
   metamethod __call: function(self): T
end

local record Test
end

function Test:testgen(g: ReturnsGeneric<self>, s: self): Test
   local checkself: Test = s -- this is to verify that self here resolves correctly
   return g:getgen() -- in return value: got interface ReturnsGeneric, expected Test
end
function Test:testgencall(g: ReturnsGeneric<self>, s: self): Test
   local checkself: Test = s -- this is to verify that self here resolves correctly
   return g() -- in return value: got interface ReturnsGeneric, expected Test
end

---

I'm happy to accept these existing changes as is for now as it is fairly well-defined (the __call metamethod will always have the correct self apart from generics) and probably iterate on getting general functions and generics to work.

[mtdowling]

Thanks, @mbartlett21! I've incorporated your recommendations into the PR.

[mbartlett21]

I've just done a push after running make clean; make on your branch (that way the tl.lua and teal/precompiled/default_env.lua files get updated)

[mbartlett21]

Oh and that now looks like it conflicts with my changes in 59deb86 . @mtdowling Are you happy for me to rebase or you to rebase? (Generally I reset the tl.lua and other changes that conflict and then run make clean; make at each commit)

[hishamhm]

@mbartlett21 @mtdowling feel free to merge this when you get to a resolution regarding the rebase 👍

[mtdowling]

@mbartlett21 no worries— if you don’t mind handling the rebase, that would great!

[mbartlett21]

Thank you and sorted.