From f6fc5dc3e32e579fc655070daa64f874239abb02 Mon Sep 17 00:00:00 2001
From: Hisham Muhammad <hisham@gobolinux.org>
Date: Wed, 13 Sep 2023 20:00:54 -0300
Subject: [PATCH] fix: check __index on `:` style calls

Fixes #692.
---
 spec/metamethods/index_spec.lua |  9 +++++
 tl.lua                          | 68 +++++++++++++++++++--------------
 tl.tl                           | 68 +++++++++++++++++++--------------
 3 files changed, 87 insertions(+), 58 deletions(-)

diff --git a/spec/metamethods/index_spec.lua b/spec/metamethods/index_spec.lua
index 88b9a5e80..de924ea0b 100644
--- a/spec/metamethods/index_spec.lua
+++ b/spec/metamethods/index_spec.lua
@@ -180,4 +180,13 @@ describe("metamethod __index", function()
         print(self.x)
       end
    ]]))
+
+   it("passes regression test for #692", util.check([[
+      local record R
+         metamethod __index: function(self: R, key: string): function(R)
+      end
+
+      R.hello(R)
+      R:hello()
+   ]]))
 end)
diff --git a/tl.lua b/tl.lua
index 050c837c2..0c45f142d 100644
--- a/tl.lua
+++ b/tl.lua
@@ -7617,6 +7617,40 @@ tl.type_check = function(ast, opts)
       end
    end
 
+   local function check_metamethod(node, op, a, b)
+      local method_name
+      local where_args
+      local args
+      local meta_on_operator = 1
+
+      if lax and ((a and is_unknown(a)) or (b and is_unknown(b))) then
+         return UNKNOWN, nil
+      elseif not a.meta_fields and not (b and b.meta_fields) then
+         return nil, nil
+      end
+
+      if a and b then
+         method_name = binop_to_metamethod[op]
+         where_args = { node.e1, node.e2 }
+         args = { typename = "tuple", a, b }
+      else
+         method_name = unop_to_metamethod[op]
+         where_args = { node.e1 }
+         args = { typename = "tuple", a }
+      end
+
+      local metamethod = a.meta_fields and a.meta_fields[method_name or ""]
+      if (not metamethod) and b and op ~= "@index" then
+         metamethod = b.meta_fields and b.meta_fields[method_name or ""]
+         meta_on_operator = 2
+      end
+      if metamethod then
+         return resolve_tuple_and_nominal(type_check_function_call(node, where_args, metamethod, args, nil, false, 0)), meta_on_operator
+      else
+         return nil, nil
+      end
+   end
+
    local function match_record_key(tbl, rec, key)
       assert(type(tbl) == "table")
       assert(type(rec) == "table")
@@ -7641,6 +7675,11 @@ tl.type_check = function(ast, opts)
             return tbl.fields[key]
          end
 
+         local meta_t = check_metamethod(rec, "@index", tbl, STRING)
+         if meta_t then
+            return meta_t
+         end
+
          if rec.kind == "variable" then
             return nil, "invalid key '" .. key .. "' in record '" .. rec.tk .. "' of type %s"
          else
@@ -7926,35 +7965,6 @@ tl.type_check = function(ast, opts)
       end
    end
 
-   local function check_metamethod(node, op, a, b)
-      local method_name
-      local where_args
-      local args
-      local meta_on_operator = 1
-      if a and b then
-         method_name = binop_to_metamethod[op]
-         where_args = { node.e1, node.e2 }
-         args = { typename = "tuple", a, b }
-      else
-         method_name = unop_to_metamethod[op]
-         where_args = { node.e1 }
-         args = { typename = "tuple", a }
-      end
-
-      local metamethod = a.meta_fields and a.meta_fields[method_name or ""]
-      if (not metamethod) and b and op ~= "@index" then
-         metamethod = b.meta_fields and b.meta_fields[method_name or ""]
-         meta_on_operator = 2
-      end
-      if metamethod then
-         return resolve_tuple_and_nominal(type_check_function_call(node, where_args, metamethod, args, nil, false, 0)), meta_on_operator
-      elseif lax and ((a and is_unknown(a)) or (b and is_unknown(b))) then
-         return UNKNOWN, nil
-      else
-         return nil, nil
-      end
-   end
-
    local function type_check_index(anode, bnode, a, b)
       local orig_a = a
       local orig_b = b
diff --git a/tl.tl b/tl.tl
index 6912a44a5..f434f1f60 100644
--- a/tl.tl
+++ b/tl.tl
@@ -7617,6 +7617,40 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
       end
    end
 
+   local function check_metamethod(node: Node, op: string, a: Type, b: Type): Type, integer
+      local method_name: string
+      local where_args: {Node}
+      local args: Type
+      local meta_on_operator = 1
+
+      if lax and ((a and is_unknown(a)) or (b and is_unknown(b))) then
+         return UNKNOWN, nil
+      elseif not a.meta_fields and not (b and b.meta_fields) then
+         return nil, nil
+      end
+
+      if a and b then
+         method_name = binop_to_metamethod[op]
+         where_args = { node.e1, node.e2 }
+         args = { typename = "tuple", a, b }
+      else
+         method_name = unop_to_metamethod[op]
+         where_args = { node.e1 }
+         args = { typename = "tuple", a }
+      end
+
+      local metamethod = a.meta_fields and a.meta_fields[method_name or ""]
+      if (not metamethod) and b and op ~= "@index" then
+         metamethod = b.meta_fields and b.meta_fields[method_name or ""]
+         meta_on_operator = 2
+      end
+      if metamethod then
+         return resolve_tuple_and_nominal(type_check_function_call(node, where_args, metamethod, args, nil, false, 0)), meta_on_operator
+      else
+         return nil, nil
+      end
+   end
+
    local function match_record_key(tbl: Type, rec: Node, key: string): Type, string
       assert(type(tbl) == "table")
       assert(type(rec) == "table")
@@ -7641,6 +7675,11 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
             return tbl.fields[key]
          end
 
+         local meta_t = check_metamethod(rec, "@index", tbl, STRING)
+         if meta_t then
+            return meta_t
+         end
+
          if rec.kind == "variable" then
             return nil, "invalid key '" .. key .. "' in record '" .. rec.tk .. "' of type %s"
          else
@@ -7926,35 +7965,6 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
       end
    end
 
-   local function check_metamethod(node: Node, op: string, a: Type, b: Type): Type, integer
-      local method_name: string
-      local where_args: {Node}
-      local args: Type
-      local meta_on_operator = 1
-      if a and b then
-         method_name = binop_to_metamethod[op]
-         where_args = { node.e1, node.e2 }
-         args = { typename = "tuple", a, b }
-      else
-         method_name = unop_to_metamethod[op]
-         where_args = { node.e1 }
-         args = { typename = "tuple", a }
-      end
-
-      local metamethod = a.meta_fields and a.meta_fields[method_name or ""]
-      if (not metamethod) and b and op ~= "@index" then
-         metamethod = b.meta_fields and b.meta_fields[method_name or ""]
-         meta_on_operator = 2
-      end
-      if metamethod then
-         return resolve_tuple_and_nominal(type_check_function_call(node, where_args, metamethod, args, nil, false, 0)), meta_on_operator
-      elseif lax and ((a and is_unknown(a)) or (b and is_unknown(b))) then
-         return UNKNOWN, nil
-      else
-         return nil, nil
-      end
-   end
-
    local function type_check_index(anode: Node, bnode: Node, a: Type, b: Type): Type
       local orig_a = a
       local orig_b = b