From a5dd26b57eac911fc537c07fec5859aa92fac256 Mon Sep 17 00:00:00 2001
From: Hisham Muhammad <hisham@gobolinux.org>
Date: Sat, 21 Oct 2023 14:27:57 -0300
Subject: [PATCH] fix: check records nominally when resolving metamethods for
 operators (#710)

---
 spec/metamethods/add_spec.lua | 31 +++++++++++++++++++++++++++++++
 tl.lua                        | 14 +++++++-------
 tl.tl                         | 14 +++++++-------
 3 files changed, 45 insertions(+), 14 deletions(-)

diff --git a/spec/metamethods/add_spec.lua b/spec/metamethods/add_spec.lua
index aa8466981..89555a9c6 100644
--- a/spec/metamethods/add_spec.lua
+++ b/spec/metamethods/add_spec.lua
@@ -69,4 +69,35 @@ describe("binary metamethod __add", function()
 
       print((10 + s).x)
    ]]))
+
+   it("preserves nominal type checking when resolving metamethods for operators", util.check_type_error([[
+      local type Temperature = record
+         n: number
+         metamethod __add: function(t1: Temperature, t2: Temperature): Temperature
+      end
+
+      local type Date = record
+         n: number
+         metamethod __add: function(t1: Date, t2: Date): Date
+      end
+
+      local temp2: Temperature = { n = 45 }
+      local birthday2 : Date = { n = 34 }
+
+      setmetatable(temp2, {
+         __add = function(t1: Temperature, t2: Temperature): Temperature
+            return { n = t1.n + t2.n }
+         end,
+      })
+
+      setmetatable(birthday2, {
+         __add = function(t1: Date, t2: Date): Date
+            return { n = t1.n + t2.n }
+         end,
+      })
+
+      print((temp2 + birthday2).n)
+   ]], {
+      { y = 26, msg = "Date is not a Temperature" },
+   }))
 end)
diff --git a/tl.lua b/tl.lua
index a17a96991..1288f5297 100644
--- a/tl.lua
+++ b/tl.lua
@@ -7621,7 +7621,7 @@ tl.type_check = function(ast, opts)
       end
    end
 
-   local function check_metamethod(node, op, a, b)
+   local function check_metamethod(node, op, a, b, orig_a, orig_b)
       local method_name
       local where_args
       local args
@@ -7636,11 +7636,11 @@ tl.type_check = function(ast, opts)
       if a and b then
          method_name = binop_to_metamethod[op]
          where_args = { node.e1, node.e2 }
-         args = { typename = "tuple", a, b }
+         args = { typename = "tuple", orig_a, orig_b }
       else
          method_name = unop_to_metamethod[op]
          where_args = { node.e1 }
-         args = { typename = "tuple", a }
+         args = { typename = "tuple", orig_a }
       end
 
       local metamethod = a.meta_fields and a.meta_fields[method_name or ""]
@@ -7679,7 +7679,7 @@ tl.type_check = function(ast, opts)
             return tbl.fields[key]
          end
 
-         local meta_t = check_metamethod(rec, "@index", tbl, STRING)
+         local meta_t = check_metamethod(rec, "@index", tbl, STRING, tbl, STRING)
          if meta_t then
             return meta_t
          end
@@ -8050,7 +8050,7 @@ tl.type_check = function(ast, opts)
          errm, erra, errb = "cannot index object of type %s with %s", orig_a, orig_b
       end
 
-      local meta_t = check_metamethod(anode, "@index", a, orig_b)
+      local meta_t = check_metamethod(anode, "@index", a, orig_b, orig_a, orig_b)
       if meta_t then
          return meta_t
       end
@@ -10004,7 +10004,7 @@ tl.type_check = function(ast, opts)
                node.type = types_op[a.typename]
                local meta_on_operator
                if not node.type then
-                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a)
+                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a, nil, orig_a, nil)
                   if not node.type then
                      node_error(node, "cannot use operator '" .. node.op.op:gsub("%%", "%%%%") .. "' on type %s", resolve_tuple(orig_a))
                   end
@@ -10050,7 +10050,7 @@ tl.type_check = function(ast, opts)
                node.type = types_op[a.typename] and types_op[a.typename][b.typename]
                local meta_on_operator
                if not node.type then
-                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a, b)
+                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a, b, orig_a, orig_b)
                   if not node.type then
                      node_error(node, "cannot use operator '" .. node.op.op:gsub("%%", "%%%%") .. "' for types %s and %s", resolve_tuple(orig_a), resolve_tuple(orig_b))
                      if node.op.op == "or" and is_valid_union(unite({ orig_a, orig_b })) then
diff --git a/tl.tl b/tl.tl
index 1c857442a..ecc7ab67e 100644
--- a/tl.tl
+++ b/tl.tl
@@ -7621,7 +7621,7 @@ 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 function check_metamethod(node: Node, op: string, a: Type, b: Type, orig_a: Type, orig_b: Type): Type, integer
       local method_name: string
       local where_args: {Node}
       local args: Type
@@ -7636,11 +7636,11 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
       if a and b then
          method_name = binop_to_metamethod[op]
          where_args = { node.e1, node.e2 }
-         args = { typename = "tuple", a, b }
+         args = { typename = "tuple", orig_a, orig_b }
       else
          method_name = unop_to_metamethod[op]
          where_args = { node.e1 }
-         args = { typename = "tuple", a }
+         args = { typename = "tuple", orig_a }
       end
 
       local metamethod = a.meta_fields and a.meta_fields[method_name or ""]
@@ -7679,7 +7679,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
             return tbl.fields[key]
          end
 
-         local meta_t = check_metamethod(rec, "@index", tbl, STRING)
+         local meta_t = check_metamethod(rec, "@index", tbl, STRING, tbl, STRING)
          if meta_t then
             return meta_t
          end
@@ -8050,7 +8050,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
          errm, erra, errb = "cannot index object of type %s with %s", orig_a, orig_b
       end
 
-      local meta_t = check_metamethod(anode, "@index", a, orig_b)
+      local meta_t = check_metamethod(anode, "@index", a, orig_b, orig_a, orig_b)
       if meta_t then
          return meta_t
       end
@@ -10004,7 +10004,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
                node.type = types_op[a.typename]
                local meta_on_operator: integer
                if not node.type then
-                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a)
+                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a, nil, orig_a, nil)
                   if not node.type then
                      node_error(node, "cannot use operator '" .. node.op.op:gsub("%%", "%%%%") .. "' on type %s", resolve_tuple(orig_a))
                   end
@@ -10050,7 +10050,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
                node.type = types_op[a.typename] and types_op[a.typename][b.typename]
                local meta_on_operator: integer
                if not node.type then
-                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a, b)
+                  node.type, meta_on_operator = check_metamethod(node, node.op.op, a, b, orig_a, orig_b)
                   if not node.type then
                      node_error(node, "cannot use operator '" .. node.op.op:gsub("%%", "%%%%") .. "' for types %s and %s", resolve_tuple(orig_a), resolve_tuple(orig_b))
                      if node.op.op == "or" and is_valid_union(unite({orig_a, orig_b})) then