fix: don't confuse localized global for a narrow when reporting unuse…

…d var

Fixes #677.

spec/error_reporting/warning_spec.lua

@@ -100,6 +100,22 @@ describe("warnings", function()
          foo()
       ]], { }))
 
+      it("should report a unused localized global (regression test for #677)", util.check_warnings([[
+         local print = print
+         local type = type
+         local _ENV = nil
+
+         return {
+             say = function (msg: any)
+                 if msg is string then
+                     print(msg)
+                 end
+             end,
+         }
+      ]], {
+         { y = 2, msg = "unused function type" },
+      }))
+
       it("reports when implicitly declared variables redeclare a local (for loop)", util.check_warnings([[
          local i = 1
          for i = 1, 10 do

tl.lua

@@ -4873,6 +4873,7 @@ end
 
 
 
+
 
 local function sorted_keys(m)
    local keys = {}
@@ -6171,7 +6172,7 @@ tl.type_check = function(ast, opts)
    local function unused_warning(name, var)
       local prefix = name:sub(1, 1)
       if var.declared_at and
-         not (var.is_narrowed == "is") and
+         var.is_narrowed ~= "narrow" and
          prefix ~= "_" and
          prefix ~= "@" then
 
@@ -7656,7 +7657,8 @@ tl.type_check = function(ast, opts)
 
    local function widen_in_scope(scope, var)
       assert(scope[var], "no " .. var .. " in scope")
-      if scope[var].is_narrowed then
+      local narrow_mode = scope[var].is_narrowed
+      if narrow_mode and narrow_mode ~= "declaration" then
          if scope[var].narrowed_from then
             scope[var].t = scope[var].narrowed_from
             scope[var].narrowed_from = nil
@@ -8436,7 +8438,7 @@ tl.type_check = function(ast, opts)
             if not f.where then
                t.inferred_at = nil
             end
-            add_var(nil, v, t, "const", "is")
+            add_var(nil, v, t, "const", "narrow")
          end
       end
    end
@@ -9062,7 +9064,7 @@ tl.type_check = function(ast, opts)
 
                   local rt = resolve_tuple_and_nominal(t)
                   if rt.typename ~= "enum" and not same_type(t, infertype) then
-                     add_var(where, var.tk, infer_at(where, infertype), "const", "declaration")
+                     add_var(where, var.tk, infer_at(where, infertype), "const", "narrowed_declaration")
                   end
                end
 
@@ -9123,7 +9125,7 @@ tl.type_check = function(ast, opts)
 
                      if varnode.kind == "variable" and vartype.typename == "union" then
 
-                        add_var(varnode, varnode.tk, val, nil, "is")
+                        add_var(varnode, varnode.tk, val, nil, "narrow")
                      end
                   else
                      node_error(varnode, "variable is not being assigned a value")

tl.tl

@@ -4856,7 +4856,8 @@ function tl.search_module(module_name: string, search_dtl: boolean): string, FIL
 end
 
 local enum Narrow
-   "is"
+   "narrow"
+   "narrowed_declaration"
    "declaration"
 end
 
@@ -6171,7 +6172,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
    local function unused_warning(name: string, var: Variable)
       local prefix <const> = name:sub(1,1)
       if var.declared_at
-         and not (var.is_narrowed == "is")
+         and var.is_narrowed ~= "narrow"
          and prefix ~= "_"
          and prefix ~= "@"
       then
@@ -7656,7 +7657,8 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
 
    local function widen_in_scope(scope: Scope, var: string): boolean
       assert(scope[var], "no " .. var .. " in scope")
-      if scope[var].is_narrowed then
+      local narrow_mode = scope[var].is_narrowed
+      if narrow_mode and narrow_mode ~= "declaration" then
          if scope[var].narrowed_from then
             scope[var].t = scope[var].narrowed_from
             scope[var].narrowed_from = nil
@@ -8436,7 +8438,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
             if not f.where then
                t.inferred_at = nil
             end
-            add_var(nil, v, t, "const", "is")
+            add_var(nil, v, t, "const", "narrow")
          end
       end
    end
@@ -9062,7 +9064,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
 
                   local rt = resolve_tuple_and_nominal(t)
                   if rt.typename ~= "enum" and not same_type(t, infertype) then
-                     add_var(where, var.tk, infer_at(where, infertype), "const", "declaration")
+                     add_var(where, var.tk, infer_at(where, infertype), "const", "narrowed_declaration")
                   end
                end
 
@@ -9123,7 +9125,7 @@ tl.type_check = function(ast: Node, opts: TypeCheckOptions): Result, string
 
                      if varnode.kind == "variable" and vartype.typename == "union" then
                         -- narrow union
-                        add_var(varnode, varnode.tk, val, nil, "is")
+                        add_var(varnode, varnode.tk, val, nil, "narrow")
                      end
                   else
                      node_error(varnode, "variable is not being assigned a value")