fix: check validity of goto target

Fixes #1121.

Author: hishamhm

spec/lang/statement/goto_spec.lua

@@ -107,4 +107,38 @@ describe("goto", function()
       end
    ]]))
 
+   it("rejects a goto into the scope of local in same block (regression test for #1121)", util.check_type_error([[
+      goto finish
+      local _foo  =  0
+      :: finish ::
+      local _bar  =  0
+   ]], {
+      { y = 1, msg = "goto jumps into scope of a local variable" }
+   }))
+
+   it("can jump upwards (regression test for #1121)", util.check([[
+      local _foo = 0
+      :: finish ::
+      goto finish
+   ]]))
+
+   it("can jump over out-of-scope locals (regression test for #1121)", util.check([[
+      do
+         goto finish
+         local _foo  =  0
+      end
+      :: finish ::
+      local _bar  =  0
+   ]]))
+
+   it("rejects a goto into the scope of local in outer block (regression test for #1121)", util.check_type_error([[
+      do
+         goto finish
+      end
+      local _foo  =  0
+      :: finish ::
+      local _bar  =  0
+   ]], {
+      { y = 2, msg = "goto jumps into scope of a local variable" }
+   }))
 end)

teal/ast.lua

@@ -232,6 +232,7 @@ local parse_typeargs_if_any
 
 
 
+
 
 
 local ast = {}

teal/ast.tl

@@ -189,6 +189,7 @@ local record Node
 
    -- goto
    label: string
+   n_scope_vars: integer
 
    -- label
    used_label: boolean

teal/check/visitors.lua

@@ -783,6 +783,16 @@ local function assert_is_a(ctx, w, t1, t2, ectx, name)
    return ok
 end
 
+local function count_scope_vars(self)
+   local n = 0
+   for i = 1, #self.st do
+      for _, _ in pairs(self.st[i].vars) do
+         n = n + 1
+      end
+   end
+   return n
+end
+
 visit_node.cbs = {
    ["statements"] = {
       before = function(self, node)
@@ -1052,14 +1062,17 @@ visit_node.cbs = {
             end
          end
 
-
          local scope = self.st[#self.st]
          if scope.pending_labels and scope.pending_labels[label_id] then
+            local n_scope_vars = count_scope_vars(self)
+            for _, goto_node in ipairs(scope.pending_labels[label_id]) do
+               if n_scope_vars > goto_node.n_scope_vars then
+                  self.errs:add(goto_node, "goto jumps into scope of a local variable")
+               end
+            end
             node.used_label = true
             scope.pending_labels[label_id] = nil
-
          end
-
       end,
       after = function()
          return NONE
@@ -1084,6 +1097,7 @@ visit_node.cbs = {
             scope.pending_labels = scope.pending_labels or {}
             scope.pending_labels[label_id] = scope.pending_labels[label_id] or {}
             table.insert(scope.pending_labels[label_id], node)
+            node.n_scope_vars = count_scope_vars(self)
          end
 
          return NONE

teal/check/visitors.tl

@@ -783,6 +783,16 @@ local function assert_is_a(ctx: Context, w: Where, t1: Type, t2: Type, ectx?: No
    return ok
 end
 
+local function count_scope_vars(self: Context): integer
+   local n = 0
+   for i = 1, #self.st do
+      for _, _ in pairs(self.st[i].vars) do
+         n = n + 1
+      end
+   end
+   return n
+end
+
 visit_node.cbs = {
    ["statements"] = {
       before = function(self: Context, node: Node)
@@ -1052,14 +1062,17 @@ visit_node.cbs = {
             end
          end
 
-         --for i = #self.st, 1, -1 do
-            local scope = self.st[#self.st]
-            if scope.pending_labels and scope.pending_labels[label_id] then
-               node.used_label = true
-               scope.pending_labels[label_id] = nil
-               --break
+         local scope = self.st[#self.st]
+         if scope.pending_labels and scope.pending_labels[label_id] then
+            local n_scope_vars = count_scope_vars(self)
+            for _, goto_node in ipairs(scope.pending_labels[label_id]) do
+               if n_scope_vars > goto_node.n_scope_vars then
+                  self.errs:add(goto_node, "goto jumps into scope of a local variable")
+               end
             end
-         --end
+            node.used_label = true
+            scope.pending_labels[label_id] = nil
+         end
       end,
       after = function(): Type
          return NONE
@@ -1084,6 +1097,7 @@ visit_node.cbs = {
             scope.pending_labels = scope.pending_labels or {}
             scope.pending_labels[label_id] = scope.pending_labels[label_id] or {}
             table.insert(scope.pending_labels[label_id], node)
+            node.n_scope_vars = count_scope_vars(self)
          end
 
          return NONE

tl.lua

@@ -494,6 +494,7 @@ local parse_typeargs_if_any
 
 
 
+
 
 
 local ast = {}
@@ -8310,6 +8311,16 @@ local function assert_is_a(ctx, w, t1, t2, ectx, name)
    return ok
 end
 
+local function count_scope_vars(self)
+   local n = 0
+   for i = 1, #self.st do
+      for _, _ in pairs(self.st[i].vars) do
+         n = n + 1
+      end
+   end
+   return n
+end
+
 visit_node.cbs = {
    ["statements"] = {
       before = function(self, node)
@@ -8579,14 +8590,17 @@ visit_node.cbs = {
             end
          end
 
-
          local scope = self.st[#self.st]
          if scope.pending_labels and scope.pending_labels[label_id] then
+            local n_scope_vars = count_scope_vars(self)
+            for _, goto_node in ipairs(scope.pending_labels[label_id]) do
+               if n_scope_vars > goto_node.n_scope_vars then
+                  self.errs:add(goto_node, "goto jumps into scope of a local variable")
+               end
+            end
             node.used_label = true
             scope.pending_labels[label_id] = nil
-
          end
-
       end,
       after = function()
          return NONE
@@ -8611,6 +8625,7 @@ visit_node.cbs = {
             scope.pending_labels = scope.pending_labels or {}
             scope.pending_labels[label_id] = scope.pending_labels[label_id] or {}
             table.insert(scope.pending_labels[label_id], node)
+            node.n_scope_vars = count_scope_vars(self)
          end
 
          return NONE