Same module variables must be explicitly shared

Prior to this commit, the following code would work: defmodule Hello do defmacro write do quote do a = 1 end end defmacro read do quote do a end end end require Hello Hello.write Hello.read Although this is convenient, it has many issues: 1. It is not clear at any point the intent of sharing the variables in between the macros 2. Whenever macros from the same module are nested, there is a chance a variable used before and after the nesting to be overriden We address this issue by only allowing variables explicitly marked with var! to be shared. Here is how the example above should be updated: defmodule Hello do defmacro write do quote do var!(a, Hello) = 1 end end defmacro read do quote do var!(a, Hello) end end end require Hello Hello.write Hello.read

Author: José Valim

lib/elixir/include/elixir.hrl

@@ -25,6 +25,7 @@
  local=nil, %% the scope to evaluate local functions against
  context_modules=[], %% modules defined in the current context
  macro_aliases=[], %% keep aliases defined inside a macro
+ macro_counter=0, %% macros expansions counter
  aliases, %% an orddict with aliases by new -> old names
  file, %% the current scope filename
  requires, %% a set with modules required

lib/elixir/lib/kernel/special_forms.ex

@@ -524,7 +524,7 @@ defmodule Kernel.SpecialForms do
 
  ## Hygiene and context
 
- Elixir macros are hygienic via means of deferred resolution.
+ Elixir macros are hygienic by means of deferred resolution.
  This means variables, aliases and imports defined inside the
  quoted refer to the context that defined the macro and not
  the context where the macro is expanded.
@@ -544,7 +544,10 @@ defmodule Kernel.SpecialForms do
  Notice how the third element of the returned tuple is the
  module name. This means that the variable is associated to the
  `ContextSample` module and only code generated by this module
- will be able to access that particular `world` variable.
+ will be able to access that particular `world` variable. Not
+ only variables hygiene, but also imports and aliases hygiene
+ are delimited by context.
+
  While this means macros from the same module could have
  conflicting variables, it also allows different quotes from
  the same module to access them.
@@ -588,31 +591,47 @@ defmodule Kernel.SpecialForms do
  NoHygiene.interference
  a #=> 1
 
- It is important to understand that quoted variables are scoped
- to the module they are defined. That said, even if two modules
- define the same quoted variable `a`, their values are going
- to be independent:
+ Note that you cannot even access variables defined by the same
+ module unless you explicitly give it a context:
 
- defmodule Hygiene1 do
- defmacro var1 do
- quote do: a = 1
+ defmodule Hygiene do
+ defmacro write do
+ quote do
+ a = 1
+ end
  end
- end
 
- defmodule Hygiene2 do
- defmacro var2 do
- quote do: a = 2
+ defmacro read do
+ quote do
+ a
+ end
  end
  end
 
- Calling macros `var1` and `var2` are not going to change their
- each other values for `a`. This is useful because quoted
- variables from different modules cannot conflict. If you desire
- to explicitly access a variable from another module, we can once
- again use `var!` macro, but explicitly passing a second argument:
+ Hygiene.write
+ Hygiene.read
+ #=> no variable a
 
- # Access the variable a from Hygiene1
- quote do: var!(a, Hygiene1) = 2
+ For such, you can explicitly pass the current module scope as
+ argument:
+
+ defmodule ContextHygiene do
+ defmacro write do
+ quote do
+ var!(a, ContextHygiene) = 1
+ end
+ end
+
+ defmacro read do
+ quote do
+ var!(a, ContextHygiene)
+ end
+ end
+ end
+
+ ContextHygiene.write
+ ContextHygiene.read
+ #=> 1
 
  Hygiene for variables can be disabled overall as:
 
@@ -669,7 +688,6 @@ defmodule Kernel.SpecialForms do
  #=> "world"
  end
 
-
  ## Hygiene in imports
 
  Similar to aliases, imports in Elixir are hygienic. Consider the

lib/elixir/src/elixir_dispatch.erl

@@ -89,8 +89,8 @@ dispatch_import(Meta, Name, Args, S, Callback) ->
  { error, internal } ->
  elixir_tracker:record_import(Tuple, ?builtin, Module, S#elixir_scope.function),
  elixir_macros:translate({ Name, Meta, Args }, S);
- { ok, _Receiver, Tree } ->
- translate_expansion(Meta, Tree, S)
+ { ok, Receiver, Tree } ->
+ translate_expansion(Meta, Receiver, Tree, S)
  end
  end.
 
@@ -111,8 +111,8 @@ dispatch_require(Meta, Receiver, Name, Args, S, Callback) ->
  { error, internal } ->
  elixir_tracker:record_remote(Tuple, ?builtin, S#elixir_scope.module, S#elixir_scope.function),
  elixir_macros:translate({ Name, Meta, Args }, S);
- { ok, _Receiver, Tree } ->
- translate_expansion(Meta, Tree, S)
+ { ok, Receiver, Tree } ->
+ translate_expansion(Meta, Receiver, Tree, S)
  end
  end.
 
@@ -222,13 +222,14 @@ expand_macro_named(Meta, Receiver, Name, Arity, Args, Module, S) ->
  Fun = fun Receiver:ProperName/ProperArity,
  expand_macro_fun(Meta, Fun, Receiver, Name, Args, Module, S).
 
-translate_expansion(Meta, Tree, S) ->
+translate_expansion(Meta, Receiver, Tree, S) ->
  Line = ?line(Meta),
+ New = S#elixir_scope.macro_counter + 1,
 
  try
  elixir_translator:translate_each(
- elixir_quote:linify(Line, Tree),
- S
+ elixir_quote:linify(Line, { Receiver, New }, Tree),
+ S#elixir_scope{macro_counter=New}
  )
  catch
  Kind:Reason ->

lib/elixir/src/elixir_quote.erl

@@ -1,27 +1,40 @@
 %% Implements Elixir quote.
 -module(elixir_quote).
 -export([escape/2, erl_escape/3, erl_quote/4,
- linify/2, unquote/4, tail_join/3, join/2]).
+ linify/2, linify/3, unquote/4, tail_join/3, join/2]).
 -include("elixir.hrl").
 
 %% Apply the line from site call on quoted contents.
 linify(Line, Exprs) when is_integer(Line) ->
- do_linify(Line, Exprs).
+ do_linify(Line, nil, Exprs).
 
-do_linify(Line, { Left, Meta, Right }) when is_list(Meta) ->
- NewMeta = case ?line(Meta) of
- 0 -> keystore(line, Meta, Line);
- _ -> Meta
+linify(Line, Var, Exprs) when is_integer(Line) ->
+ do_linify(Line, Var, Exprs).
+
+do_linify(Line, { Receiver, Counter } = Var, { Left, Meta, Receiver }) when is_atom(Left), is_list(Meta) ->
+ NewMeta = case keyfind(counter, Meta) of
+ { counter, _ } -> Meta;
+ _ -> keystore(counter, Meta, Counter)
  end,
- { do_linify(Line, Left), NewMeta, do_linify(Line, Right) };
+ do_tuple_linify(Line, Var, NewMeta, Left, Receiver);
+
+do_linify(Line, Var, { Left, Meta, Right }) when is_list(Meta) ->
+ do_tuple_linify(Line, Var, Meta, Left, Right);
 
-do_linify(Line, { Left, Right }) ->
- { do_linify(Line, Left), do_linify(Line, Right) };
+do_linify(Line, Var, { Left, Right }) ->
+ { do_linify(Line, Var, Left), do_linify(Line, Var, Right) };
 
-do_linify(Line, List) when is_list(List) ->
- [do_linify(Line, X) || X <- List];
+do_linify(Line, Var, List) when is_list(List) ->
+ [do_linify(Line, Var, X) || X <- List];
 
-do_linify(_, Else) -> Else.
+do_linify(_, _, Else) -> Else.
+
+do_tuple_linify(Line, Var, Meta, Left, Right) ->
+ NewMeta = case ?line(Meta) of
+ 0 -> keystore(line, Meta, Line);
+ _ -> Meta
+ end,
+ { do_linify(Line, Var, Left), NewMeta, do_linify(Line, Var, Right) }.
 
 %% Some expressions cannot be unquoted at compilation time.
 %% This function is responsible for doing runtime unquoting.

lib/elixir/src/elixir_scope.erl

@@ -10,7 +10,7 @@
 ]).
 -include("elixir.hrl").
 
-translate_var(Meta, Name, Kind, S, Callback) ->
+translate_var(Meta, Name, Kind, S, Callback) when is_atom(Kind); is_integer(Kind) ->
  Line = ?line(Meta),
  Vars = S#elixir_scope.vars,
  Tuple = { Name, Kind },
@@ -95,7 +95,7 @@ to_ex_env({ Line, #elixir_scope{module=Module,file=File,
  Context, Requires, Functions, Macros, ContextModules, MacroAliases,
  list_vars(Vars) }.
 
-list_vars(Vars) -> [K || { K, _ } <- Vars].
+list_vars(Vars) -> [Pair || { { _, K } = Pair, _ } <- Vars, is_atom(K)].
 
 % Provides a tuple with only the scope information we want to serialize.
 
@@ -109,9 +109,14 @@ serialize(S) ->
 
 serialize_with_vars(Line, S) when is_integer(Line) ->
  { Vars, _ } = orddict:fold(fun({ Key, Kind }, Value, { Acc, Counter }) ->
+ KindKey = if
+ is_atom(Kind) -> atom;
+ is_integer(Kind) -> integer
+ end,
+
  { { cons, Line, { tuple, Line, [
  { atom, Line, Key },
- { atom, Line, Kind },
+ { KindKey, Line, Kind },
  { atom, Line, ?atom_concat(["_@", Counter]) },
  { var, Line, Value }
  ] }, Acc }, Counter + 1 }
@@ -157,6 +162,7 @@ umergev(S1, S2) ->
 umergec(S1, S2) ->
  S1#elixir_scope{
  counter=S2#elixir_scope.counter,
+ macro_counter=S2#elixir_scope.macro_counter,
  extra_guards=S2#elixir_scope.extra_guards,
  super=S2#elixir_scope.super,
  caller=S2#elixir_scope.caller

lib/elixir/src/elixir_translator.erl

@@ -323,9 +323,9 @@ translate_each({ 'super?', Meta, [] }, S) ->
 
 %% Variables
 
-translate_each({ '^', Meta, [ { Name, _, Kind } = Var ] },
+translate_each({ '^', Meta, [ { Name, VarMeta, Kind } = Var ] },
  #elixir_scope{extra=fn_match, extra_guards=Extra} = S) when is_atom(Name), is_atom(Kind) ->
- case orddict:find({ Name, Kind }, S#elixir_scope.backup_vars) of
+ case orddict:find({ Name, var_kind(VarMeta, Kind) }, S#elixir_scope.backup_vars) of
  { ok, Value } ->
  Line = ?line(Meta),
  { TVar, TS } = translate_each(Var, S),
@@ -335,8 +335,8 @@ translate_each({ '^', Meta, [ { Name, _, Kind } = Var ] },
  compile_error(Meta, S#elixir_scope.file, "unbound variable ^~ts", [Name])
  end;
 
-translate_each({ '^', Meta, [ { Name, _, Kind } ] }, #elixir_scope{context=match} = S) when is_atom(Name), is_atom(Kind) ->
- case orddict:find({ Name, Kind }, S#elixir_scope.backup_vars) of
+translate_each({ '^', Meta, [ { Name, VarMeta, Kind } ] }, #elixir_scope{context=match} = S) when is_atom(Name), is_atom(Kind) ->
+ case orddict:find({ Name, var_kind(VarMeta, Kind) }, S#elixir_scope.backup_vars) of
  { ok, Value } ->
  { { var, ?line(Meta), Value }, S };
  error ->
@@ -352,7 +352,7 @@ translate_each({ '^', Meta, [ Expr ] }, S) ->
  "the unary operator ^ can only be used with variables, invalid expression ^~ts", ['Elixir.Macro':to_string(Expr)]);
 
 translate_each({ Name, Meta, Kind }, S) when is_atom(Name), is_atom(Kind) ->
- elixir_scope:translate_var(Meta, Name, Kind, S, fun() ->
+ elixir_scope:translate_var(Meta, Name, var_kind(Meta, Kind), S, fun() ->
  translate_each({ Name, Meta, [] }, S)
  end);
 
@@ -444,6 +444,12 @@ translate_each(Literal, S) ->
 
 %% Helpers
 
+var_kind(Meta, Kind) ->
+ case lists:keyfind(counter, 1, Meta) of
+ { counter, Counter } -> Counter;
+ false -> Kind
+ end.
+
 %% Opts
 
 translate_opts(Meta, Kind, Allowed, Opts, S) ->

lib/elixir/test/elixir/kernel/quote_test.exs

@@ -236,6 +236,22 @@ defmodule Kernel.QuoteTest.VarHygieneTest do
  quote do: var!(a, __MODULE__)
  end
 
+ defmacrop nested(var, do: block) do
+ quote do
+ var = unquote(var)
+ unquote(block)
+ var
+ end
+ end
+
+ defmacrop hat do
+ quote do
+ var = 1
+ ^var = 1
+ var
+ end
+ end
+
  test :no_interference do
  a = 10
  no_interference
@@ -247,12 +263,6 @@ defmodule Kernel.QuoteTest.VarHygieneTest do
  assert a == 1
  end
 
- test :cross_module_no_interference do
- cross_module_no_interference
- no_interference
- assert read_cross_module == 10
- end
-
  test :cross_module_interference do
  cross_module_no_interference
  cross_module_interference
@@ -268,6 +278,18 @@ defmodule Kernel.QuoteTest.VarHygieneTest do
  a = 10
  read_interference
  end
+
+ test :nested do
+ assert (nested 1 do
+ nested 2 do
+ :ok
+ end
+ end) == 1
+ end
+
+ test :hat do
+ assert hat == 1
+ end
 end
 
 defmodule Kernel.QuoteTest.AliasHygiene do