File 2161-Allow-variables-bound-in-try-to-be-used-in... of Package erlang

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File 2161-Allow-variables-bound-in-try-to-be-used-in-of-clause.patch of Package erlang (Revision 02775a1e4b9808dffc0e5f09fec6e4ec)

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From 8a9a443a454327cbf17120f63664caa0973e9050 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Tue, 16 Jun 2020 05:06:23 +0200
Subject: [PATCH] Allow variables bound in 'try' to be used in 'of' clauses

The following program would not compile:

-module(foo).
    baz() ->
        try Bar = 42 of
            _ -> Bar
        after
	    ok
        end.

The error message is "foo.erl:4: variable 'Bar' unsafe in 'try' (line 3)".

There is no reason for 'Bar' to be unsafe, because if the pattern
after `of` is reached, `Bar = 42` must have been successfully evaluated.

https://bugs.erlang.org/browse/ERL-1281
---
 lib/compiler/src/v3_core.erl         | 28 +++++++----
 lib/compiler/test/trycatch_SUITE.erl | 73 +++++++++++++++++++++++++++-
 lib/stdlib/src/erl_lint.erl          | 12 ++---
 lib/stdlib/test/erl_lint_SUITE.erl   |  5 +-
 4 files changed, 97 insertions(+), 21 deletions(-)

diff --git a/lib/compiler/src/v3_core.erl b/lib/compiler/src/v3_core.erl
index d318fab15c..8037bb6efc 100644
--- a/lib/compiler/src/v3_core.erl
+++ b/lib/compiler/src/v3_core.erl
@@ -2406,13 +2406,16 @@ uexpr(#icall{anno=A,module=Mod,name=Name,args=As}, _, St) ->
     Used = union([lit_vars(Mod),lit_vars(Name),lit_list_vars(As)]),
     {#icall{anno=A#a{us=Used},module=Mod,name=Name,args=As},St};
 uexpr(#itry{anno=A,args=As0,vars=Vs,body=Bs0,evars=Evs,handler=Hs0}, Ks, St0) ->
-    %% Note that we export only from body and exception.
+    %% No variables are exported from try/catch. Starting in OTP 24,
+    %% variables bound in the argument (the code between the 'try' and
+    %% the 'of' keywords) are exported to the body (the code following
+    %% the 'of' keyword).
     {As1,St1} = uexprs(As0, Ks, St0),
-    {Bs1,St2} = uexprs(Bs0, Ks, St1),
+    ArgKs = union(Ks, new_in_any(As1)),
+    {Bs1,St2} = uexprs(Bs0, ArgKs, St1),
     {Hs1,St3} = uexprs(Hs0, Ks, St2),
     Used = intersection(used_in_any(Bs1++Hs1++As1), Ks),
-    New = new_in_all(Bs1++Hs1),
-    {#itry{anno=A#a{us=Used,ns=New},
+    {#itry{anno=A#a{us=Used,ns=[]},
 	   args=As1,vars=Vs,body=Bs1,evars=Evs,handler=Hs1},St3};
 uexpr(#icatch{anno=A,body=Es0}, Ks, St0) ->
     {Es1,St1} = uexprs(Es0, Ks, St0),
@@ -2833,13 +2836,18 @@ cexpr(#ireceive2{anno=A,clauses=Lcs,timeout=Lto,action=Les}, As, St0) ->
     {#c_receive{anno=A#a.anno,
 		clauses=Ccs,timeout=Cto,action=Ces},
      Exp,A#a.us,St3};
-cexpr(#itry{anno=A,args=La,vars=Vs,body=Lb,evars=Evs,handler=Lh}, As, St0) ->
-    Exp = intersection(A#a.ns, As),           %Exports
-    {Ca,_Us1,St1} = cexprs(La, [], St0),
-    {Cb,_Us2,St2} = cexprs(Lb, Exp, St1),
-    {Ch,_Us3,St3} = cexprs(Lh, Exp, St2),
+cexpr(#itry{anno=A,args=La,vars=Vs0,body=Lb,evars=Evs,handler=Lh}, _As, St0) ->
+    %% No variables are exported from try/catch. Starting in OTP 24,
+    %% variables bound in the argument (the code between the 'try' and
+    %% the 'of' keywords) are exported to the body (the code following
+    %% the 'of' keyword).
+    AsExp = intersection(new_in_any(La), used_in_any(Lb)),
+    {Ca,_Us1,St1} = cexprs(La, AsExp, St0),
+    {Cb,_Us2,St2} = cexprs(Lb, [], St1),
+    {Ch,_Us3,St3} = cexprs(Lh, [], St2),
+    Vs = Vs0 ++ [#c_var{name=V} || V <- AsExp],
     {#c_try{anno=A#a.anno,arg=Ca,vars=Vs,body=Cb,evars=Evs,handler=Ch},
-     Exp,A#a.us,St3};
+     [],A#a.us,St3};
 cexpr(#icatch{anno=A,body=Les}, _As, St0) ->
     {Ces,_Us1,St1} = cexprs(Les, [], St0),	%Never export!
     {#c_catch{body=Ces},[],A#a.us,St1};
diff --git a/lib/compiler/test/trycatch_SUITE.erl b/lib/compiler/test/trycatch_SUITE.erl
index 148969a4d1..630f96349b 100644
--- a/lib/compiler/test/trycatch_SUITE.erl
+++ b/lib/compiler/test/trycatch_SUITE.erl
@@ -29,6 +29,7 @@
 	 hockey/1,handle_info/1,catch_in_catch/1,grab_bag/1,
          stacktrace/1,nested_stacktrace/1,raise/1,
          no_return_in_try_block/1,
+         expression_export/1,
          coverage/1]).
 
 -include_lib("common_test/include/ct.hrl").
@@ -46,7 +47,8 @@ groups() ->
        bool,plain_catch_coverage,andalso_orelse,get_in_try,
        hockey,handle_info,catch_in_catch,grab_bag,
        stacktrace,nested_stacktrace,raise,
-       no_return_in_try_block,coverage]}].
+       no_return_in_try_block,expression_export,
+       coverage]}].
 
 
 init_per_suite(Config) ->
@@ -1383,6 +1385,75 @@ no_return_in_try_block_1(H) ->
 
 no_return() -> throw(no_return).
 
+expression_export(_Config) ->
+    42 = expr_export_1(),
+    42 = expr_export_2(),
+
+    42 = expr_export_3(fun() -> bar end),
+    beer = expr_export_3(fun() -> pub end),
+    {error,failed} = expr_export_3(fun() -> error(failed) end),
+    is_42 = expr_export_3(fun() -> 42 end),
+    no_good = expr_export_3(fun() -> bad end),
+
+    <<>> = expr_export_4(<<1:32>>),
+    <<"abcd">> = expr_export_4(<<2:32,"abcd">>),
+    no_match = expr_export_4(<<0:32>>),
+    no_match = expr_export_4(<<777:32>>),
+
+    {1,2,3} = expr_export_5(),
+    ok.
+
+expr_export_1() ->
+    try Bar = 42 of
+        _ -> Bar
+    after
+        ok
+    end.
+
+expr_export_2() ->
+    try Bar = 42 of
+        _ -> Bar
+    catch
+        _:_ ->
+            error
+    end.
+
+expr_export_3(F) ->
+    try
+        Bar = 42,
+        F()
+    of
+        bar -> Bar;
+        pub -> beer;
+        Bar -> is_42;
+        _ -> no_good
+    catch
+        error:Reason ->
+            {error,Reason}
+    end.
+
+expr_export_4(Bin) ->
+    try
+        SzSz = id(32),
+        Bin
+    of
+        <<Sz:SzSz,Tail:(4*Sz-4)/binary>> -> Tail;
+        <<_/binary>> -> no_match
+    after
+        ok
+    end.
+
+expr_export_5() ->
+    try
+        X = 1,
+        Z = 3,
+        Y = 2
+    of
+        2 -> {X,Y,Z}
+    after
+        ok
+    end.
+
 coverage(_Config) ->
     {'EXIT',{{badfun,true},[_|_]}} = (catch coverage_1()),
     ok.
diff --git a/lib/stdlib/src/erl_lint.erl b/lib/stdlib/src/erl_lint.erl
index 886988532f..fe3f1e33a8 100644
--- a/lib/stdlib/src/erl_lint.erl
+++ b/lib/stdlib/src/erl_lint.erl
@@ -2520,14 +2520,14 @@ expr({call,Line,F,As}, Vt, St0) ->
     St = warn_invalid_call(Line,F,St0),
     expr_list([F|As], Vt, St);                  %They see the same variables
 expr({'try',Line,Es,Scs,Ccs,As}, Vt, St0) ->
-    %% Currently, we don't allow any exports because later
-    %% passes cannot handle exports in combination with 'after'.
+    %% The only exports we allow are from the try expressions to the
+    %% success clauses.
     {Evt0,St1} = exprs(Es, Vt, St0),
     TryLine = {'try',Line},
     Uvt = vtunsafe(TryLine, Evt0, Vt),
-    Evt1 = vtupdate(Uvt, Evt0),
     {Sccs,St2} = try_clauses(Scs, Ccs, TryLine,
-                             vtupdate(Evt1, Vt), St1),
+                             vtupdate(Evt0, Vt), Uvt, St1),
+    Evt1 = vtupdate(Uvt, Evt0),
     Rvt0 = Sccs,
     Rvt1 = vtupdate(vtunsafe(TryLine, Rvt0, Vt), Rvt0),
     Evt2 = vtmerge(Evt1, Rvt1),
@@ -3333,10 +3333,10 @@ is_module_dialyzer_option(Option) ->
 %% try_catch_clauses(Scs, Ccs, In, ImportVarTable, State) ->
 %%      {UpdVt,State}.
 
-try_clauses(Scs, Ccs, In, Vt, St0) ->
+try_clauses(Scs, Ccs, In, Vt, Uvt, St0) ->
     {Csvt0,St1} = icrt_clauses(Scs, Vt, St0),
     St2 = St1#lint{in_try_head=true},
-    {Csvt1,St3} = icrt_clauses(Ccs, Vt, St2),
+    {Csvt1,St3} = icrt_clauses(Ccs, vtupdate(Uvt, Vt), St2),
     Csvt = Csvt0 ++ Csvt1,
     UpdVt = icrt_export(Csvt, Vt, In, St3),
     {UpdVt,St3#lint{in_try_head=false}}.
diff --git a/lib/stdlib/test/erl_lint_SUITE.erl b/lib/stdlib/test/erl_lint_SUITE.erl
index aa941e61b6..20f8407f85 100644
--- a/lib/stdlib/test/erl_lint_SUITE.erl
+++ b/lib/stdlib/test/erl_lint_SUITE.erl
@@ -1216,7 +1216,6 @@ unsafe_vars_try(Config) when is_list(Config) ->
 	   [],
 	   {errors,[{5,erl_lint,{unsafe_var,'R',{'try',3}}},
 		    {7,erl_lint,{unsafe_var,'Rc',{'try',3}}},
-		    {11,erl_lint,{unsafe_var,'R',{'try',10}}},
 		    {13,erl_lint,{unbound_var,'RR'}},
 		    {13,erl_lint,{unbound_var,'Ro'}},
 		    {13,erl_lint,{unsafe_var,'R',{'try',10}}},
@@ -1225,7 +1224,6 @@ unsafe_vars_try(Config) when is_list(Config) ->
 		    {15,erl_lint,{unsafe_var,'R',{'try',10}}},
 		    {15,erl_lint,{unsafe_var,'RR',{'try',10}}},
 		    {15,erl_lint,{unsafe_var,'Ro',{'try',10}}},
-		    {19,erl_lint,{unsafe_var,'R',{'try',18}}},
 		    {21,erl_lint,{unbound_var,'RR'}},
 		    {21,erl_lint,{unsafe_var,'R',{'try',18}}},
 		    {23,erl_lint,{unsafe_var,'Class',{'try',18}}},
@@ -1251,8 +1249,7 @@ unsafe_vars_try(Config) when is_list(Config) ->
                 {X,Try,R,RR,Ro,Rc,Ra,Class,Data}.
            ">>,
 	   [],
-	   {errors,[{4,erl_lint,{unsafe_var,'R',{'try',3}}},
-		    {6,erl_lint,{unbound_var,'RR'}},
+	   {errors,[{6,erl_lint,{unbound_var,'RR'}},
 		    {6,erl_lint,{unbound_var,'Ro'}},
 		    {6,erl_lint,{unsafe_var,'R',{'try',3}}},
 		    {8,erl_lint,{unsafe_var,'Class',{'try',3}}},
-- 
2.26.2

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File 2161-Allow-variables-bound-in-try-to-be-used-in-of-clause.patch of Package erlang (Revision 02775a1e4b9808dffc0e5f09fec6e4ec)

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