From e0e021b80033ddf04f805dbb451b0df2ec291cbd Mon Sep 17 00:00:00 2001
From: Richard Carlsson <richardc@klarna.com>
Date: Wed, 30 Mar 2016 16:29:58 +0200
Subject: Avoid dialyzer warnings for unreachable code in asserts

Dialyzer would warn about uses of the ?assert(BoolExpr) macro in assert.hrl
if the argument was known to be boolean-only.
---
 lib/stdlib/include/assert.hrl | 19 ++++++++++++-------
 1 file changed, 12 insertions(+), 7 deletions(-)

(limited to 'lib/stdlib')

diff --git a/lib/stdlib/include/assert.hrl b/lib/stdlib/include/assert.hrl
index 74fdbf57aa..9e5d4eb598 100644
--- a/lib/stdlib/include/assert.hrl
+++ b/lib/stdlib/include/assert.hrl
@@ -59,19 +59,22 @@
 -define(assert(BoolExpr),ok).
 -else.
 %% The assert macro is written the way it is so as not to cause warnings
-%% for clauses that cannot match, even if the expression is a constant.
+%% for clauses that cannot match, even if the expression is a constant or
+%% is known to be boolean-only.
 -define(assert(BoolExpr),
         begin
         ((fun () ->
+            __T = is_process_alive(self()),  % cheap source of truth
             case (BoolExpr) of
-                true -> ok;
+                __T -> ok;
                 __V -> erlang:error({assert,
                                      [{module, ?MODULE},
                                       {line, ?LINE},
                                       {expression, (??BoolExpr)},
                                       {expected, true},
-                                      case __V of false -> {value, __V};
-                                          _ -> {not_boolean,__V}
+                                      case not __T of
+                                          __V -> {value, false};
+                                          _ -> {not_boolean, __V}
                                       end]})
             end
           end)())
@@ -85,15 +88,17 @@
 -define(assertNot(BoolExpr),
         begin
         ((fun () ->
+            __F = not is_process_alive(self()),
             case (BoolExpr) of
-                false -> ok;
+                __F -> ok;
                 __V -> erlang:error({assert,
                                      [{module, ?MODULE},
                                       {line, ?LINE},
                                       {expression, (??BoolExpr)},
                                       {expected, false},
-                                      case __V of true -> {value, __V};
-                                          _ -> {not_boolean,__V}
+                                      case not __F of
+                                          __V -> {value, true};
+                                          _ -> {not_boolean, __V}
                                       end]})
             end
           end)())
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