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authorBjörn Gustavsson <[email protected]>2010-04-15 10:18:53 +0200
committerBjörn Gustavsson <[email protected]>2010-04-15 16:41:50 +0200
commitc34ad2d537e41c9b31e240aa1e6fadd994115a16 (patch)
tree2cbe3141d13a1ac40fdfa7486eef89be053f3100 /lib/compiler/test
parentab47252a5f7d540d4119d38dffe69acca86d2a41 (diff)
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Silence warnings for expressions that are assigned to "_"
There is currently no zero-cost way to silence the warning "the result of the expression is ignored", which is issued for code such as: list_to_integer(S), ok Such code can be useful for assertions or input validation. Teach the compiler to silence the warning for expressions that are explicitly assigned to to the "_" variable, such as: _ = list_to_integer(S), ok Implement it by having the v3_core pass annotate calls in Core Erlang like this: let <_> = ( call 'erlang':'list_to_integer'(S) -| ['result_not_wanted'] ) in 'ok' and modifiy sys_core_fold to suppress the warning for any call having the annotation. We deliberately do not make it possible to silence the warnings for expressions like: {build,an,unnecessary,term}, ok or is_list(L), ok because we don't know of any real-world scenarios in which that would be useful.
Diffstat (limited to 'lib/compiler/test')
-rw-r--r--lib/compiler/test/match_SUITE.erl16
-rw-r--r--lib/compiler/test/warnings_SUITE.erl7
2 files changed, 20 insertions, 3 deletions
diff --git a/lib/compiler/test/match_SUITE.erl b/lib/compiler/test/match_SUITE.erl
index 20969c0b26..7d5669025c 100644
--- a/lib/compiler/test/match_SUITE.erl
+++ b/lib/compiler/test/match_SUITE.erl
@@ -21,14 +21,14 @@
-export([all/1,
pmatch/1,mixed/1,aliases/1,match_in_call/1,
untuplify/1,shortcut_boolean/1,letify_guard/1,
- selectify/1]).
+ selectify/1,underscore/1]).
-include("test_server.hrl").
all(suite) ->
test_lib:recompile(?MODULE),
[pmatch,mixed,aliases,match_in_call,untuplify,shortcut_boolean,
- letify_guard,selectify].
+ letify_guard,selectify,underscore].
pmatch(Config) when is_list(Config) ->
?line ok = doit(1),
@@ -352,4 +352,16 @@ sel_same_value2(V) when V =:= 42; V =:= 43 ->
sel_same_value2(_) ->
error.
+underscore(Config) when is_list(Config) ->
+ case Config of
+ [] ->
+ %% Assignment to _ at the end of a construct.
+ _ = length(Config);
+ [_|_] ->
+ %% Assignment to _ at the end of a construct.
+ _ = list_to_tuple(Config)
+ end,
+ _ = is_list(Config),
+ ok.
+
id(I) -> I.
diff --git a/lib/compiler/test/warnings_SUITE.erl b/lib/compiler/test/warnings_SUITE.erl
index 6e60ab88cb..8b98db54f2 100644
--- a/lib/compiler/test/warnings_SUITE.erl
+++ b/lib/compiler/test/warnings_SUITE.erl
@@ -375,7 +375,12 @@ effect(Config) when is_list(Config) ->
comp_op ->
X =:= 2;
cookie ->
- erlang:get_cookie()
+ erlang:get_cookie();
+ result_ignore ->
+ _ = list_to_integer(X);
+ warn_lc_4 ->
+ %% No warning because of assignment to _.
+ [_ = abs(Z) || Z <- [1,2,3]]
end,
ok.