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The fallback to latin-1 encoding would not work if the invalid
UTF-8 characters occurred in a skipped branch in an -ifdef/-ifndef.
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Even if a binary key is written as a literal the compiler may
choose to make an expression. Emit a warning in those cases
and saying the case will not match.
This is a limitation in current implementation.
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Increases coverage.
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The default encoding for Erlang modules is now UTF-8, and the
compilation would fail if a module contained byte sequences that
are not valid UTF-8 sequences.
In a large project with say many hundreds of Erlang modules
with names of developers such as "Björn" or "Håkan" encoded in
latin-1, that could mean that many hundreds of files would need
to be modified just to get started testing OTP 17.
As a temporary measure to ease the transition, automatically
fall back to the latin-1 encoding with a warning for any module
that contains invalid byte sequences and for which no encoding
has been specified.
The intention is to remove this workaround in OTP 18 or 19.
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Boolean case expressions with redundant clauses could make the compiler
crash:
case X == 0 of
false -> no;
false -> no;
true -> yes
end.
Reported-by: Ulf Norell
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Without this, sys_core_fold could crash on non-matching clauses using maps
patterns.
Reported-by: Ulf Norell
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Case expressions such as:
case {Expr1,Expr} of
{V1,V2} -> ...
end
are already optimized to not actually build the tuple. Generalize
the optimization to avoid building any kind of composite term,
such as:
case {ok,[A,B]} of
{ok,[X,Y]} -> ...
end
We don't expect programmers to write such code directly, but
inlining can produce such code.
We need to be careful about the warnings we produce. If the case
expression is a literal, it is expected that no warnings should be
produced for clauses that don't match. We must make sure that we
continue to suppress those warnings.
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When compiling comprehensions with generators which are foldable to
'true', a misleading warning is emitted by sys_core_fold because a
clause resulting from the compilation of the comprehension to Core
Erlang is not marked as generated by the compiler.
An example of such a comprehension is [ true || true ].
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Run testcases in parallel will make the test suite run slightly
faster. Another reason for this change is that we want more testing
of parallel testcase support in common_test.
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In 3d0f4a3085f11389e5b22d10f96f0cbf08c9337f (an update to conform
with common_test), in all test_lib:recompile(?MODULE) calls, ?MODULE
was changed to the actual name of the module. That would cause
test_lib:recompile/1 to compile the module with the incorrect
compiler options in cloned modules such as record_no_opt_SUITE,
causing worse coverage.
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The compiler (sys_core_fold) tries to avoid constructing tuples
in case expressions. The following code:
c(A, B) ->
case {A,B} of
{ok,X} -> X;
{_,_} -> error
end.
will be rewritten so that no tuple is built. If a clause
requires a tuple to be built as in this code:
c(A, B) ->
case {A,B} of
{ok,X} -> X;
V -> V %The tuple will be built here
end.
the tuple will be built in the clause(s) in which it is needed.
If the value returned from the case is not used as in this code:
c(A, B) ->
case {A,B} of
V -> V %Warning: a term is constructed, but never used
end,
ok.
there will be an incorrect warning. Basically, what happens is
that the code is reduced to:
c(A, B) ->
{A,B}, %Warning: a term is constructed, but never used
ok.
and the optimizer sees that the {A,B} tuple can't possibly be used.
Eliminate the warning by adding a 'compiler_generated' annotation
to the tuple.
Reported-by: Kostis Sagonas
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* bg/compiler-suppress-result-ignored:
compiler tests: Eliminate "result of expression is ignored" warnings
Silence warnings for expressions that are assigned to "_"
OTP-8602 bg/compiler-suppress-result-ignored
It is now possible to suppress the warning in code such as
"list_to_integer(S), ok" by assigning the ignored value "_" like this: "_ =
list_to_integer(S), ok".
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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.
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