Deprecate Str\is_empty

[rob0rt]

Functions can't refine input types in Hack, meaning that if the argument to Str\is_empty is non-null, it won't get refined even if the function returns true. This means that the function is, effectively, not valuable, since checking for emptiness via === '' or a nullcheck is more explicit.

We've found this function in practice to confuse developers, who expect type refinement, so we may deprecate this function and suggest explicit equality checks instead.

[lexidor]

Under

HipHop VM 4.18.0-dev (rel)
Compiler: 1565235181_072085492
Repo schema: 444f82394cc9ef6e84315eb3ea7dde7db022c046

$ns = nullable_string();
if ($ns is nonnull && $ns !== '') { //!Str\is_empty()
  return $ns;
}

refines like it should.

[fredemmott]

diffs up to start migration at FB; need to figure out the best way to do this with HHAST to deal with cases like Str\is_empty($foo[$bar][$baz] ?? null)

At FB, I'm adding a PHPism_FIXME::isEmptyStringOrNull() static method and using that for the non-trivial cases