The first whitelist was too broad. ConstFetch, ClassConstFetch and the
base Node\Scalar type all admit expressions PHP must still evaluate, so
count([UNDEFINED_COUNT_LITERAL]), count([KnownClass::MISSING]) and
count(["{$object->property}"]) folded to 1, dropping two Errors and a
__get() call. The defined-variable check was not a purity proof either:
hasVar() only reports a compiler slot, not that the variable is still
initialized on every path after unset().
Narrow the fold to items whose evaluation cannot be observed:
- literal Int_, Float_ and String_ (an interpolated string is a distinct
InterpolatedString node, so String_ already excludes it);
- the language constants true, false and null only;
- unary plus/minus over a literal int or float;
- recursively safe nested arrays.
Variables, general constant and class constant fetches, interpolated
strings and every other expression stay on the runtime path, and
by-reference items are now rejected explicitly alongside keys and
unpacking.
Cover the three reported cases plus a by-reference item, a plain
variable read and a defined class constant in both the fold-decision
test and the PHPT.
doFoldCountLiteral replaced `count([...])` with the number of AST items
and dropped the array literal entirely. That is only correct when the
item count equals the runtime element count and no element carries an
observable effect. Three common shapes break both assumptions:
count([bump(), bump()]); // folded to 2, bump() never ran
count(['a' => 1, 'a' => 2]); // folded to 2, PHP counts 1
count([...$rest, 9]); // folded to 2, PHP counts 6
The spread case is the most damaging: it silently yields a wrong number
in ordinary code that compiles without any diagnostic.
The fold now applies only when every item is unkeyed, is not a spread,
and holds an expression whose evaluation cannot be observed - a scalar,
a constant fetch, a unary sign over either, a nested literal that is
itself foldable, or a variable already known to be defined. An undefined
variable still reaches the dynamic path so it reports the same
diagnostic as PHP. Everything else keeps the runtime php::fn::count()
call, so `count([1, 2, 3])` and friends still fold as before.
Covered by tests/compiler/array/count-literal-fold.phpt for the runtime
semantics and by CountLiteralFoldTest for the fold/no-fold decision in
the generated C++.
韩天峰
Giandonn