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Make trait constants behave like interface constants
Summary:
Trait constants were added to the language recently to obviate a workaround where traits themselves could not declare constants, but could bring in constants via interfaces. However, the semantics on conflict were to drop the conflicting constant; this is in contrast to interface conflicts, where you get a fatal at class loading time.

```
class A {
  const int X = 3;
}
interface I {
  const string X = "hello";
}

class C extends A implements I {} // Fatal runtime error

trait TI implements I {}
class D extends A { use TI; } // no fatal

// by extension
trait T { const bool X = false; }
class E extends A { use T; } // also no fatal
```
This flag allows the above cases to fatal, and it also fixes the behavior of defaults + makes HHVM align with Hack on member resolution order.

```
abstract class A {
  abstract const type T = arraykey;
}
trait T {
  const type T = int;
}
class C extends A { use T; } // C::T = int, was arraykey previously.
```
Equivalently, coeffect unsoundness given trait conflicts is resolved
```
abstract class A {
  abstract const ctx C = [];
}
trait T {
  const ctx C = [defaults];
  public function f()[this::C]: void {
    echo "impure";
  }
}
class C extends A { use T; } // runtime used to think (new C())->f() is pure, now it's correctly defaults.
```

The flag also changes HHBBC to insert trait constants before inserting locally declared constants of a class, which resolves a bug with printing the conflict error message and a static analysis failure where the trait constant was expecting to conflict with a shallowly declared constant (see trait_slot_conflict_repo.php).

Reviewed By: oulgen

Differential Revision: D28887745

fbshipit-source-id: a698e1818925ba17c2608ce34d50dc1400cfabd0
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vassilmladenov authored and facebook-github-bot committed Jun 15, 2021
1 parent bed8173 commit 94a20dc
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Showing 24 changed files with 225 additions and 39 deletions.
2 changes: 2 additions & 0 deletions hphp/compiler/analysis/emitter.cpp
Expand Up @@ -183,6 +183,8 @@ RepoGlobalData getGlobalData() {
RuntimeOption::EvalNoticeOnCoerceForStrConcat;
gd.NoticeOnCoerceForBitOp =
RuntimeOption::EvalNoticeOnCoerceForBitOp;
gd.TraitConstantInterfaceBehavior =
RuntimeOption::EvalTraitConstantInterfaceBehavior;

for (auto const& elm : RuntimeOption::ConstantFunctions) {
auto const s = internal_serialize(tvAsCVarRef(elm.second));
Expand Down
49 changes: 35 additions & 14 deletions hphp/hhbbc/index.cpp
Expand Up @@ -1708,19 +1708,24 @@ bool build_class_constants(ClassInfo* cinfo, ClsPreResolveUpdates& updates) {
}
}

// Constants from traits silently lose
if (fromTrait) {
removeNoOverride(cns);
return true;
if (!RO::EvalTraitConstantInterfaceBehavior) {
// Constants from traits silently lose
if (fromTrait) {
removeNoOverride(cns);
return true;
}
}

if ((cns->cls->attrs & (AttrInterface)) && existing->isAbstract) {
if ((cns->cls->attrs & AttrInterface ||
(RO::EvalTraitConstantInterfaceBehavior && (cns->cls->attrs & AttrTrait))) &&
existing->isAbstract) {
// because existing has val, this covers the case where it is abstract with default
// allow incoming to win
} else {
// A constant from an interface or from an included enum collides
// with an existing constant.
if (cns->cls->attrs & (AttrInterface | AttrEnum | AttrEnumClass)) {
if (cns->cls->attrs & (AttrInterface | AttrEnum | AttrEnumClass) ||
(RO::EvalTraitConstantInterfaceBehavior && (cns->cls->attrs & AttrTrait))) {
ITRACE(
2,
"build_class_constants failed for `{}' because "
Expand Down Expand Up @@ -1754,16 +1759,32 @@ bool build_class_constants(ClassInfo* cinfo, ClsPreResolveUpdates& updates) {
}
}

for (uint32_t idx = 0; idx < cinfo->cls->constants.size(); ++idx) {
auto const cns = ClassInfo::ConstIndex { cinfo->cls, idx };
if (cinfo->cls->attrs & AttrTrait) removeNoOverride(cns);
if (!add(cns, false)) return false;
}
auto const addShallowConstants = [&]() {
for (uint32_t idx = 0; idx < cinfo->cls->constants.size(); ++idx) {
auto const cns = ClassInfo::ConstIndex { cinfo->cls, idx };
if (cinfo->cls->attrs & AttrTrait) removeNoOverride(cns);
if (!add(cns, false)) return false;
}
return true;
};

for (auto const trait : cinfo->usedTraits) {
for (auto const& cns : trait->clsConstants) {
if (!add(cns.second, true)) return false;
auto const addTraitConstants = [&]() {
for (auto const trait : cinfo->usedTraits) {
for (auto const& cns : trait->clsConstants) {
if (!add(cns.second, true)) return false;
}
}
return true;
};

if (RO::EvalTraitConstantInterfaceBehavior) {
// trait constants must be inserted before constants shallowly declared on the class
// to match the interface semantics
if (!addTraitConstants()) return false;
if (!addShallowConstants()) return false;
} else {
if (!addShallowConstants()) return false;
if (!addTraitConstants()) return false;
}

for (auto const ienum : cinfo->includedEnums) {
Expand Down
3 changes: 3 additions & 0 deletions hphp/hhbbc/main.cpp
Expand Up @@ -339,6 +339,8 @@ RepoGlobalData get_global_data() {
RuntimeOption::EvalNoticeOnCoerceForStrConcat;
gd.NoticeOnCoerceForBitOp =
RuntimeOption::EvalNoticeOnCoerceForBitOp;
gd.TraitConstantInterfaceBehavior =
RuntimeOption::EvalTraitConstantInterfaceBehavior;

for (auto const& elm : RuntimeOption::ConstantFunctions) {
auto const s = internal_serialize(tvAsCVarRef(elm.second));
Expand Down Expand Up @@ -524,6 +526,7 @@ int main(int argc, char** argv) try {
RO::EvalHackArrDVArrs = true; // TODO(kshaunak): Clean it up.
RO::EvalArrayProvenance = false; // TODO(kshaunak): Clean it up.
RO::EvalEnforceGenericsUB = gd.HardGenericsUB ? 2 : 1;
RO::EvalTraitConstantInterfaceBehavior = gd.TraitConstantInterfaceBehavior;

if (print_bytecode_stats_and_exit) {
print_repo_bytecode_stats();
Expand Down
1 change: 1 addition & 0 deletions hphp/runtime/base/runtime-option.h
Expand Up @@ -1417,6 +1417,7 @@ struct RuntimeOption {
F(bool, EnableAbstractContextConstants, true) \
F(bool, TypeconstAbstractDefaultReflectionIsAbstract, false) \
F(bool, AbstractContextConstantUninitAccess, false) \
F(bool, TraitConstantInterfaceBehavior, false) \
/* */

private:
Expand Down
1 change: 1 addition & 0 deletions hphp/runtime/base/unit-cache.cpp
Expand Up @@ -1365,6 +1365,7 @@ std::string mangleUnitSha1(const std::string& fileSha1,
+ (RuntimeOption::EvalFoldLazyClassKeys ? '1' : '0')
+ (RuntimeOption::EvalHackCompilerUseCompilerPool ? '1' : '0')
+ (RuntimeOption::EvalEnableAbstractContextConstants ? '1': '0')
+ (RuntimeOption::EvalTraitConstantInterfaceBehavior ? '1' : '0')
+ RuntimeOption::EvalUnitCacheBreaker + '\0'
+ CoeffectsConfig::mangle()
+ opts.cacheKeySha1().toString()
Expand Down
68 changes: 47 additions & 21 deletions hphp/runtime/vm/class.cpp
Expand Up @@ -2281,28 +2281,54 @@ void Class::importTraitConsts(ConstMap::Builder& builder) {
return;
}

// Constants in interfaces implemented by traits don't fatal with constants
// in declInterfaces
if (isFromInterface) { return; }

// Type and Context constants in interfaces can be overriden.
if (tConst.kind() == ConstModifiers::Kind::Type ||
tConst.kind() == ConstModifiers::Kind::Context) {
return;
}
if (existingConst.cls != tConst.cls) {
if (RO::EvalTraitConstantInterfaceBehavior) {
if (existingConst.isAbstract()) {
// the case where the incoming constant is abstract without a default is covered above
// there are two remaining cases:
// - the incoming constant is abstract with a default
// - the incoming constant is concrete
// In both situations, the incoming constant should win, and separate bookkeeping will
// cover situations where there are multiple competing defaults.
existingConst.cls = tConst.cls;
existingConst.val = tConst.val;
return;
} else { // existing is concrete
// the existing constant will win over any incoming abstracts and retain a fatal when two
// concrete constants collide
if (!tConst.isAbstract() && existingConst.cls != tConst.cls) {
raise_error("%s cannot inherit the %s %s from %s, because "
"it was previously inherited from %s",
m_preClass->name()->data(),
ConstModifiers::show(tConst.kind()),
tConst.name->data(),
tConst.cls->name()->data(),
existingConst.cls->name()->data());
}
}
} else {
// Constants in interfaces implemented by traits don't fatal with constants
// in declInterfaces
if (isFromInterface) { return; }

// Constants in traits conflict with constants in declared interfaces
if (existingConst.cls->attrs() & AttrInterface) {
for (auto const& interface : m_declInterfaces) {
auto iface = existingConst.cls;
if (interface.get() == iface) {
raise_error("%s cannot inherit the %s %s, because "
"it was previously inherited from %s",
m_preClass->name()->data(),
ConstModifiers::show(tConst.kind()),
tConst.name->data(),
existingConst.cls->name()->data());
// Type and Context constants in interfaces can be overriden.
if (tConst.kind() == ConstModifiers::Kind::Type ||
tConst.kind() == ConstModifiers::Kind::Context) {
return;
}
if (existingConst.cls != tConst.cls) {

// Constants in traits conflict with constants in declared interfaces
if (existingConst.cls->attrs() & AttrInterface) {
for (auto const& interface : m_declInterfaces) {
auto iface = existingConst.cls;
if (interface.get() == iface) {
raise_error("%s cannot inherit the %s %s, because "
"it was previously inherited from %s",
m_preClass->name()->data(),
ConstModifiers::show(tConst.kind()),
tConst.name->data(),
existingConst.cls->name()->data());
}
}
}
}
Expand Down
3 changes: 2 additions & 1 deletion hphp/runtime/vm/repo-global-data.cpp
Expand Up @@ -47,6 +47,7 @@ void RepoGlobalData::load(bool loadConstantFuncs) const {
RO::EvalNoticeOnCoerceForStrConcat = NoticeOnCoerceForStrConcat;
RO::EvalNoticeOnCoerceForBitOp = NoticeOnCoerceForBitOp;
RO::EvalHackArrDVArrs = true; // TODO(kshaunak): Clean up.
RO::EvalTraitConstantInterfaceBehavior = TraitConstantInterfaceBehavior;

if (HardGenericsUB) RO::EvalEnforceGenericsUB = 2;

Expand Down Expand Up @@ -105,7 +106,7 @@ std::string show(const RepoGlobalData& gd) {
SHOW(StrictArrayFillKeys);
SHOW(NoticeOnCoerceForStrConcat);
SHOW(NoticeOnCoerceForBitOp);
SHOW(TypeconstInterfaceInheritanceDefaults);
SHOW(TraitConstantInterfaceBehavior);
#undef SHOW
return out;
}
Expand Down
6 changes: 3 additions & 3 deletions hphp/runtime/vm/repo-global-data.h
Expand Up @@ -161,8 +161,8 @@ struct RepoGlobalData {
/* Whether implicit coercions for bit ops trigger logs/exceptions */
int32_t NoticeOnCoerceForBitOp = 0;

/* New behavior for inheritance of abstract type constants with defaults */
bool TypeconstInterfaceInheritanceDefaults = false;
/* Constants from traits behave like constants from interfaces (error on conflict) */
bool TraitConstantInterfaceBehavior = false;

/*
* The Hack.Lang.StrictArrayFillKeys option the repo was compiled with.
Expand Down Expand Up @@ -215,7 +215,7 @@ struct RepoGlobalData {
(StrictArrayFillKeys)
(NoticeOnCoerceForStrConcat)
(NoticeOnCoerceForBitOp)
(TypeconstInterfaceInheritanceDefaults)
(TraitConstantInterfaceBehavior)
(ConstantFunctions)
;
}
Expand Down
1 change: 1 addition & 0 deletions hphp/test/slow/constants/config.ini
@@ -1,3 +1,4 @@
hhvm.enable_abstract_context_constants=1
hhvm.typeconst_abstract_default_reflection_is_abstract=1
hhvm.abstract_context_constant_uninit_access=1
hhvm.trait_constant_interface_behavior=1
1 change: 1 addition & 0 deletions hphp/test/slow/constants/hphp_config.ini
@@ -1,3 +1,4 @@
hhvm.enable_abstract_context_constants=1
hhvm.typeconst_abstract_default_reflection_is_abstract=1
hhvm.abstract_context_constant_uninit_access=1
hhvm.trait_constant_interface_behavior=1
17 changes: 17 additions & 0 deletions hphp/test/slow/constants/inherited_concrete_wins_class2.php
@@ -0,0 +1,17 @@
<?hh

abstract class A {
const type T = float;
}
trait Tr {
abstract const type T = int;
}
class C extends A {
use Tr;
}

<<__EntryPoint>>
function main(): void {
// expecting TypeStructureKind::OF_FLOAT = 3
var_dump(type_structure(C::class, "T"));
}
@@ -0,0 +1,4 @@
dict(1) {
["kind"]=>
int(3)
}
17 changes: 17 additions & 0 deletions hphp/test/slow/constants/inherited_concrete_wins_trait.php
@@ -0,0 +1,17 @@
<?hh

abstract class A {
abstract const type T = int;
}
trait Tr {
const type T = string;
}
class C extends A {
use Tr;
}

<<__EntryPoint>>
function main(): void {
// expecting TypeStructureKind::OF_STRING = 4
var_dump(type_structure(C::class, "T"));
}
@@ -0,0 +1,4 @@
dict(1) {
["kind"]=>
int(4)
}
13 changes: 13 additions & 0 deletions hphp/test/slow/constants/trait_constant_conflict.php
@@ -0,0 +1,13 @@
<?hh

class C {
const int X = 3;
}

trait T {
const string X = "hello";
}

class D extends C {
use T;
}
@@ -0,0 +1 @@
Fatal error: D cannot inherit the constant X from T, because it was previously inherited from C in %s/test/slow/constants/trait_constant_conflict.php on line 11
15 changes: 15 additions & 0 deletions hphp/test/slow/constants/trait_interface_equivalence.php
@@ -0,0 +1,15 @@
<?hh

interface I1 {
const type T = int;
}

trait T2 {
const type T = string;
}

// behavior should be equivalent to if T2 was `interface I2`
// and the declaration was `class C implements I1, I2`
class C implements I1 {
use T2;
}
@@ -0,0 +1 @@
Fatal error: C cannot inherit the type constant T from T2, because it was previously inherited from I1 in %s/test/slow/constants/trait_interface_equivalence.php on line 13
18 changes: 18 additions & 0 deletions hphp/test/slow/constants/trait_slot_conflict_repo.php
@@ -0,0 +1,18 @@
<?hh

interface IA {}

interface ITr {
const type T = int;
}
trait Tr implements ITr {}

class C implements IA {
use Tr;
const type T = int;
}

<<__EntryPoint>>
function main(): void {
echo "main";
}
2 changes: 2 additions & 0 deletions hphp/test/slow/constants/trait_slot_conflict_repo.php.expect
@@ -0,0 +1,2 @@
main

13 changes: 13 additions & 0 deletions hphp/test/slow/constants/trait_type_constant_conflict.php
@@ -0,0 +1,13 @@
<?hh

class C {
const type Ty = int;
}

trait T {
const type Ty = string;
}

class D extends C {
use T;
}
@@ -0,0 +1 @@
Fatal error: D cannot inherit the type constant Ty from %rT|D%r, because it was previously inherited from C in %s/test/slow/constants/trait_type_constant_conflict.php on line 11
22 changes: 22 additions & 0 deletions hphp/test/slow/constants/trait_unsoundness_example.php
@@ -0,0 +1,22 @@
<?hh

abstract class A {
const type T as arraykey = arraykey;
}

trait T {
const type T = int;
}

final class B extends A {
use T;
public static function cast(mixed $x): int {
return $x is this::T ? $x : 0;
}
}

<<__EntryPoint>>
function main(): void {
B::cast('break it'); // Error, string expected int
echo "No type hint violation";
}
@@ -0,0 +1 @@
No type hint violation

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