int lambdaUseValue(Expression *e, void *param)
{
switch (e->op)
{
case TOKcomma:
{ CommaExp *ce = (CommaExp *)e;
discardValue(ce->E1);
break;
}
default:
break;
}
return 0;
}
/***********************************
* The result of this expression will be discarded.
* Print error messages if the operation has no side effects (and hence is meaningless).
* Returns:
* true if expression has no side effects
*/
bool discardValue(Expression *e)
{
if (lambdaHasSideEffect(e)) // check side-effect shallowly
return false;
switch (e->op)
{
case TOKcast:
{
CastExp *ce = (CastExp *)e;
if (ce->to->equals(Type::tvoid))
{
/*
* Don't complain about an expression with no effect if it was cast to void
*/
return false;
}
break; // complain
}
case TOKerror:
return false;
case TOKvar:
{
VarDeclaration *v = ((VarExp *)e)->var->isVarDeclaration();
if (v && (v->storage_class & STCtemp))
{
// Bugzilla 5810: Don't complain about an internal generated variable.
return false;
}
break;
}
case TOKcall:
/* Issue 3882: */
if (global.params.warnings != DIAGNOSTICoff && !global.gag)
{
CallExp *ce = (CallExp *)e;
if (e->type->ty == Tvoid)
{
/* Don't complain about calling void-returning functions with no side-effect,
* because purity and nothrow are inferred, and because some of the
* runtime library depends on it. Needs more investigation.
*
* One possible solution is to restrict this message to only be called in hierarchies that
* never call assert (and or not called from inside unittest blocks)
*/
}
else if (ce->e1->type)
{
Type *t = ce->e1->type->toBasetype();
if (t->ty == Tdelegate)
t = ((TypeDelegate *)t)->next;
if (t->ty == Tfunction &&
(ce->f ? callSideEffectLevel(ce->f)
: callSideEffectLevel(ce->e1->type)) > 0)
{
const char *s;
if (ce->f)
s = ce->f->toPrettyChars();
else if (ce->e1->op == TOKstar)
{
// print 'fp' if ce->e1 is (*fp)
s = ((PtrExp *)ce->e1)->e1->toChars();
}
else
s = ce->e1->toChars();
e->warning("calling %s without side effects discards return value of type %s, prepend a cast(void) if intentional",
s, e->type->toChars());
}
}
}
return false;
case TOKscope:
e->error("%s has no effect", e->toChars());
return true;
case TOKandand:
{
AndAndExp *aae = (AndAndExp *)e;
return discardValue(aae->e2);
}
case TOKoror:
{
OrOrExp *ooe = (OrOrExp *)e;
return discardValue(ooe->e2);
}
case TOKquestion:
{
CondExp *ce = (CondExp *)e;
/* Bugzilla 6178 & 14089: Either CondExp::e1 or e2 may have
* redundant expression to make those types common. For example:
*
* struct S { this(int n); int v; alias v this; }
* S[int] aa;
* aa[1] = 0;
*
* The last assignment statement will be rewitten to:
*
* 1 in aa ? aa[1].value = 0 : (aa[1] = 0, aa[1].this(0)).value;
*
* The last DotVarExp is necessary to take assigned value.
*
* int value = (aa[1] = 0); // value = aa[1].value
*
* To avoid false error, discardValue() should be called only when
* the both tops of e1 and e2 have actually no side effects.
*/
if (!lambdaHasSideEffect(ce->e1) &&
!lambdaHasSideEffect(ce->e2))
{
return discardValue(ce->e1) |
discardValue(ce->e2);
}
return false;
}
case TOKcomma:
{
CommaExp *ce = (CommaExp *)e;
/* Check for compiler-generated code of the form auto __tmp, e, __tmp;
* In such cases, only check e for side effect (it's OK for __tmp to have
* no side effect).
* See Bugzilla 4231 for discussion
*/
CommaExp *firstComma = ce;
while (firstComma->e1->op == TOKcomma)
firstComma = (CommaExp *)firstComma->e1;
if (firstComma->e1->op == TOKdeclaration &&
ce->e2->op == TOKvar &&
((DeclarationExp *)firstComma->e1)->declaration == ((VarExp*)ce->e2)->var)
{
return false;
}
// Don't check e1 until we cast(void) the a,b code generation
//discardValue(ce->e1);
return discardValue(ce->e2);
}
case TOKtuple:
/* Pass without complaint if any of the tuple elements have side effects.
* Ideally any tuple elements with no side effects should raise an error,
* this needs more investigation as to what is the right thing to do.
*/
if (!hasSideEffect(e))
break;
return false;
default:
break;
}
e->error("%s has no effect in expression (%s)", Token::toChars(e->op), e->toChars());
return true;
}
/***********************************
* The result of this expression will be discarded.
* Complain if the operation has no side effects (and hence is meaningless).
*/
void discardValue(Expression *e)
{
if (hasSideEffect(e))
return;
switch (e->op)
{
case TOKcast:
{
CastExp *ce = (CastExp *)e;
if (ce->to->equals(Type::tvoid))
{
/*
* Don't complain about an expression with no effect if it was cast to void
*/
return;
}
break; // complain
}
case TOKerror:
return;
case TOKcall:
/* Issue 3882: */
if (global.params.warnings && !global.gag)
{
if (e->type->ty == Tvoid)
{
/* Don't complain about calling void-returning functions with no side-effect,
* because purity and nothrow are inferred, and because some of the
* runtime library depends on it. Needs more investigation.
*
* One possible solution is to restrict this message to only be called in hierarchies that
* never call assert (and or not called from inside unittest blocks)
*/
}
else
{
CallExp *ce = (CallExp *)e;
e->warning("Call to strictly pure function %s discards return value of type %s, prepend a cast(void) if intentional",
ce->f->toPrettyChars(),
e->type->toChars());
}
}
return;
case TOKimport:
e->error("%s has no effect", e->toChars());
return;
case TOKandand:
{
AndAndExp *aae = (AndAndExp *)e;
discardValue(aae->e2);
return;
}
case TOKoror:
{
OrOrExp *ooe = (OrOrExp *)e;
discardValue(ooe->e2);
return;
}
case TOKquestion:
{
CondExp *ce = (CondExp *)e;
discardValue(ce->e1);
discardValue(ce->e2);
return;
}
case TOKcomma:
{
CommaExp *ce = (CommaExp *)e;
/* Check for compiler-generated code of the form auto __tmp, e, __tmp;
* In such cases, only check e for side effect (it's OK for __tmp to have
* no side effect).
* See Bugzilla 4231 for discussion
*/
CommaExp* firstComma = ce;
while (firstComma->e1->op == TOKcomma)
firstComma = (CommaExp *)firstComma->e1;
if (firstComma->e1->op == TOKdeclaration &&
ce->e2->op == TOKvar &&
((DeclarationExp *)firstComma->e1)->declaration == ((VarExp*)ce->e2)->var)
{
return;
}
// Don't check e1 until we cast(void) the a,b code generation
//discardValue(ce->e1);
discardValue(ce->e2);
return;
}
case TOKtuple:
/* Pass without complaint if any of the tuple elements have side effects.
* Ideally any tuple elements with no side effects should raise an error,
* this needs more investigation as to what is the right thing to do.
*/
if (!hasSideEffect(e))
break;
return;
default:
break;
}
e->error("%s has no effect in expression (%s)", Token::toChars(e->op), e->toChars());
}
