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[Performance Hints] Implement check for existential any #84684

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[Performance Hints] Implement check for existential any #84684

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13a5c2d
[Performance Hints] Implement check for existential any
aviralg Oct 2, 2025
8ab27fc
Use `Type.findIf` instead of TypeVisitor to avoid missing parent type
aviralg Oct 6, 2025
cbfb79d
Move checks inline to make the test file more readable
aviralg Oct 6, 2025
52304ec
Replace all uses of "existential any" with "existential"
aviralg Oct 6, 2025
30c6b5f
Replace all uses of "Ignored value" with "Declaration"
aviralg Oct 6, 2025
d0ebe90
Move diagnostics to postWalk and make all checks consistent
aviralg Oct 6, 2025
75c1fad
Enforce consistent capitalization in diagnostic messages
aviralg Oct 6, 2025
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2 changes: 2 additions & 0 deletions include/swift/AST/DiagnosticEngine.h
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Original file line number Diff line number Diff line change
Expand Up @@ -48,6 +48,8 @@ namespace swift {
class FuncDecl;
class SourceManager;
class SourceFile;
class ParamDecl;
class AnyPattern;

/// Enumeration describing all of possible diagnostics.
///
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2 changes: 2 additions & 0 deletions include/swift/AST/DiagnosticGroups.def
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Original file line number Diff line number Diff line change
Expand Up @@ -82,6 +82,8 @@ GROUP(WeakMutability, "weak-mutability")
GROUP(PerformanceHints, "performance-hints")
GROUP(ReturnTypeImplicitCopy, "return-type-implicit-copy")
GROUP_LINK(PerformanceHints, ReturnTypeImplicitCopy)
GROUP(ExistentialAnyType, "existential-any-type")
GROUP_LINK(PerformanceHints, ExistentialAnyType)

#define UNDEFINE_DIAGNOSTIC_GROUPS_MACROS
#include "swift/AST/DefineDiagnosticGroupsMacros.h"
24 changes: 24 additions & 0 deletions include/swift/AST/DiagnosticsSema.def
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Expand Up @@ -8946,6 +8946,30 @@ GROUPED_WARNING(perf_hint_closure_returns_array,ReturnTypeImplicitCopy,DefaultIg
"Performance: closure returns a%select{ dictionary|n array}0, leading to implicit copies. "
"Consider using an 'inout' parameter instead.", (bool))

GROUPED_WARNING(perf_hint_param_expects_existential_any,ExistentialAnyType,DefaultIgnore,
"Performance: %0 expects existential any, leading to heap allocation, reference counting, "
"and dynamic dispatch. Consider using generic constraints or concrete types instead.",
(const ParamDecl*))
GROUPED_WARNING(perf_hint_func_returns_existential_any,ExistentialAnyType,DefaultIgnore,
"Performance: %0 returns existential any, leading to heap allocation, reference counting, "
"and dynamic dispatch. Consider using generic constraints or concrete types instead.",
(const FuncDecl*))
GROUPED_WARNING(perf_hint_closure_returns_existential_any,ExistentialAnyType,DefaultIgnore,
"Performance: closure returns existential any, leading to heap allocation, reference counting, "
"and dynamic dispatch. Consider using generic constraints or concrete types instead.", ())
GROUPED_WARNING(perf_hint_var_uses_existential_any,ExistentialAnyType,DefaultIgnore,
"Performance: %0 uses existential any, leading to heap allocation, reference counting, "
"and dynamic dispatch. Consider using generic constraints or concrete types instead.",
(const VarDecl *))
GROUPED_WARNING(perf_hint_any_pattern_uses_existential_any,ExistentialAnyType,DefaultIgnore,
"Performance: Ignored value uses existential any, leading to heap allocation, reference counting, "
"and dynamic dispatch. Consider using generic constraints or concrete types instead.",
())
GROUPED_WARNING(perf_hint_typealias_uses_existential_any,ExistentialAnyType,DefaultIgnore,
"Performance: %0 aliases existential any type, leading to heap allocation, reference counting, "
"and dynamic dispatch. Consider using generic constraints or concrete types instead.",
(const TypeAliasDecl *))

ERROR(unsafe_self_dependent_result_attr_on_invalid_decl,none,
"invalid use of @_unsafeSelfDependentResult", ())

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152 changes: 148 additions & 4 deletions lib/Sema/PerformanceHints.cpp
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Expand Up @@ -25,12 +25,27 @@
#include "swift/AST/Evaluator.h"
#include "swift/AST/Expr.h"
#include "swift/AST/TypeCheckRequests.h"
#include "swift/AST/TypeVisitor.h"

using namespace swift;

bool swift::performanceHintDiagnosticsEnabled(ASTContext &ctx) {
return !ctx.Diags.isIgnoredDiagnostic(diag::perf_hint_closure_returns_array.ID) ||
!ctx.Diags.isIgnoredDiagnostic(diag::perf_hint_function_returns_array.ID);
return !ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_closure_returns_array.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_function_returns_array.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_param_expects_existential_any.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_func_returns_existential_any.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_closure_returns_existential_any.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_var_uses_existential_any.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_any_pattern_uses_existential_any.ID) ||
!ctx.Diags.isIgnoredDiagnostic(
diag::perf_hint_typealias_uses_existential_any.ID);
}

namespace {
Expand All @@ -52,6 +67,88 @@ void checkImplicitCopyReturnType(const ClosureExpr *Closure,
}
}

class CheckExistentialAny : public TypeVisitor<CheckExistentialAny, bool> {
public:
static bool inType(Type type) {
return CheckExistentialAny().visit(type->getCanonicalType());
}

static void inFunctionReturnType(FuncDecl *FD, DiagnosticEngine &Diags) {
Type T = FD->getResultInterfaceType();

if (inType(T))
Diags.diagnose(FD, diag::perf_hint_func_returns_existential_any, FD);
}

static void inClosureReturnType(ClosureExpr *CE, DiagnosticEngine &Diags) {
Type T = CE->getResultType();

if (inType(T))
Diags.diagnose(CE->getLoc(),
diag::perf_hint_closure_returns_existential_any);
}

static void inVariableType(const VarDecl *VD, DiagnosticEngine &Diags) {
Type T = VD->getInterfaceType();

if (inType(T))
Diags.diagnose(VD, diag::perf_hint_var_uses_existential_any, VD);
}

static void inPatternType(const AnyPattern *AP, DiagnosticEngine &Diags) {
Type T = AP->getType();

if (inType(T))
Diags.diagnose(AP->getLoc(),
diag::perf_hint_any_pattern_uses_existential_any);
}

static void inTypeAlias(const TypeAliasDecl *TAD, DiagnosticEngine &Diags) {
Type T = TAD->getUnderlyingType();

if (inType(T))
Diags.diagnose(TAD->getLoc(),
diag::perf_hint_typealias_uses_existential_any, TAD);
}

bool visitExistentialType(ExistentialType *ET) {
return true;
}

bool visitTupleType(TupleType *TT) {
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Using TypeVisitor for this is incorrect because you're going to miss a lot of cases. For example, a nominal type might have a parent, which you're not visiting at all:

struct Outer<T> {
  struct Inner {}
}

Outer<any P>.Inner

Please use Type.findIf() or Type.visit() instead.

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Fixed in #8ab27f Thanks for the example, added it as a test case.

for (const auto &element : TT->getElements()) {
if (visit(element.getType())) {
return true;
}
}
return false;
}

bool visitBoundGenericType(BoundGenericType *BGT) {
// Check generic arguments (e.g., Array<any Protocol>)
for (Type arg : BGT->getGenericArgs()) {
if (visit(arg)) {
return true;
}
}
return false;
}

bool visitFunctionType(FunctionType *FT) {
for (const auto &param : FT->getParams()) {
if (visit(param.getPlainType()->getCanonicalType())) {
return true;
}
}

return visit(FT->getResult()->getCanonicalType());
}

bool visitType(TypeBase *T) {
return false;
}
};

/// Produce performance hint diagnostics for a SourceFile.
class PerformanceHintDiagnosticWalker final : public ASTWalker {
ASTContext &Ctx;
Expand All @@ -64,16 +161,63 @@ class PerformanceHintDiagnosticWalker final : public ASTWalker {
SF->walk(Walker);
}

PreWalkResult<Pattern *> walkToPatternPre(Pattern *P) override {
if (P->isImplicit())
return Action::SkipNode(P);

if (const AnyPattern *AP = dyn_cast<AnyPattern>(P)) {
CheckExistentialAny::inPatternType(AP, Ctx.Diags);
}

return Action::Continue(P);
}

PreWalkResult<Expr *> walkToExprPre(Expr *E) override {
if (auto Closure = dyn_cast<ClosureExpr>(E))
if (E->isImplicit())
return Action::SkipNode(E);

if (const ClosureExpr* Closure = dyn_cast<ClosureExpr>(E)) {
checkImplicitCopyReturnType(Closure, Ctx.Diags);
}

return Action::Continue(E);
}

PostWalkResult<Expr *> walkToExprPost(Expr *E) override {
assert(
!E->isImplicit() &&
"Traversing implicit expressions is disabled in the pre-walk visitor");

if (auto Closure = dyn_cast<ClosureExpr>(E)) {
CheckExistentialAny::inClosureReturnType(Closure, Ctx.Diags);
}

return Action::Continue(E);
}

PreWalkAction walkToDeclPre(Decl *D) override {
if (auto *FD = dyn_cast<FuncDecl>(D))
if (D->isImplicit())
return Action::SkipNode();

if (const FuncDecl *FD = dyn_cast<FuncDecl>(D)) {
checkImplicitCopyReturnType(FD, Ctx.Diags);
} else if (const VarDecl *VD = dyn_cast<VarDecl>(D)) {
CheckExistentialAny::inVariableType(VD, Ctx.Diags);
} else if (const TypeAliasDecl *TAD = dyn_cast<TypeAliasDecl>(D)) {
CheckExistentialAny::inTypeAlias(TAD, Ctx.Diags);
}

return Action::Continue();
}

PostWalkAction walkToDeclPost(Decl *D) override {
assert(
!D->isImplicit() &&
"Traversing implicit declarations is disabled in the pre-walk visitor");

if (auto *FD = dyn_cast<FuncDecl>(D)) {
CheckExistentialAny::inFunctionReturnType(FD, Ctx.Diags);
}

return Action::Continue();
}
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