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Extend cpp-rule-preprocessor supported C++ rules #187

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81d131d
Extend cpp-rule-preprocessor supported C++ rules
joaotgouveia Jun 11, 2026
bcee7f9
Avoid relying on defaults for UsePreferredNames
joaotgouveia Jun 13, 2026
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1 change: 1 addition & 0 deletions cpp2rust/converter/mapper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@ clang::PrintingPolicy getPrintPolicy() {
policy.SuppressScope = false;
policy.FullyQualifiedName = true;
policy.SuppressUnwrittenScope = true;
policy.UsePreferredNames = true;
return policy;
}

Expand Down
160 changes: 152 additions & 8 deletions cpp2rust/cpp_rule_preprocessor.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -2,6 +2,7 @@
// Distributed under the MIT license that can be found in the LICENSE file.

#include <clang/AST/ASTContext.h>
#include <clang/AST/Attr.h>
#include <clang/AST/Decl.h>
#include <clang/AST/Expr.h>
#include <clang/AST/PrettyPrinter.h>
Expand Down Expand Up @@ -58,10 +59,15 @@ struct LookupInfo {
name = dm->getMember();
kind = LookupKind::CXXMethodName;
explicitArgs = dm->template_arguments();
} else if (const auto *um =
llvm::dyn_cast<clang::UnresolvedMemberExpr>(expr)) {
name = um->getMemberName();
kind = LookupKind::CXXMethodName;
explicitArgs = um->template_arguments();
} else if (const auto *dref =
llvm::dyn_cast<clang::DependentScopeDeclRefExpr>(expr)) {
clang::DeclarationName dname = dref->getDeclName();
if (name.getNameKind() ==
if (dname.getNameKind() ==
clang::DeclarationName::NameKind::CXXConstructorName) {
name = dname;
kind = LookupKind::CXXConstructorName;
Expand Down Expand Up @@ -260,7 +266,8 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
return spec;
}

if (result == clang::TemplateDeductionResult::SubstitutionFailure) {
if (result == clang::TemplateDeductionResult::SubstitutionFailure ||
result == clang::TemplateDeductionResult::ConstraintsNotSatisfied) {
if (const auto *deduced = info.takeCanonical()) {
clang::TemplateArgumentListInfo targsInfo;
for (const auto &arg : deduced->asArray()) {
Expand Down Expand Up @@ -292,7 +299,9 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
return ns;
}

clang::RecordDecl *createRecordDecl(llvm::StringRef name) {
clang::RecordDecl *
createRecordDecl(llvm::StringRef name,
clang::QualType base = clang::QualType()) {
bool owned = true;
bool dependent = false;
clang::CXXScopeSpec scope;
Expand All @@ -305,11 +314,135 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
clang::TypeResult(), false, false, clang::OffsetOfKind::Outside);
assert(decl.isUsable() && "Record decl creation failed");
auto *rdecl = decl.getAs<clang::RecordDecl>();

rdecl->startDefinition();
if (!base.isNull()) {
clang::CXXBaseSpecifier baseSpec(
clang::SourceRange(loc_, loc_), false, true, clang::AS_public,
sema_->Context.getTrivialTypeSourceInfo(base, loc_),
/*EllipsisLoc=*/clang::SourceLocation());
const clang::CXXBaseSpecifier *bases[] = {&baseSpec};
llvm::cast<clang::CXXRecordDecl>(rdecl)->setBases(bases, 1);
}
rdecl->completeDefinition();
return rdecl;
}

static clang::QualType getNTTPType(const clang::TemplateArgument &arg) {
switch (arg.getKind()) {
case clang::TemplateArgument::Integral:
return arg.getIntegralType();
case clang::TemplateArgument::Declaration:
return arg.getParamTypeForDecl();
case clang::TemplateArgument::NullPtr:
return arg.getNullPtrType();
case clang::TemplateArgument::StructuralValue:
return arg.getStructuralValueType();
default:
return clang::QualType();
}
}

clang::QualType createMirrorType(llvm::StringRef name, clang::QualType hint) {
clang::ASTContext &ctx = sema_->Context;
forceCompleteDefinition(hint);

const auto *hdecl = hint->getAsCXXRecordDecl();
assert(hdecl && "Failed resolving hint record declaration");
assert(hdecl->isCompleteDefinition() && "Incomplete hint");

const auto *hspec =
llvm::dyn_cast<clang::ClassTemplateSpecializationDecl>(hdecl);
if (!hspec) {
// if it is not a template specialization inheriting from it suffices
clang::RecordDecl *rdecl = createRecordDecl(name, hint);
return ctx.getTagType(clang::ElaboratedTypeKeyword::None,
rdecl->getQualifier(), rdecl, false);
}

auto *pattern = clang::CXXRecordDecl::Create(
ctx, clang::TagTypeKind::Struct, sema_->CurContext, loc_, loc_,
&ctx.Idents.get(name));

auto *htdecl = hspec->getSpecializedTemplate();
auto *mirror = clang::ClassTemplateDecl::Create(
ctx, sema_->CurContext, loc_,
clang::DeclarationName(&ctx.Idents.get(name)),
htdecl->getTemplateParameters(), pattern);
pattern->setDescribedClassTemplate(mirror);

clang::TemplateArgumentListInfo bargs(loc_, loc_);
for (const clang::TemplateArgument &arg :
htdecl->getTemplateParameters()->getInjectedTemplateArgs(ctx)) {
bargs.addArgument(
sema_->getTrivialTemplateArgumentLoc(arg, getNTTPType(arg), loc_));
}
clang::QualType base_t = sema_->CheckTemplateIdType(
clang::ElaboratedTypeKeyword::None, clang::TemplateName(htdecl), loc_,
bargs, sema_->getCurScope(), /*ForNestedNameSpecifier=*/false);
assert(!base_t.isNull() && "Failed building mirror base");

pattern->startDefinition();
clang::CXXBaseSpecifier base(clang::SourceRange(loc_, loc_), false, true,
clang::AS_public,
ctx.getTrivialTypeSourceInfo(base_t, loc_),
/*EllipsisLoc=*/clang::SourceLocation());
const clang::CXXBaseSpecifier *bases[] = {&base};
pattern->setBases(bases, 1);
pattern->completeDefinition();
sema_->CurContext->addDecl(mirror);

clang::TemplateArgumentListInfo args(loc_, loc_);
for (const clang::TemplateArgument &arg :
hspec->getTemplateArgs().asArray()) {
args.addArgument(
sema_->getTrivialTemplateArgumentLoc(arg, getNTTPType(arg), loc_));
}

clang::QualType spec = sema_->CheckTemplateIdType(
clang::ElaboratedTypeKeyword::None, clang::TemplateName(mirror), loc_,
args, sema_->getCurScope(), /*ForNestedNameSpecifier=*/false);
assert(!spec.isNull() && spec->getAsCXXRecordDecl());

// required to print Tn instead of Tn<arg1, arg2, ...>
clang::NamespaceDecl *ns = createNamespaceDecl();
auto *alias =
clang::TypeAliasDecl::Create(ctx, ns, loc_, loc_, &ctx.Idents.get(name),
ctx.getTrivialTypeSourceInfo(spec, loc_));
ns->addDecl(alias);

clang::QualType alias_t = ctx.getTypedefType(
clang::ElaboratedTypeKeyword::None, std::nullopt, alias);
spec->getAsCXXRecordDecl()->addAttr(
clang::PreferredNameAttr::CreateImplicit(
ctx, ctx.getTrivialTypeSourceInfo(alias_t, loc_)));

return ctx.getCanonicalType(spec);
}

clang::QualType
getDefaultArg(clang::TemplateDecl *decl,
const clang::TemplateTypeParmDecl *parm,
llvm::ArrayRef<clang::TemplateArgument> currentArgs) {
clang::QualType type = parm->getDefaultArgument().getArgument().getAsType();
if (!type->isDependentType()) {
return type;
}

clang::Sema::InstantiatingTemplate Inst(*sema_, loc_, decl);
assert(!Inst.isInvalid() && "Invalid instantiation context");

clang::MultiLevelTemplateArgumentList mtal;
mtal.setKind(clang::TemplateSubstitutionKind::Rewrite);
mtal.addOuterTemplateArguments(currentArgs);

clang::TypeSourceInfo *tsi =
sema_->SubstType(sema_->Context.getTrivialTypeSourceInfo(type), mtal,
loc_, clang::DeclarationName());
assert(tsi && "Template argument type instantiation failed");
return tsi->getType();
}

clang::VarDecl *createVarDecl(clang::QualType type, llvm::StringRef name,
clang::StorageClass sclass = clang::SC_None) {
clang::ASTContext &ctx = sema_->Context;
Expand Down Expand Up @@ -354,11 +487,19 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
createTemplateArguments(clang::TemplateDecl *decl,
llvm::SmallVectorImpl<clang::TemplateArgument> &out) {
for (clang::NamedDecl *param : *decl->getTemplateParameters()) {
if (llvm::isa<clang::TemplateTypeParmDecl>(param)) {
clang::RecordDecl *rdecl = createRecordDecl(param->getName());
clang::QualType type =
sema_->Context.getTagType(clang::ElaboratedTypeKeyword::None,
rdecl->getQualifier(), rdecl, false);
if (const auto *ttp =
llvm::dyn_cast<clang::TemplateTypeParmDecl>(param)) {
clang::QualType type;
if (ttp->hasDefaultArgument()) {
clang::QualType hint = getDefaultArg(decl, ttp, out);
assert(!hint.isNull() && "Failed retrieving type hint");
type = createMirrorType(param->getName(), hint);
} else {
clang::RecordDecl *rdecl = createRecordDecl(param->getName());
type = sema_->Context.getTagType(clang::ElaboratedTypeKeyword::None,
rdecl->getQualifier(), rdecl, false);
}
assert(!type.isNull() && "Template type argument creation failed");
out.emplace_back(type);
} else if (const auto *nttp =
llvm::dyn_cast<clang::NonTypeTemplateParmDecl>(param)) {
Expand Down Expand Up @@ -504,6 +645,7 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
clang::NamespaceDecl *ns = createNamespaceDecl();
clang::Sema::ContextRAII savedContext(*sema_, ns);
clang::FunctionDecl *rule = instantiateRuleDecl(decl);
assert(rule && "Rule instantiation failed");
llvm::ArrayRef<clang::ParmVarDecl *> parms = rule->parameters();
auto csk = lookup.name.getNameKind() ==
clang::DeclarationName::NameKind::CXXOperatorName
Expand Down Expand Up @@ -610,6 +752,7 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
clang::NamespaceDecl *ns = createNamespaceDecl();
clang::Sema::ContextRAII savedContext(*sema_, ns);
clang::FunctionDecl *rule = instantiateRuleDecl(decl);
assert(rule && "Rule instantiation failed");
clang::CXXRecordDecl *rdecl =
resolveCXXRecordDecl(rule->getParamDecl(0)->getType());
assert(rdecl && "Failed fetching record decl");
Expand All @@ -627,6 +770,7 @@ class Callback : public clang::ast_matchers::MatchFinder::MatchCallback {
clang::NamespaceDecl *ns = createNamespaceDecl();
clang::Sema::ContextRAII savedContext(*sema_, ns);
clang::FunctionDecl *rule = instantiateRuleDecl(decl);
assert(rule && "Rule instantiation failed");

clang::Expr *obj = createOpaqueValueExpr(
rule->getParamDecl(0)->getType().getNonReferenceType());
Expand Down
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