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[clang] Implement evaluation context for checking template parameters
Instead of manually adding a note pointing to the relevant template parameter to every relevant error, which is very easy to miss, this patch adds a new instantiation context note, so that this can work using RAII magic. This fixes a bunch of places where these notes were missing, and is more future-proof. Some diagnostics are reworked to make better use of this note: - Errors about missing template arguments now refer to the parameter which is missing an argument. - Template Template parameter mismatches now refer to template parameters as parameters instead of arguments. It's likely this will add the note to some diagnostics where the parameter is not super relevant, but this can be reworked with time and the decrease in maintenance burden makes up for it. This bypasses the templight dumper for the new context entry, as the tests are very hard to update. This depends on #125453, which is needed to avoid losing the context note for errors occuring during template argument deduction.
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‎clang/docs/ReleaseNotes.rst

Lines changed: 10 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -149,6 +149,16 @@ Bug Fixes to C++ Support
149149
- Clang now prints the correct instantiation context for diagnostics suppressed
150150
by template argument deduction.
151151

152+
Improvements to C++ diagnostics
153+
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
154+
155+
- Clang now more consistently adds a note pointing to the relevant template
156+
parameter. Some diagnostics are reworded to better take advantage of this.
157+
- Template Template Parameter diagnostics now stop referring to template
158+
parameters as template arguments, in some circumstances, better hiding
159+
from the users template template parameter partial ordering arcana.
160+
161+
152162
Bug Fixes to AST Handling
153163
^^^^^^^^^^^^^^^^^^^^^^^^^
154164

‎clang/include/clang/Basic/DiagnosticSemaKinds.td

Lines changed: 7 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -5290,10 +5290,14 @@ def err_template_missing_args : Error<
52905290
"%select{class template|function template|variable template|alias template|"
52915291
"template template parameter|concept|template}0 %1 requires template "
52925292
"arguments">;
5293-
def err_template_arg_list_different_arity : Error<
5294-
"%select{too few|too many}0 template arguments for "
5293+
def err_template_param_missing_arg : Error<
5294+
"missing template argument for template parameter">;
5295+
def err_template_template_param_missing_param : Error<
5296+
"missing template parameter to bind to template template parameter">;
5297+
def err_template_too_many_args : Error<
5298+
"too many template arguments for "
52955299
"%select{class template|function template|variable template|alias template|"
5296-
"template template parameter|concept|template}1 %2">;
5300+
"template template parameter|concept|template}0 %1">;
52975301
def note_template_decl_here : Note<"template is declared here">;
52985302
def note_template_decl_external : Note<
52995303
"template declaration from hidden source: %0">;

‎clang/include/clang/Sema/Sema.h

Lines changed: 18 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -11781,7 +11781,7 @@ class Sema final : public SemaBase {
1178111781
bool *ConstraintsNotSatisfied = nullptr);
1178211782

1178311783
bool CheckTemplateTypeArgument(
11784-
TemplateTypeParmDecl *Param, TemplateArgumentLoc &Arg,
11784+
TemplateArgumentLoc &Arg,
1178511785
SmallVectorImpl<TemplateArgument> &SugaredConverted,
1178611786
SmallVectorImpl<TemplateArgument> &CanonicalConverted);
1178711787

@@ -11817,9 +11817,10 @@ class Sema final : public SemaBase {
1181711817
bool PartialOrdering,
1181811818
bool *StrictPackMatch);
1181911819

11820+
SmallString<128> toTerseString(const NamedDecl &D) const;
11821+
1182011822
void NoteTemplateLocation(const NamedDecl &Decl,
1182111823
std::optional<SourceRange> ParamRange = {});
11822-
void NoteTemplateParameterLocation(const NamedDecl &Decl);
1182311824

1182411825
/// Given a non-type template argument that refers to a
1182511826
/// declaration and the type of its corresponding non-type template
@@ -12821,6 +12822,9 @@ class Sema final : public SemaBase {
1282112822

1282212823
/// We are performing partial ordering for template template parameters.
1282312824
PartialOrderingTTP,
12825+
12826+
/// Checking a Template Parameter
12827+
CheckTemplateParameter,
1282412828
} Kind;
1282512829

1282612830
/// Was the enclosing context a non-instantiation SFINAE context?
@@ -13048,6 +13052,11 @@ class Sema final : public SemaBase {
1304813052
PartialOrderingTTP, TemplateDecl *PArg,
1304913053
SourceRange InstantiationRange = SourceRange());
1305013054

13055+
struct CheckTemplateParameter {};
13056+
/// \brief Note that we are checking a template parameter.
13057+
InstantiatingTemplate(Sema &SemaRef, CheckTemplateParameter,
13058+
NamedDecl *Param);
13059+
1305113060
/// Note that we have finished instantiating this template.
1305213061
void Clear();
1305313062

@@ -13081,6 +13090,13 @@ class Sema final : public SemaBase {
1308113090
InstantiatingTemplate &operator=(const InstantiatingTemplate &) = delete;
1308213091
};
1308313092

13093+
/// For any diagnostics which occur within its scope, adds a context note
13094+
/// pointing to the declaration of the template parameter.
13095+
struct CheckTemplateParameterRAII : InstantiatingTemplate {
13096+
CheckTemplateParameterRAII(Sema &S, NamedDecl *Param)
13097+
: InstantiatingTemplate(S, CheckTemplateParameter(), Param) {}
13098+
};
13099+
1308413100
bool SubstTemplateArgument(const TemplateArgumentLoc &Input,
1308513101
const MultiLevelTemplateArgumentList &TemplateArgs,
1308613102
TemplateArgumentLoc &Output,

‎clang/lib/Frontend/FrontendActions.cpp

Lines changed: 16 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -403,7 +403,8 @@ class DefaultTemplateInstCallback : public TemplateInstantiationCallback {
403403
}
404404

405405
private:
406-
static std::string toString(CodeSynthesisContext::SynthesisKind Kind) {
406+
static std::optional<std::string>
407+
toString(CodeSynthesisContext::SynthesisKind Kind) {
407408
switch (Kind) {
408409
case CodeSynthesisContext::TemplateInstantiation:
409410
return "TemplateInstantiation";
@@ -461,21 +462,25 @@ class DefaultTemplateInstCallback : public TemplateInstantiationCallback {
461462
return "TypeAliasTemplateInstantiation";
462463
case CodeSynthesisContext::PartialOrderingTTP:
463464
return "PartialOrderingTTP";
465+
case CodeSynthesisContext::CheckTemplateParameter:
466+
return std::nullopt;
464467
}
465-
return "";
468+
return std::nullopt;
466469
}
467470

468471
template <bool BeginInstantiation>
469472
static void displayTemplightEntry(llvm::raw_ostream &Out, const Sema &TheSema,
470473
const CodeSynthesisContext &Inst) {
471474
std::string YAML;
472475
{
476+
std::optional<TemplightEntry> Entry =
477+
getTemplightEntry<BeginInstantiation>(TheSema, Inst);
478+
if (!Entry)
479+
return;
473480
llvm::raw_string_ostream OS(YAML);
474481
llvm::yaml::Output YO(OS);
475-
TemplightEntry Entry =
476-
getTemplightEntry<BeginInstantiation>(TheSema, Inst);
477482
llvm::yaml::EmptyContext Context;
478-
llvm::yaml::yamlize(YO, Entry, true, Context);
483+
llvm::yaml::yamlize(YO, *Entry, true, Context);
479484
}
480485
Out << "---" << YAML << "\n";
481486
}
@@ -555,10 +560,13 @@ class DefaultTemplateInstCallback : public TemplateInstantiationCallback {
555560
}
556561

557562
template <bool BeginInstantiation>
558-
static TemplightEntry getTemplightEntry(const Sema &TheSema,
559-
const CodeSynthesisContext &Inst) {
563+
static std::optional<TemplightEntry>
564+
getTemplightEntry(const Sema &TheSema, const CodeSynthesisContext &Inst) {
560565
TemplightEntry Entry;
561-
Entry.Kind = toString(Inst.Kind);
566+
std::optional<std::string> Kind = toString(Inst.Kind);
567+
if (!Kind)
568+
return std::nullopt;
569+
Entry.Kind = *Kind;
562570
Entry.Event = BeginInstantiation ? "Begin" : "End";
563571
llvm::raw_string_ostream OS(Entry.Name);
564572
printEntryName(TheSema, Inst.Entity, OS);

‎clang/lib/Sema/SemaInit.cpp

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -7246,7 +7246,7 @@ static void CheckCXX98CompatAccessibleCopy(Sema &S,
72467246

72477247
void InitializationSequence::PrintInitLocationNote(Sema &S,
72487248
const InitializedEntity &Entity) {
7249-
if (Entity.isParamOrTemplateParamKind() && Entity.getDecl()) {
7249+
if (Entity.isParameterKind() && Entity.getDecl()) {
72507250
if (Entity.getDecl()->getLocation().isInvalid())
72517251
return;
72527252

@@ -7255,9 +7255,8 @@ void InitializationSequence::PrintInitLocationNote(Sema &S,
72557255
<< Entity.getDecl()->getDeclName();
72567256
else
72577257
S.Diag(Entity.getDecl()->getLocation(), diag::note_parameter_here);
7258-
}
7259-
else if (Entity.getKind() == InitializedEntity::EK_RelatedResult &&
7260-
Entity.getMethodDecl())
7258+
} else if (Entity.getKind() == InitializedEntity::EK_RelatedResult &&
7259+
Entity.getMethodDecl())
72617260
S.Diag(Entity.getMethodDecl()->getLocation(),
72627261
diag::note_method_return_type_change)
72637262
<< Entity.getMethodDecl()->getDeclName();

‎clang/lib/Sema/SemaLambda.cpp

Lines changed: 3 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1506,14 +1506,13 @@ void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
15061506
TemplateParameterList *TemplateParams =
15071507
getGenericLambdaTemplateParameterList(LSI, *this);
15081508
if (TemplateParams) {
1509-
for (const auto *TP : TemplateParams->asArray()) {
1509+
for (auto *TP : TemplateParams->asArray()) {
15101510
if (!TP->getIdentifier())
15111511
continue;
1512+
CheckTemplateParameterRAII CTP(*this, TP);
15121513
for (const auto &Capture : Intro.Captures) {
1513-
if (Capture.Id == TP->getIdentifier()) {
1514+
if (Capture.Id == TP->getIdentifier())
15141515
Diag(Capture.Loc, diag::err_template_param_shadow) << Capture.Id;
1515-
NoteTemplateParameterLocation(*TP);
1516-
}
15171516
}
15181517
}
15191518
}

‎clang/lib/Sema/SemaLookup.cpp

Lines changed: 10 additions & 4 deletions
Original file line numberDiff line numberDiff line change
@@ -1586,9 +1586,13 @@ llvm::DenseSet<Module*> &Sema::getLookupModules() {
15861586
unsigned N = CodeSynthesisContexts.size();
15871587
for (unsigned I = CodeSynthesisContextLookupModules.size();
15881588
I != N; ++I) {
1589-
Module *M = CodeSynthesisContexts[I].Entity ?
1590-
getDefiningModule(*this, CodeSynthesisContexts[I].Entity) :
1591-
nullptr;
1589+
auto &Ctx = CodeSynthesisContexts[I];
1590+
// FIXME: Are there any other context kinds that shouldn't be looked at
1591+
// here?
1592+
if (Ctx.Kind == CodeSynthesisContext::PartialOrderingTTP ||
1593+
Ctx.Kind == CodeSynthesisContext::CheckTemplateParameter)
1594+
continue;
1595+
Module *M = Ctx.Entity ? getDefiningModule(*this, Ctx.Entity) : nullptr;
15921596
if (M && !LookupModulesCache.insert(M).second)
15931597
M = nullptr;
15941598
CodeSynthesisContextLookupModules.push_back(M);
@@ -3709,7 +3713,8 @@ Sema::LookupLiteralOperator(Scope *S, LookupResult &R,
37093713
TemplateParameterList *Params = FD->getTemplateParameters();
37103714
if (Params->size() == 1) {
37113715
IsTemplate = true;
3712-
if (!Params->getParam(0)->isTemplateParameterPack() && !StringLit) {
3716+
NamedDecl *Param = Params->getParam(0);
3717+
if (!Param->isTemplateParameterPack() && !StringLit) {
37133718
// Implied but not stated: user-defined integer and floating literals
37143719
// only ever use numeric literal operator templates, not templates
37153720
// taking a parameter of class type.
@@ -3722,6 +3727,7 @@ Sema::LookupLiteralOperator(Scope *S, LookupResult &R,
37223727
if (StringLit) {
37233728
SFINAETrap Trap(*this);
37243729
CheckTemplateArgumentInfo CTAI;
3730+
CheckTemplateParameterRAII CTP(*this, Param);
37253731
TemplateArgumentLoc Arg(TemplateArgument(StringLit), StringLit);
37263732
if (CheckTemplateArgument(
37273733
Params->getParam(0), Arg, FD, R.getNameLoc(), R.getNameLoc(),

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