[all-commits] [llvm/llvm-project] 4b8b70: [Clang] Fix dependence handling of nttp for variab...

[刘雨培 via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 4b8b70a52fa4d133a19f620c8a9160793ded08b5
      https://github.com/llvm/llvm-project/commit/4b8b70a52fa4d133a19f620c8a9160793ded08b5
  Author: 刘雨培 <liuyupei951018 at hotmail.com>
  Date:   2023-10-16 (Mon, 16 Oct 2023)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/AST/ExprCXX.h
    M clang/lib/AST/ASTImporter.cpp
    M clang/lib/AST/ExprCXX.cpp
    M clang/lib/Sema/SemaDeclCXX.cpp
    M clang/lib/Sema/SemaTemplate.cpp
    M clang/test/SemaTemplate/dependent-expr.cpp

  Log Message:
  -----------
  [Clang] Fix dependence handling of nttp for variable templates (#69075)

The dependence of a template argument is not only determined by the
argument itself, but also by the type of the template parameter:

> Furthermore, a non-type
[template-argument](https://eel.is/c++draft/temp.names#nt:template-argument)
is dependent if the corresponding non-type
[template-parameter](https://eel.is/c++draft/temp.param#nt:template-parameter)
is of reference or pointer type and the
[template-argument](https://eel.is/c++draft/temp.names#nt:template-argument)
designates or points to a member of the current instantiation or a
member of a dependent
type[.](https://eel.is/c++draft/temp.dep#temp-3.sentence-1)

For example:

```cpp
struct A{};

template <const A& T>
const A JoinStringViews = T;

template <int V>
class Builder {
public:
    static constexpr A Equal{};
    static constexpr auto Val = JoinStringViews<Equal>;
};
```

The constant expression `Equal` is not dependent, but because the type
of the template parameter is a reference type and `Equal` is a member of
the current instantiation, the template argument of
`JoinStringViews<Equal>` is actually dependent, which makes
`JoinStringViews<Equal>` dependent.

When a template-id of a variable template is dependent,
`CheckVarTemplateId` will return an `UnresolvedLookupExpr`, but
`UnresolvedLookupExpr` calculates dependence by template arguments only
(the `ConstantExpr` `Equal` here), which is not dependent. This causes
type deduction to think that `JoinStringViews<Equal>` is `OverloadTy`
and treat it as a function template, which is clearly wrong.

This PR adds a `KnownDependent` parameter to the constructor of
`UnresolvedLookupExpr`. After canonicalization, if `CanonicalConverted`
contains any dependent argument, `KnownDependent` is set to `true`. This
fixes the dependence calculation of `UnresolvedLookupExpr` for dependent
variable templates.

Fixes #65153 .