I'm currently implementing a clang tool. I have no idea how to find out the noexcept-ness of a function given its clang::FunctionDecl. For the following code

我目前正在实现一个Clang工具。在给定clang：：FunctionDecl的情况下，我不知道如何找出函数的非异常。对于以下代码，

struct X {
  X() = default;
};

int main() {
  X x;
}

clang-query shows that the default constructor of X is noexcept:

Clang-Query显示X的默认构造函数为NOEXCEPT：

-CXXConstructorDecl 0x563b8aea50e8 <line:2:3, col:15> col:3 used constexpr X 'void () noexcept' default trivial implicit-inline
 `-CompoundStmt 0x563b8aea5768 <col:15>

but fd->getExceptionSpecType() returns clang::ExceptionSpecificationType::EST_None. Moreover, I think the noexcept-ness might also be encoded in the function type (since it is part of the function type since C++17), but I don't know how to extract that information.

但是fd->getExceptionspecType()返回clang：：ExceptionSpecificationType：：est_None。此外，我认为异常也可能编码在函数类型中(因为它是从C++17开始的函数类型的一部分)，但我不知道如何提取该信息。

To get the ExceptionSpecificationType of a
FunctionDecl,
call
ValueDecl::getType()
to get its
QualType,
call getTypePtr() on that to get its
Type,
then use
dyn_cast
to downcast that to a
FunctionProtoType,
and finally call
FunctionProtoType::getExceptionSpecType().

要获取FunctionDecl的ExceptionSpecificationType，请调用ValueDecl：：getType()以获取其QualType，对其调用getTypePtr()以获取其Type，然后使用dyn_cast将其向下转换为FunctionProtoType，最后调用FunctionProtoType：：getExceptionspecType()。

For example:

例如：

clang::FunctionDecl const *functionDecl = /*wherever*/;
clang::Type const *type = functionDecl->getType().getTypePtr();
if (auto fpt = dyn_cast<clang::FunctionProtoType>(type)) {
  clang::ExceptionSpecificationType est = fpt->getExceptionSpecType();
  // Now do something with 'est'.
}

On your example, for X::X(), the above yields EST_BasicNoexcept.

在您的示例中，对于X：：X()，上面的代码会生成EST_BasicNoExcept。

(I'm using Clang+LLVM-16.0.0 on Linux, but this should be the same
across a fairly wide range of versions.)

(我在Linux上使用的是Clang+LLVM-16.0.0，但在相当广泛的版本中应该是相同的。)

Why doesn't FunctionDecl::getExceptionSpecType work?

The documentation for FunctionDecl::getExceptionSpecType() says:

FunctionDecl：：getExceptionspecType()的文档中写道：

Gets the ExceptionSpecificationType as declared.

The "as declared" part means it only includes noexcept if that was
syntactically present.

“如声明的”部分意味着它只包括no，除非它在句法上存在。

In contrast, by going through the FunctionProtoType, we get implicit
exception specifications too.

相反，通过FunctionProtoType，我们也得到了隐式异常规范。

Caveat: Unevaluated exception specifications

If you remove the main function from the example, then the above
snippet instead yields EST_Unevaluated, whose documentation says:

如果从示例中删除Main函数，则上面的代码段将生成EST_UNEVALUATED，其文档如下所示：

not evaluated yet, for special member function

Digging through the sources (e.g.,
SemaExceptionSpec.cpp:1056,
etc.), it seems that implicit exception specifications for constructors
and the like are not computed until needed. A call site is a "need", as
is a virtual override, perhaps among a few other cases.

深入研究源代码(例如，SemaExceptionspec.cpp：1056等)，似乎直到需要时才计算构造函数等的隐式异常规范。调用点是一种“需要”，就像虚拟覆盖一样，或许还有其他几种情况。

Supplementary

If you want to go deeper on exception specifications, you may want to
look at
ExceptionAnalyzer.cpp
in the Clang sources, since that does a bunch of analysis of exception
specification semantics.

如果您想更深入地了解异常规范，您可能需要查看Clang源代码中的ExceptionAnalyzer.cpp，因为它会对异常规范语义进行大量分析。