[cfe-dev] [AST Visitor] Default parameters of template functions

[Andrzej Kotulski via cfe-dev]

I’m looking to get value of default parameter for templated functions/methods – clang for some reason doesn’t export this information in expected way (VarDecl::getInitExpr() in specialization declaration)
For example, look at AST for following code (-ast-dump below):

template<class T> void default_int(int a = 0) {}
template<class T> void default_T(T a = T(0)) {}
void test() {
  default_int<int>();
  default_T<int>();
}

None of the template specializations have any information about default argument.
1. For default_int<int> it’s not a big deal – we can read that information from FunctionTemplateDecl and apply it to all specializations
2. For default_T<int> problem is harder – parameter in FunctionTemplateDecl will have CXXUnresolvedConstructExpr as init expression which is not so useful. I imagine clang already resolves that ConstructExpr, but it’s not put to ParmVarDecl.

Question:
Is there general way of accessing default parameter value for both cases (1) and (2)? Is there any reason why it’s not initExpr of ParmVarDecl?


clang -c default.cpp -Xclang -ast-dump
TranslationUnitDecl 0x103030cc0 <<invalid sloc>> <invalid sloc>
|-TypedefDecl 0x103031200 <<invalid sloc>> <invalid sloc> implicit __int128_t '__int128'
|-TypedefDecl 0x103031260 <<invalid sloc>> <invalid sloc> implicit __uint128_t 'unsigned __int128'
|-TypedefDecl 0x103031660 <<invalid sloc>> <invalid sloc> implicit __builtin_va_list '__va_list_tag [1]'
|-FunctionTemplateDecl 0x103031900 <default.cpp:1:1, col:48> col:24 default_int
| |-TemplateTypeParmDecl 0x1030316b0 <col:10, col:16> col:16 class T
| |-FunctionDecl 0x103031850 <col:19, col:48> col:24 default_int 'void (int)'
| | |-ParmVarDecl 0x103031770 <col:36, col:44> col:40 a 'int' cinit
| | | `-IntegerLiteral 0x1030317d0 <col:44> 'int' 0
| | `-CompoundStmt 0x103031958 <col:47, col:48>
| `-FunctionDecl 0x103072c00 <col:19, col:48> col:24 used default_int 'void (int)'
|   |-TemplateArgument type 'int'
|   |-ParmVarDecl 0x103072b70 <col:36, col:44> col:40 a 'int'
|   `-CompoundStmt 0x103031958 <col:47, col:48>
|-FunctionTemplateDecl 0x103072810 <line:2:1, col:47> col:24 default_T
| |-TemplateTypeParmDecl 0x103031970 <col:10, col:16> col:16 referenced class T
| |-FunctionDecl 0x103072760 <col:19, col:47> col:24 default_T 'void (T)'
| | |-ParmVarDecl 0x103072600 <col:34, col:43> col:36 a 'T' cinit
| | | `-CXXUnresolvedConstructExpr 0x103072690 <col:40, col:43> 'T'
| | |   `-IntegerLiteral 0x103072670 <col:42> 'int' 0
| | `-CompoundStmt 0x103072868 <col:46, col:47>
| `-FunctionDecl 0x103073140 <col:19, col:47> col:24 used default_T 'void (int)'
|   |-TemplateArgument type 'int'
|   |-ParmVarDecl 0x103073080 <col:34, col:43> col:36 a 'int':'int'
|   `-CompoundStmt 0x103072868 <col:46, col:47>
`-FunctionDecl 0x1030728d0 <line:3:1, line:6:1> line:3:6 test 'void (void)'
  `-CompoundStmt 0x1030733a8 <col:13, line:6:1>
    |-CallExpr 0x103072dd0 <line:4:3, col:20> 'void'
    | |-ImplicitCastExpr 0x103072db8 <col:3, col:18> 'void (*)(int)' <FunctionToPointerDecay>
    | | `-DeclRefExpr 0x103072d10 <col:3, col:18> 'void (int)' lvalue Function 0x103072c00 'default_int' 'void (int)' (FunctionTemplate 0x103031900 'default_int')
    | `-CXXDefaultArgExpr 0x103072e08 <<invalid sloc>> 'int'
    `-CallExpr 0x103073310 <line:5:3, col:18> 'void'
      |-ImplicitCastExpr 0x1030732f8 <col:3, col:16> 'void (*)(int)' <FunctionToPointerDecay>
      | `-DeclRefExpr 0x103073250 <col:3, col:16> 'void (int)' lvalue Function 0x103073140 'default_T' 'void (int)' (FunctionTemplate 0x103072810 'default_T')
      `-CXXDefaultArgExpr 0x103073380 <<invalid sloc>> 'int':'int'
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