| Issue |
115418
|
| Summary |
[clang] [clangd] Missing information about explicit instantiation of function template
|
| Labels |
|
| Assignees |
|
| Reporter |
16bit-ykiko
|
```cpp
namespace test {
template <typename T>
void foo() {}
}
struct X {};
template void test::f^oo<X>();
```
Currently, if trigger go-to-definition at the location of `^`, clangd will give no response. And the tokens in the explicit instantiation are
also not highlighted. After some investigation, I found that the underlying cause is that the Clang frontend doesn't store the information about explicit instantiation of function templates.
Dump the AST of above code
```cpp
|-NamespaceDecl 0xd083678 <<source>:1:1, line:4:1> line:1:11 test
| `-FunctionTemplateDecl 0xd0838e8 <line:2:1, line:3:13> col:6 foo
| |-TemplateTypeParmDecl 0xd083708 <line:2:11, col:20> col:20 typename depth 0 index 0 T
| |-FunctionDecl 0xd083838 <line:3:1, col:13> col:6 foo 'void ()'
| | `-CompoundStmt 0xd0839c8 <col:12, col:13>
| `-FunctionDecl 0xd083d18 <col:1, col:13> col:6 foo 'void ()' explicit_instantiation_definition
| |-TemplateArgument type 'X'
| | `-RecordType 0xd083aa0 'X'
| | `-CXXRecord 0xd0839f8 'X'
| `-CompoundStmt 0xd0839c8 <col:12, col:13>
`-CXXRecordDecl 0xd0839f8 <line:6:1, col:11> col:8 referenced struct X definition
```
As you can see, the decl from explicit instantiation is only added to its semantic context but not to its lexical context.
If use a visitor to further explore:
```cpp
bool VisitFunctionTemplateDecl(clang::FunctionTemplateDecl* decl) {
for(auto spec: decl->specializations()) {
spec->getLocation().dump(srcMgr);
spec->getFunctionTypeLoc().getReturnLoc().getLocalSourceRange().dump(srcMgr)
spec->getQualifierLoc().getSourceRange().dump(srcMgr);
auto info = spec->getTemplateSpecializationInfo();
info->PointOfInstantiation.dump(srcMgr);
llvm::outs() << info->TemplateArguments << "\n";
llvm::outs() << info->TemplateArgumentsAsWritten << "\n";
}
return true;
}
```
The output is
```
test.cpp:3:6
<test.cpp:3:1>
<<invalid sloc>>
test.cpp:8:21
0x564cf04d7560
0x0
```
Only instantiation point is recorded correctly, all other information is from primary template. But for explicit specializations, the information is recorded properly.
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