[cfe-dev] RFC: Easier AST Matching by Default

[Stephan Bergmann via cfe-dev]

On 27/05/2020 11:34, Stephen Kelly via cfe-dev wrote:
> On Wed 27 May 2020, 09:25 Sam McCall, <sammccall at google.com 
> <mailto:sammccall at google.com>> wrote:
>     In summary: it requires changes in consuming tools that are
>     numerous, hard to find, hard to analyze, must all be done at once,
>     and the changes aren't mechanically reliable.
> 
> 
> Hmm, the location to call setTraversalKind on the ParentMapContext in 
> each external tool should be easy to find? Should be easy to analyze 
> too. There is presumably fewer places in your tool (or just one place in 
> the entire tool)  where ASTContexts are created, so "all" is either "1" 
> or close to it?
> 
>     I expect this to bite people building tools against release versions
>     to hit the same problems in a few months.
> 
> 
> Perhaps the solution of changing the setting in the ParentMapContext 
> needs to be spelled out better in the release notes. It would also be 
> good to know whether doing so makes the impact on your tools manageable. 
> Can you look into that?

As a side note:  When adapting LibreOffice's Clang plugin to this 
change, it wasn't clear to me whether that plugin would be allowed to 
call setTraversalKind (to set it back to the old TK_AsIs) on the global 
CompilerInstance's ASTContext's ParentMapContext, so I ended up using a 
private ParentMapContext for the plugin 
(<https://git.libreoffice.org/core/+/09aa5a9be8b9b3c88cf25b85e0eda28c5ef19aa4%5E!/> 
"Adapt to changed clang::ASTContext::getParents behavior on Clang 11 
trunk").