[Lldb-commits] [lldb] [lldb] Implement priority system for symbol locator plugin (PR #144406)

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GeorgeHuyubo wrote:

> I don't yet understand how changing the priority of the plugins prevents the "double download" you mention. Your problem statements talks about the callback and the debuginfod plugin, but your solution talks about the debuginfod plugin and the default symbol locator. What confuses me is that `locate_module` mechanism isn't using the symbol locator plugin mechanism. How does prioritizing one plugin over another prevent us from invoking the callback? Is this somehow called from the default symbol locator (I tried to look at the code but couldn't immediately find something like that).

So I believe the locate_module callback is designed for user to do something like:
```
symbol_file_spec.SetDirectory(symbol_dir)
symbol_file_spec.SetFilename(symbol_name + suffix)
```
...after the callback function finish downloading the symbol. This means that we still rely on the Default symbol locator(which should simply look for symbol locally by the dir&filename) to actually locate the symbol file. But if debuginfod is also enabled and called first, debuginfod plugin will ignore the local symbol file(even if it exist), but query the debuginfod server by the gnu_build_id, and do a double downloading.

https://github.com/llvm/llvm-project/pull/144406