[REQUEST]: Identify duplicate demangled symbols about compiler-explorer HOT 3 CLOSED

rustc has two name mangling schemes, legacy (the default for now) and v0 (which will become the default at some point in the future).

legacy disambiguates duplicate symbol names (such as the call_once methods of different closures) by including a unique-per-symbol hash in each name. CE’s demangler could include this hash, but doesn’t currently. FWIW, c++filt includes the hash by default.

v0 was designed so that a demangled name should be unique by itself. (Note: It still uses a hash to disambiguate crates with the same name.)

Always including the hash might make sense for legacy mangling, but for v0 it’s mostly unnecessary information (duplicate crates in different versions are rare on CE, also the v0 RFC recommends omitting the crate-id), so I’d suggest a new checkbox Options... → Include disambiguating hashes in identifiers (wording TBD) that controls whether hashes are included. Another wording could be Verbose demangling, which is what c++filt calls this.

v0 demanglings for a closure’s call_once method without and with crate-ids:

<example::get_multiplier::{closure#0} as core::ops::function::FnOnce<(u32, u32)>>::call_once:
<example[e8d519bf5b4bcf09]::get_multiplier::{closure#0} as core[5a612027cd243909]::ops::function::FnOnce<(u32, u32)>>::call_once:

As a workaround, -C symbol-mangling-version=v0 can be passed to the compiler: https://godbolt.org/z/zxEf7P6rj

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Using v0 if available seems to make a lot more sense to me.
It's not easy to add something like a counter as it will require a lot more logic, or we would have to make them unique by adding the hash to the demangled name.

(for reference, demangler is here https://github.com/compiler-explorer/tools/blob/main/rust/src/main.rs (we might need to rebuild this anyway) - but the names are passed 1 by 1 by this TS code https://github.com/compiler-explorer/compiler-explorer/tree/main/lib/demangler)

(we use this for c++ (demanglerType=cpp) -> https://github.com/compiler-explorer/compiler-explorer/blob/main/lib/demangler/cpp.ts to add extra text to the demangled names)

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I implemented the checkbox I proposed in #6265.

Also, this issue has come up before: #1754.

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