How does the compiler know two generic types are the same?

[Sze]

I think this post and topic is required reading to get a deeper grasp of how comptime works:

How Zig incremental compilation is implemented internally?

What’s an “IES”? Oops, sorry! IES stands for “inferred error set”. When a function has an inferred error set (fn foo() !void { ... }), then code which e.g. performs a switch on that error set has to “resolve” it: figure out the concrete errors it contains. To do that, we have to analyze the function body if we haven’t already so that we encounter all ZIR that could return errors, which implicitly adds them to the IES. How “values” work? […] Yep, your understanding is totally right, and …