verifyContext seems too strict when using adapted HashTable functions

[vkitchen]

Zig Version

0.12.0-dev.3639+9cfac4718

Steps to Reproduce and Observed Behavior

The following minimal reproduction compiles with an unexpected error. Where types are unequal due to constness however it is in the direction where a const function can't receive a non-const parameter

const std = @import("std");

pub fn main() !void {
    var arena = std.heap.ArenaAllocator.init(std.heap.page_allocator);
    const allocator = arena.allocator();

    const string_context: std.hash_map.StringContext = .{};
    var hash_map = std.StringHashMap([]u8).init(allocator);

    const key = try allocator.dupe(u8, "key");
    const gop = try hash_map.getOrPutAdapted(key, string_context);
    if (!gop.found_existing) {
        gop.key_ptr.* = key;
    }
}

Compiles with the following error

> zig build-exe test.zig
/usr/local/zig-linux-x86_64-0.12.0-dev.3639+9cfac4718/lib/std/hash_map.zig:340:13: error: Problems found with hash context type hash_map.StringContext:
                                                                                                hash_map.StringContext.hash must be fn (self, []u8) u64
                                                                                                  but is actually fn (hash_map.StringContext, []const u8) u64
                                                                                                  Second parameter must be []u8, but is []const u8
                                                                                                hash_map.StringContext.eql must be fn (self, []u8, []const u8) bool
                                                                                                  but is actually fn (hash_map.StringContext, []const u8, []const u8) bool
                                                                                                  Second parameter must be []u8, but is []const u8
            @compileError("Problems found with hash context type " ++ @typeName(Context) ++ ":" ++ errors);
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/zig-linux-x86_64-0.12.0-dev.3639+9cfac4718/lib/std/hash_map.zig:1174:35: note: called from here
            comptime verifyContext(@TypeOf(ctx), @TypeOf(key), K, Hash, false);
                     ~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/local/zig-linux-x86_64-0.12.0-dev.3639+9cfac4718/lib/std/hash_map.zig:1337:48: note: called from here
                    const index = self.getIndex(key, key_ctx) orelse return err;

Expected Behavior

The program to compile as casting to const is safe