Tracking Issue for `hash_map!` macro

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Feature gate: #![feature(hash_map_macro)]

This is a tracking issue for https://github.com/rust-lang/libs-team/issues/578

The hash_map! macro is like the vec! macro but for HashMaps, it aims to help create hash_maps with set keys for functions that require dynamic key value pairs such as a templating engine asking to fill the templates with a HashMap.

Public API

use std::hash_map;

fn main() {
    let map = hash_map! {
        "key" => "value",
        "key2" => "value2"
    }; // uses type inference.

    for (key, value) in map {
        println!("{key:?} => {value:?}");
    }
}

Steps / History

(Remember to update the S-tracking-* label when checking boxes.)

• Implementation: #144070
• Reverted in #148049 due to #147971
• Re-implemented in #154322
• Final comment period (FCP)^1
• Stabilization PR

Unresolved Questions

• What separator should we use? the main proposition was =>, : was also proposed.
• Should this macro allow using other hashers in it's syntax? If so, how?

Begin by reading the linked libs-team issue #578 and the implementation history in PRs #144070, #148049, and #154322. Review the unresolved separator and hasher questions, then check the feature lifecycle requirements; done means the final comment period and stabilization PR are complete.