Warn about dead code within `match` and `if`/`else`

[jorgeluismireles]

Describe the feature

A programmer mistake can produce dead code if uses within if/else branches comparisons like a == a and within match like match a { a { ... } else { ... } }.

The compiler could look for these types of comparisons and issue warnings about the possibility of dead code.

Use Case

Dead code with if and else:

fn f1(a int) string {
	if a == a {
		return 'a' // always
	} else if a == a {
		return 'a again' // never happens
	} else {
		return 'other' // never happens
	}
}

Dead code within match:

fn f2(a int) string {
	return match a {
		a { 'a' } // always
		1 { '1' } // never
		else { 'else' } // never
	}
}

match is more robust than if/else since already prevents repeated constants and exhaust the search with mandatory else. But with variables or post-calculated constants also can produce dead code. Some examples are in issue #23403

Proposed Solution

No response

Other Information

No response

Acknowledgements

• I may be able to implement this feature request
• This feature might incur a breaking change

Version used

V 0.4.9 9fc8352

Environment details (OS name and version, etc.)

Playground

_{Huly®: V_0.6-21835}

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