Input range + filter + chain => First element vanishes

[dlangBugzillaToGithub]

qigezx+dc40d6nao940k reported this on 2024-09-20T12:56:08Z

Transfered from https://issues.dlang.org/show_bug.cgi?id=24774

Description

Chaining another range after a filtered input range omits the first element.

Minimal example:

import std.stdio;
import std.algorithm;
import std.range;

void main(){
	int i = 0;
	int gen(){
		return i++;
	}

	auto r1 = generate!gen.until!(x=> x>10);
	auto r2 = only(100);

	// Will print [7.8,9,10,100]
	// 6 is missing
	r1.filter!"a>5".chain(r2).writeln;

	// By adding "array" before chain, it will behave properly
	// [6,7,8,9,10,100]
	// r1.array.filter!"a>5".chain(r2).writeln;
	// r1.filter!"a>5".array.chain(r2).writeln;
}

>dmd --version
DMD64 D Compiler v2.109.1

Copyright (C) 1999-2024 by The D Language Foundation, All Rights Reserved written by Walter Bright

os: linux x64