fix: give compile error for infinite range in format

[DeterminedSage]

Remaining Fix: #10559

Summary

This PR tackles the issue of infinite loop during runtime when providing format with infinte range . Now it shows compilation error for the same .

Root Cause

Passing an infinite range (e.g., 42.repeat) to format("%s", ...) would result in the format engine trying to consume the entire range, which leads to a non-terminating loop at runtime .

format did not have a guard to catch infinite ranges. This allowed constructs like :

auto s = format("%s", 42.repeat); // hangs forever

to compile successfully but hang during execution.

Fix

This patch adds a static assert within the formatRange function that triggers at compile time if the range is detected to be infinite and the formatting is not in test mode (Writer != NoOpSink).

    static if (!formatTestMode && isInfinite!T)
    {
        static assert(!isInfinite!T, "Cannot format an infinite range. " ~
            "Convert it to a finite range first using `std.range.take` or `std.range.takeExactly`.");
    }

This ensures that formatting infinite ranges directly is disallowed unless the user explicitly converts them to finite ranges using 'std.range.take' or 'std.range.takeExactly' .

Example Reproducer

import std.format, std.range;

void main() {
    auto r = 1.repeat;
    auto s = format("%s", r); // used to hang at runtime
}

Now results in a compile-time error:

Error: static assert:  "Cannot format an infinite range. Convert it to a finite range first using `std.range.take` or `std.range.takeExactly`."

Notes

A corresponding unittest has been updated to explicitly verify this behavior using static assert(!__traits(compiles, ...)), confirming that formatting infinite ranges is correctly disallowed at compile time.

Verified manually using a custom Phobos build and test suite.

Completes the second half of issue #10559, which was partially fixed in PR #10744 .

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Bugzilla references

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If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + phobos#10752"

[rikkimax]

If no one has any opinions on this, I've set it to merge in 72 hours.
Feel free to remove tag/merge if desired.

[jmdavis]

It would appear that there's something wrong with the 72h merge label.

[DeterminedSage]

It would appear that there's something wrong with the 72h merge label.

Seems to be the case , was about to ping you

[0xEAB]

Like Nic once told me:

[…] the bot has always been a bit flakey

[schveiguy]

AFAIK, the 72h merge is a label only, the bot doesn't look at it.