Backport "Fix "Fix Ctrl-C Handling in the REPL"" to 3.8.4#25874
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WojciechMazur merged 1 commit intorelease-3.8.4from Apr 20, 2026
Merged
Backport "Fix "Fix Ctrl-C Handling in the REPL"" to 3.8.4#25874WojciechMazur merged 1 commit intorelease-3.8.4from
WojciechMazur merged 1 commit intorelease-3.8.4from
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Follow-up from #25782. This PR lets us get the best of both worlds: `Ctrl-C` handling works even in the subprocess scenario, and `System.in.read()` works too. Basically rather than having two threads reading from `System.in` at the same time, we wrap `System.in` in our own wrapper such that we can peek at it without dropping the characters we read on the floor. This lets us check for Ctrl-C from the REPL infrastructure while still ensuring that all System.in characters end up being correctly sent to any `System.in.read()` calls made by user code in the REPL I haven't looked at the JShell sources since that is prohibited, but it seems they do a similar sort of wrapping, as empirically JShell is able to handle `System.in.read` while still capturing Ctrl-C and handling that appropriately as well, and `System.in` in JShell is a wrapper input rather than a raw `java.io.BufferedInputStream` ```scala jshell> System.in $1 ==> jdk.jshell.execution.Util$1@31a5c39e ``` ## How much have you relied on LLM-based tools in this contribution? Extensively ## How was the solution tested? Tested manually via `./mill repl`. 1. Verified that without this PR `Ctrl-C` handling does not work due to the REPL running in a subprocess, with this PR Ctrl-C is properly caught. 2. Also verified that without this PR, `System.in.read()` in the REPL returns `-1`, whereas with this PR `System.in.read()` in the REPL correctly prompts the user to enter input, and prints the ascii code of the character entered Also verified the original `def askQuestion` scenario which now seems to work [Cherry-picked 7fd3dcd]
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Backports #25835 to the 3.8.4-RC2.
PR submitted by the release tooling.