terraform console: Multi-line entry support #34822
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The console command, when running in interactive mode, will now detect if the input seems to be an incomplete (but valid enough so far) expression, and if so will produce another prompt to accept another line of expression input. This is primarily to make it easier to paste in multi-line expressions taken from elsewhere, but it could also be used for manual input. The support for multi-line _editing_ is limited by the fact that the readline dependency we use doesn't support multiline input and so we're currently doing this in spite of that library. Hopefully we'll be able to improve on that in future either by contributing multi-line editing support upstream or by switching to a different readline dependency. The delimiter-counting heuristic employed here is similar to the one used by HCL itself to decide whether a newline should end the definition of an attribute, but this implementation is simpler because it doesn't need to produce error messages or perform any recovery. Instead, it just bails out if it encounters something strange so that the console session can return a parse error. Because some invalid input may cause a user to become "stuck" in a multi- line sequence, we consider a blank line as intent to immediately try to evaluate what was entered, and also interpret SIGINT (e.g. Ctrl+C) as cancellation of multi-line input, assuming that at least one line was already entered, extending the previous precedent that SIGINT cancels when at least one character was already entered at the prompt.
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jbardin
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Mar 13, 2024
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Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch. |
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I'm going to lock this pull request because it has been closed for 30 days ⏳. This helps our maintainers find and focus on the active contributions. |
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The console command, when running in interactive mode, will now detect if the input seems to be an incomplete (but valid enough so far) expression, and if so will produce another prompt to accept another line of expression input.
This is primarily to make it easier to paste in multi-line expressions taken from elsewhere, but it could also be used for manual input. The support for multi-line editing is limited by the fact that the readline dependency we use doesn't support multiline input and so we're currently doing this in spite of that library. Hopefully we'll be able to improve on that in future either by contributing multi-line editing support upstream or by switching to a different readline dependency.
The delimiter-counting heuristic employed here is similar to the one used by HCL itself to decide whether a newline should end the definition of an attribute, but this implementation is simpler because it doesn't need to produce error messages or perform any recovery. Instead, it just bails out if it encounters something strange so that the console session can return a parse error.
Because some invalid input may cause a user to become "stuck" in a multi- line sequence, we consider a blank line as intent to immediately try to evaluate what was entered, and also interpret SIGINT (e.g. Ctrl+C) as cancellation of multi-line input, extending the previous precedent that SIGINT cancels when at least one character was already entered at the prompt.
(This was just a little side-quest I did while waiting for some other work to be reviewed. I've been meaning to give this a try for a while, and was pleased to find that it was relatively easy to implement at least reasonable first pass of it.)