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Andy Jordan
7b6f602405
This adds the `EnableScreenReaderMode` command-line switch which defaults to true if an active screen reader is detected. In screen reader mode, the existing `ForceRender()` function is replaced by `RenderForScreenReader()` which uses a differential rendering approach to minimize extraneous output to the terminal, allowing the use of screen readers better than ever before. The differential rendering relies on calculating the common prefix of the `buffer` and `previousRender` strings. Nearly all necessary changes are consolidated in the new rendering function. Features known not to be supported: * Colors: as this necessitates redrawing to insert color sequences after the input is received and the AST parsed. * Inline predictions: as this by definition changes the suffix and thus requires endless redrawing. * List view predictions: since the render implementation never calls into the prediction engine, this is not available either. * Menu completion: well, it "works" since it's not disabled and does its own rendering, but no effort has been made to improve `DrawMenu()`, so it's not accessible (and I'm not sure it could be given our current constraints). Features known to be partially supported: * Text selection: mark and select commands work as intended, but provide no visual indication. * Multiple lines: as in newlines work fine, but there is no continuation prompt. * Visually wrapped lines: editing above a wrapped line redraws all subsequent lines and hence is noisy. * Status prompt based commands: what-is-key, digit-argument, and most notably, forward/backward incremental history search all render a "status prompt" on the line below the user's input buffer. This _is_ supported; however, it can be noisy since it necessarily has to render the whole buffer when the input buffer changes, including the status prompt (and search text). But what it's reading is almost always going to be relevant. Everything else should generally work, even Vi mode, and the tests pass. That said, this isn't perfect, and moreover the approach specifically doesn't attempt to enable things from the ground up. There may be features that are available but turn out not to be accessible (like `MenuComplete`) and I believe they should be left as-is. Specifically tested with NVDA on Windows and VoiceOver on macOS within VS Code's integrated terminal, with shell integration loaded, and Code's screen reader optimizations enabled.