Further AST integration and API refinement before introducing the new synchronization mechanism.
closes#8609
# Important Notes
API changes:
- Renamed `Ast.parseExpression` / `Ast.parse` to better reflect their usage:
- `Ast.parse` returns a block or a single expression, depending on its input; this is convenient for expressions expected to be single-line.
- `Ast.parseBlock` always treats its input as a block; this is suitable for parsing a file.
- `astExtended` is no longer needed to access span information. `Ast.span` provides access to the value when appropriate (the project's committed modules have spans; uncommitted changes or other parsed expressions don't).
- `SourceRange` is now used everywhere in place of `ContentRange`--the two types had the same definition.
Features:
- Fix CodeEditor viewing.
Implementation improvements:
- Updated widget update handlers (#8545) implementation to Ast API.
- Integrated `imports` more thoroughly with new AST APIs.
- More tests.
- The module is edited by changing the AST, not the text representation.
- `IdMap`s no longer need to be maintained in parallel with the module content; they are snapshots produced as needed from the ASTs.
- Simplistic synchronization is in place until #8237: Edits are never merged; if two edits are started from the same state, one will be overwritten.
- Depends on #7773.
- Implements binary WebSocket protocol (data protocol)
- Performs some editor initialization (the bare minimum so that visualizations work)
- Adds event handlers to receive visualization data updates
# Important Notes
None
