| 1 | // Copyright (c) Meta Platforms, Inc. and affiliates. |
| 2 | // |
| 3 | // This source code is licensed under the MIT license found in the |
| 4 | // LICENSE file in the root directory of this source tree. |
| 5 | |
| 6 | //! Flattens labeled terminals where the label is not reachable, and |
| 7 | //! nulls out labels for other terminals where the label is unused. |
| 8 | //! |
| 9 | //! Corresponds to `src/ReactiveScopes/PruneUnusedLabels.ts`. |
| 10 | |
| 11 | use rustc_hash::FxHashSet; |
| 12 | |
| 13 | use react_compiler_hir::{ |
| 14 | BlockId, ReactiveFunction, ReactiveStatement, ReactiveTerminal, ReactiveTerminalStatement, |
| 15 | ReactiveTerminalTargetKind, environment::Environment, |
| 16 | }; |
| 17 | |
| 18 | use crate::visitors::{ReactiveFunctionTransform, Transformed, transform_reactive_function}; |
| 19 | |
| 20 | /// Prune unused labels from a reactive function. |
| 21 | pub fn prune_unused_labels( |
| 22 | func: &mut ReactiveFunction, |
| 23 | env: &Environment, |
| 24 | ) -> Result<(), react_compiler_diagnostics::CompilerError> { |
| 25 | let mut transform = Transform { env }; |
| 26 | let mut labels: FxHashSet<BlockId> = FxHashSet::default(); |
| 27 | transform_reactive_function(func, &mut transform, &mut labels) |
| 28 | } |
| 29 | |
| 30 | struct Transform<'a> { |
| 31 | env: &'a Environment, |
| 32 | } |
| 33 | |
| 34 | impl<'a> ReactiveFunctionTransform for Transform<'a> { |
| 35 | type State = FxHashSet<BlockId>; |
| 36 | |
| 37 | fn env(&self) -> &Environment { |
| 38 | self.env |
| 39 | } |
| 40 | |
| 41 | fn transform_terminal( |
| 42 | &mut self, |
| 43 | stmt: &mut ReactiveTerminalStatement, |
| 44 | state: &mut FxHashSet<BlockId>, |
| 45 | ) -> Result<Transformed<ReactiveStatement>, react_compiler_diagnostics::CompilerError> { |
| 46 | // Traverse children first |
| 47 | self.traverse_terminal(stmt, state)?; |
| 48 | |
| 49 | // Collect labeled break/continue targets |
| 50 | match &stmt.terminal { |
| 51 | ReactiveTerminal::Break { |
| 52 | target, |
| 53 | target_kind: ReactiveTerminalTargetKind::Labeled, |
| 54 | .. |
| 55 | } |
| 56 | | ReactiveTerminal::Continue { |
| 57 | target, |
| 58 | target_kind: ReactiveTerminalTargetKind::Labeled, |
| 59 | .. |
| 60 | } => { |
| 61 | state.insert(*target); |
| 62 | } |
| 63 | _ => {} |
| 64 | } |
| 65 | |
| 66 | // Is this terminal reachable via a break/continue to its label? |
| 67 | let is_reachable_label = stmt |
| 68 | .label |
| 69 | .as_ref() |
| 70 | .map_or(false, |label| state.contains(&label.id)); |
| 71 | |
| 72 | if let ReactiveTerminal::Label { block, .. } = &mut stmt.terminal { |
| 73 | if !is_reachable_label { |
| 74 | // Flatten labeled terminals where the label isn't necessary. |
| 75 | // Note: In TS, there's a check for `last.terminal.target === null` |
| 76 | // to pop a trailing break, but since target is always a BlockId (number), |
| 77 | // that check is always false, so the trailing break is never removed. |
| 78 | let flattened = std::mem::take(block); |
| 79 | return Ok(Transformed::ReplaceMany(flattened)); |
| 80 | } |
| 81 | } |
| 82 | |
| 83 | if !is_reachable_label { |
| 84 | if let Some(label) = &mut stmt.label { |
| 85 | label.implicit = true; |
| 86 | } |
| 87 | } |
| 88 | |
| 89 | Ok(Transformed::Keep) |
| 90 | } |
| 91 | } |