rea/src/domain/javascript/javascriptSemanticReferenceSources.ts

import type * as t from "@babel/types";
import type { JavaScriptSemanticAnalysisState } from "./javascriptSemanticState.js";
import type { JavaScriptSemanticPropertyPath as PropertyPath } from "./javascriptSemanticPropertyPaths.js";
import { evaluateSemanticExpression } from "./javascriptSemanticValues.js";
import { semanticSlotAtPath } from "./javascriptSemanticSlots.js";

interface ReferenceSource {
  readonly node: t.Node;
  readonly projection: PropertyPath;
}

/** Exclude references whose source slot or destructuring fallback is absent. */
export const semanticReferenceSourcesInactive = (
  reference: {
    readonly requiredSources?: readonly ReferenceSource[];
    readonly fallbackSources?: readonly ReferenceSource[];
  },
  state: JavaScriptSemanticAnalysisState,
): boolean =>
  reference.requiredSources?.some(
    (source) =>
      semanticSelectedReferenceSlot(source, state, source.node)?.presence ===
      "absent",
  ) === true ||
  reference.fallbackSources?.some((source) => {
    // Selection precedes effects through the chosen reference. A later escape
    // cannot make a fallback that was excluded at destructuring reachable.
    const slot = semanticSelectedReferenceSlot(source, state, source.node);
    return (
      slot?.presence === "present" &&
      (slot.value.status === "literal" ||
        slot.value.status === "union" ||
        slot.value.status === "object" ||
        slot.value.status === "array")
    );
  }) === true;

/** Select a retained source slot at its capture, before later effects. */
export const semanticSelectedReferenceSlot = (
  source: ReferenceSource,
  state: JavaScriptSemanticAnalysisState,
  capturePoint?: t.Node,
) => {
  const path: string[] = [];
  for (const key of source.projection) {
    if (key === null || typeof key === "object") return undefined;
    path.push(String(key));
  }
  return semanticSlotAtPath(
    evaluateSemanticExpression(source.node, state, capturePoint),
    path,
  );
};