static analysis

pr_agent/static_analysis/tests/example_files/match.ts

@@ -0,0 +1,138 @@
+// @ts-ignore
+import { Pattern } from './types/Pattern'; // @ts-ignore
+import { Match } from './types/Match'; // @ts-ignore
+import * as symbols from './internals/symbols'; // @ts-ignore
+import { matchPattern } from './internals/helpers'; // @ts-ignore
+
+type MatchState<output> =
+  | { matched: true; value: output }
+  | { matched: false; value: undefined };
+
+const unmatched: MatchState<never> = {
+  matched: false,
+  value: undefined,
+};
+
+/**
+ * `match` creates a **pattern matching expression**.
+ *  * Use `.with(pattern, handler)` to pattern match on the input.
+ *  * Use `.exhaustive()` or `.otherwise(() => defaultValue)` to end the expression and get the result.
+ *
+ * [Read the documentation for `match` on GitHub](https://github.com/gvergnaud/ts-pattern#match)
+ *
+ * @example
+ *  declare let input: "A" | "B";
+ *
+ *  return match(input)
+ *    .with("A", () => "It's an A!")
+ *    .with("B", () => "It's a B!")
+ *    .exhaustive();
+ *
+ */
+export function match<const input, output = symbols.unset>(
+  value: input
+): Match<input, output> {
+  return new MatchExpression(value, unmatched) as any;
+}
+
+/**
+ * This class represents a match expression. It follows the
+ * builder pattern, we chain methods to add features to the expression
+ * until we call `.exhaustive`, `.otherwise` or the unsafe `.run`
+ * method to execute it.
+ *
+ * The types of this class aren't public, the public type definition
+ * can be found in src/types/Match.ts.
+ */
+class MatchExpression<input, output> {
+  constructor(private input: input, private state: MatchState<output>) {}
+
+  with(...args: any[]): MatchExpression<input, output> {
+    if (this.state.matched) return this;
+
+    const handler: (selection: unknown, value: input) => output =
+      args[args.length - 1];
+
+    const patterns: Pattern<input>[] = [args[0]];
+    let predicate: ((value: input) => unknown) | undefined = undefined;
+
+    if (args.length === 3 && typeof args[1] === 'function') {
+      // case with guard as second argument
+      patterns.push(args[0]);
+      predicate = args[1];
+    } else if (args.length > 2) {
+      // case with several patterns
+      patterns.push(...args.slice(1, args.length - 1));
+    }
+
+    let hasSelections = false;
+    let selected: Record<string, unknown> = {};
+    const select = (key: string, value: unknown) => {
+      hasSelections = true;
+      selected[key] = value;
+    };
+
+    const matched =
+      patterns.some((pattern) => matchPattern(pattern, this.input, select)) &&
+      (predicate ? Boolean(predicate(this.input)) : true);
+
+    const selections = hasSelections
+      ? symbols.anonymousSelectKey in selected
+        ? selected[symbols.anonymousSelectKey]
+        : selected
+      : this.input;
+
+    const state = matched
+      ? {
+          matched: true as const,
+          value: handler(selections, this.input),
+        }
+      : unmatched;
+
+    return new MatchExpression(this.input, state);
+  }
+
+  when(
+    predicate: (value: input) => unknown,
+    handler: (selection: input, value: input) => output
+  ): MatchExpression<input, output> {
+    if (this.state.matched) return this;
+
+    const matched = Boolean(predicate(this.input));
+
+    return new MatchExpression<input, output>(
+      this.input,
+      matched
+        ? { matched: true, value: handler(this.input, this.input) }
+        : unmatched
+    );
+  }
+
+  otherwise(handler: (value: input) => output): output {
+    if (this.state.matched) return this.state.value;
+    return handler(this.input);
+  }
+
+  exhaustive(): output {
+    return this.run();
+  }
+
+  run(): output {
+    if (this.state.matched) return this.state.value;
+
+    let displayedValue;
+    try {
+      displayedValue = JSON.stringify(this.input);
+    } catch (e) {
+      displayedValue = this.input;
+    }
+
+    throw new Error(
+      `Pattern matching error: no pattern matches value ${displayedValue}`
+    );
+  }
+
+  returnType() {
+    return this;
+  }
+}