async discoverVariants()

in scripts/compilation/Inliner.js [67:147]
58 lines of code
14 McCabe index (conditional complexity)

  async discoverVariants() {
    if (this.bailout) {
      console.log("Inliner bailout.");
      return this;
    }
    this.variantEntries = Object.entries(this.pkgJson["react-native"] ?? {});

    for await (const file of walk(path.join(this.packageDirectory, "dist-cjs"))) {
      if (file.endsWith(".js") && fs.existsSync(file.replace(/\.js$/, ".native.js"))) {
        console.log("detected undeclared auto-variant", file);
        const canonical = file.replace(/(.*?)dist-cjs\//, "./dist-cjs/").replace(/\.js$/, "");
        const variant = canonical.replace(/(.*?)(\.js)?$/, "$1.native$2");

        this.variantEntries.push([canonical, variant]);
      }
      if (fs.existsSync(file.replace(/\.js$/, ".browser.js"))) {
        // not applicable to CJS?
      }
    }

    this.transitiveVariants = [];

    for (const [k, v] of this.variantEntries) {
      for (const variantFile of [k, String(v)]) {
        if (!variantFile.includes("dist-cjs/")) {
          continue;
        }
        const keyFile = path.join(
          this.packageDirectory,
          "dist-cjs",
          variantFile.replace(/(.*?)dist-cjs\//, "") + (variantFile.endsWith(".js") ? "" : ".js")
        );
        const keyFileContents = fs.readFileSync(keyFile, "utf-8");
        const requireStatements = keyFileContents.matchAll(/require\("(.*?)"\)/g);
        for (const requireStatement of requireStatements) {
          if (requireStatement[1]?.startsWith(".")) {
            // is relative import.
            const key = path
              .normalize(path.join(path.dirname(keyFile), requireStatement[1]))
              .replace(/(.*?)dist-cjs\//, "./dist-cjs/");
            if (this.verbose) {
              console.log("Transitive variant file:", key);
            }

            const transitiveVariant = key.replace(/(.*?)dist-cjs\//, "").replace(/(\.js)?$/, "");

            if (!this.transitiveVariants.includes(transitiveVariant)) {
              this.variantEntries.push([key, key]);
              this.transitiveVariants.push(transitiveVariant);
            }
          }
        }
      }
    }

    this.variantExternals = [];
    this.variantMap = {};

    for (const [k, v] of this.variantEntries) {
      const prefix = "dist-cjs/";
      const keyPrefixIndex = k.indexOf(prefix);
      if (keyPrefixIndex === -1) {
        continue;
      }
      const keyRelativePath = k.slice(keyPrefixIndex + prefix.length);
      const valuePrefixIndex = String(v).indexOf(prefix);

      const addJsExtension = (file) => (file.endsWith(".js") ? file : file + ".js");

      if (valuePrefixIndex !== -1) {
        const valueRelativePath = String(v).slice(valuePrefixIndex + prefix.length);
        this.variantExternals.push(...[keyRelativePath, valueRelativePath].map(addJsExtension));
        this.variantMap[keyRelativePath] = valueRelativePath;
      } else {
        this.variantExternals.push(addJsExtension(keyRelativePath));
        this.variantMap[keyRelativePath] = v;
      }
    }

    return this;
  }