feature flag redaction poc

redact.js

import * as recast from "recast";

// consequent to omit code
const redactedConsequent = recast.parse`\
if (false) {
    // REDACTED
}
`.program.body[0].consequent;

// a source code file
const code = `\
if (FOO) {
    console.log("FOO");
} else {
    console.log("NOT FOO");
}

if (BAR) {
    console.log("BAR");
} else {
    console.log("NOT BAR");
}

if (BAZ) {
    console.log("BAZ");
} else {
    console.log("NOT BAZ");
}

if (UNKNOWN) {
    console.log("UNKNOWN");
}`;

// which flags are on or off
const FEATURE_FLAGS = {
  FOO: false,
  BAR: true,
  BAZ: false,
};

// get ast
const ast = recast.parse(code);

// loop through ast body, redact consequents where the flag is disabled
ast.program.body = ast.program.body.map((node) => {
  // redact consequents where the flag is disabled
  if (node.type === "IfStatement") {
    if (FEATURE_FLAGS[node.test.name] === false) {
      node.consequent = redactedConsequent;
    }
  }
  return node;
});

console.log(FEATURE_FLAGS);
console.log(recast.print(ast).code);

/* Output:
{ FOO: false, BAR: true, BAZ: false }
if (FOO) {
    // REDACTED
} else {
    console.log("NOT FOO");
}

if (BAR) {
    console.log("BAR");
} else {
    console.log("NOT BAR");
}

if (BAZ) {
    // REDACTED
} else {
    console.log("NOT BAZ");
}

if (UNKNOWN) {
    console.log("UNKNOWN");
}
*/