evanw/esbuild · error · Error

Unsupported input syntax

Error message

Unsupported input syntax

What it means

Thrown by to_toplevel() in scripts/uglify-tests.js:470. After parsing the test's `input:` value, the harness requires it to be an AST_BlockStatement (a brace-enclosed block). If the parsed input is any other node type (a single expression, a declaration, etc.), this error is raised before scope analysis.

Source

Thrown at scripts/uglify-tests.js:470

    });
    block.walk(tw);
    return test;
  }
}

function run_code(code, toplevel) {
  const sandbox = require(path.join(uglifyDir, 'test', 'sandbox'));

  var result = sandbox.run_code(code, toplevel);
  return typeof result == "string" ? result.replace(/\u001b\[\d+m/g, "") : result;
}

function tmpl() {
  return U.string_template.apply(null, arguments);
}

function to_toplevel(input, mangle_options) {
  if (!(input instanceof U.AST_BlockStatement)) throw new Error("Unsupported input syntax");
  var directive = true;
  var offset = input.start.line;
  var tokens = [];
  var toplevel = new U.AST_Toplevel(input.transform(new U.TreeTransformer(function (node) {
    if (U.push_uniq(tokens, node.start)) node.start.line -= offset;
    if (!directive || node === input) return;
    if (node instanceof U.AST_SimpleStatement && node.body instanceof U.AST_String) {
      return new U.AST_Directive(node.body);
    } else {
      directive = false;
    }
  })));
  toplevel.figure_out_scope(mangle_options);
  return toplevel;
}

View on GitHub (pinned to f6058f8364)

Solutions

1. Wrap the input body in `{ ... }` so it parses as a block statement.
2. Verify the input still reproduces the original bug after wrapping.

Example fix

// before
input: var a = 1; console.log(a);

// after
input: { var a = 1; console.log(a); }

function isBlockInput(parsedInput) {
  return parsedInput instanceof U.AST_BlockStatement;
}

const isBlockStatement = (node) => node instanceof U.AST_BlockStatement;

try { to_toplevel(input, mangle); }
catch (e) {
  if (/Unsupported input syntax/.test(e.message)) console.error('Wrap the input field body in { ... }');
  throw e;
}

When it happens

Trigger: An uglify test's `input:` field is not wrapped in curly braces, so it parses to something other than an AST_BlockStatement. For example `input: var a = 1;` instead of `input: { var a = 1; }`.

Common situations: Contributor writes an input as a bare statement or omits the enclosing braces required by the compress-test DSL.

Related errors

• Duplicated test name "${name}" in ${file}
• Can't understand test file {file} [{line},{col}] {code}
• Should be array of strings
• Should be string or array of strings
• Can't understand test file {file} [{line},{col}] {code}

AI-assisted analysis of evanw/esbuild@f6058f8364 (2026-08-09). Data as JSON: /api/errors/ddc32039162b11bf. Report an issue: GitHub.