evanw/esbuild · error · Error

Unsupported input syntax

Error message

Unsupported input syntax

What it means

In the terser-test harness (scripts/terser-tests.js:210), `as_toplevel` expects the parsed input to be an `AST_BlockStatement`; if it is any other AST node type, it throws 'Unsupported input syntax'. This is internal test-tooling validation used while converting terser test fixtures into esbuild-compatible ASTs — it is not part of the esbuild library's public API.

Source

Thrown at scripts/terser-tests.js:212

// EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
// PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER BE
// LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY,
// OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
// PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
// PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR
// TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
// THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.

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

function as_toplevel(input, mangle_options) {
  if (!(input instanceof U.AST_BlockStatement))
    throw new Error("Unsupported input syntax");
  for (var i = 0; i < input.body.length; i++) {
    var stat = input.body[i];
    if (stat instanceof U.AST_SimpleStatement && stat.body instanceof U.AST_String)
      input.body[i] = new U.AST_Directive(stat.body);
    else break;
  }
  var toplevel = new U.AST_Toplevel(input);
  toplevel.figure_out_scope(mangle_options);
  return toplevel;
}

function parse_test(file) {
  var script = fs.readFileSync(file, "utf8");
  // TODO try/catch can be removed after fixing https://github.com/mishoo/UglifyJS2/issues/348
  try {
    var ast = U.parse(script, {
      filename: file
    });

View on GitHub (pinned to f6058f8364)

Solutions

1. Ensure the test fixture parses to an `AST_BlockStatement` as expected by `as_toplevel`.
2. Regenerate or restore the test fixture to the terser format the harness expects.
3. Pin the terser version to one whose test AST shape matches this harness.

Example fix

// before — fixture body is a bare expression statement at top level
// after — wrap fixture statements so they parse as AST_BlockStatement per terser test format

// In the terser test harness, validate the AST type before calling as_toplevel
const U = require('./demo/terser');
function safeAsToplevel(input) {
  if (!(input instanceof U.AST_BlockStatement)) throw new Error('Unsupported input syntax');
  return as_toplevel(input);
}

function isBlockStatement(node: any, U: any): boolean {
  return node instanceof U.AST_BlockStatement;
}

When it happens

Trigger: Running `scripts/terser-tests.js` against a terser test fixture whose source parses to a non-block top-level construct, or calling `as_toplevel` with malformed input during local test development.

Common situations: Vendoring a newer/older terser test format that changes the AST shape; editing a compress test fixture so it no longer wraps statements in a block; running the harness against an unsupported terser version.

Related errors

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

AI-assisted analysis of evanw/esbuild@f6058f8364 (2026-08-09). Data as JSON: /api/errors/2ca23a6315c5feab. Report an issue: GitHub.