Error: Missing newline after argument: HCL syntax error on one line

TL;DR

Two arguments ended up on one line, or you used non-HCL syntax (like a JavaScript function call) inside a .tf file. HCL wants one argument per line. Split them, replace JS-isms with HCL natives (jsonencode), and run terraform fmt.

The error

Error: Missing newline after argument

  on main.tf line 200:
  200: event_pattern = JSON.stringify({

Steps to fix

1. Open the flagged line. Look for two arguments jammed together, or a function call from another language (JSON.stringify, etc.).

• Expected: you spot the offending syntax.

1. Rewrite in HCL: one argument per line, HCL-native functions:

   event_pattern = jsonencode({
     source = ["my.service"]
   })

• Expected: no foreign syntax remains.

1. Run terraform fmt then terraform validate.

• Expected: Success! The configuration is valid.

When to use this

• terraform validate/plan fails with Missing newline after argument after editing or pasting config, especially config translated from another language.

When NOT to use this

• Invalid character (e.g. ;) is the sibling error for characters HCL rejects outright. If the line looks fine, check for invisible characters from copy-paste.

Compatibility

• All Terraform versions; HCL2 syntax rules are stable.

Root cause

HCL separates block arguments with newlines. Pasting multi-argument snippets onto one line, or transliterating JavaScript/Python expressions directly into .tf files, produces tokens the parser cannot split into separate arguments.

Edge cases

• Heredocs (<<EOT) containing code from other languages are fine; the error only applies to HCL outside strings.
• terraform fmt will not fix this; it only formats valid syntax. Fix the syntax first, then format.