HCL synth doesn't escape backslashes in strings: the default local backend path on Windows produces invalid cdk.tf #562

Expected Behavior

HCL synth escapes backslashes in string literals, so a Windows path renders as "C:\\Users\\...".

Actual Behavior

Backslashes are copied through unchanged. Every HCL synth on Windows that uses the default local backend produces a cdk.tf that won't init. LocalBackend defaults to path.join(process.cwd(), ...) (local-backend.ts:23), which is an absolute backslash path on Windows:

terraform {
backend "local" {
path = "C:\Users\me\project\terraform.s.tfstate"
}
}

Error: Invalid escape sequence

  on cdk.tf line 6, in terraform:
   6: path = "C:\Users\me\project\terraform.s.tfstate"

The \U escape sequence must be followed by eight hexadecimal digits.

(Path shortened.) Terraform 1.14.3 and OpenTofu 1.12.6 on Windows 11 both reject it at init. The JSON output for the same stack is valid.

Steps to Reproduce

On Windows, with SYNTH_HCL_OUTPUT=true, synthesize any stack without an explicit backend and run terraform init -backend=false in the stack directory. I reproduced this by running the library directly on upstream/main, not through the CLI.

Any string attribute containing a backslash hits the same bug, not just the backend path. A path ending in \ leaves the string unterminated.

Cause

String literals go through escapeQuotes (render.ts:10-16, used at L46 and L589). That function only escapes ", and it skips any " that follows a backslash.

Possible Solutions

Escape \ before " in literal strings, which is what JSON.stringify does. The (?<!\\) lookbehind would then have to go too, because once backslashes are escaped, a backslash before a quote is no longer a sign that the quote is already escaped. Strings containing ${ take a separate path and need the same treatment inside the literal parts.

Upstream cdktf Issue

None found.

References

• synth --hcl emits invalid HCL for string attributes containing literal double quotes #468 / fix(lib): escape quotes in HCL string expressions #501: quotes in HCL string expressions (same function)
• Map keys containing quotes, backslashes, ${...}, or %{...} are not escaped, producing invalid Terraform #341 (closed) and tfExpression/HCL renderer: object keys are rendered into expressions without escaping #350: escaping in map and object keys
• fix(lib): HCL synth corrupts or drops core blocks (terraform{} extras, top-level overrides, lifecycle conditions) #313: other HCL synth defects
• testing: validate both JSON and HCL synth output in core unit tests, not just JSON snapshots #563: validating HCL output in unit tests