[Audit-Medium] CodeBlock.Write silently drops whitespace-only strings

[pepone]

AI-generated audit finding — this issue was opened from an automated security/correctness audit. It has not been triaged by a human yet; verify the reasoning, reproducibility, and severity before acting on it.

Medium: CodeBlock.Write silently drops whitespace-only strings

Affected code:

• src/ZeroC.CodeBuilder/CodeBlock.cs:96-102 — Write guards with !string.IsNullOrWhiteSpace(value) and skips the append otherwise
• src/ZeroC.CodeBuilder/CodeBlock.cs:49 — AddBlock relies on Write($"\n{block}\n")
• src/ZeroC.CodeBuilder/CodeBlock.cs:106 — WriteLine relies on Write($"{value}\n")

Description:

Any string composed entirely of whitespace — spaces, tabs, newlines, or any combination — is silently discarded by Write. Two concrete consequences:

1. WriteLine("") is a no-op. A caller that intends to emit a blank line (between attribute declarations, between comment blocks, etc.) gets nothing. The only way to force a blank line is to call Write("\n\n") which itself is whitespace and also gets dropped.

2. AddBlock of an empty CodeBlock emits nothing. $"\n{block}\n" where block renders as "" is just "\n\n", which is whitespace and therefore discarded. That is probably intentional ("don't add a block-shaped gap for an empty contribution"), but it is invisibly entangled with the more surprising behavior of blank-line emission being impossible.

The guard seems designed to suppress no-op calls, but it is too aggressive: it equates "whitespace-only input" with "no input at all". Formatting intent that involves whitespace can't be expressed.

Combined with the normalization in ToString (see finding #3), the library's contract around blank lines is opaque: callers can't reliably predict how many blank lines will appear between two blocks.

Impact:

• Generators that want to control vertical whitespace have no reliable mechanism.
• A one-line change to add a blank line (sb.WriteLine("")) silently does nothing, which is a confusing debugging experience.

Recommendation:

• Change the guard to value is not null, or drop the guard entirely. The StringBuilder itself handles empty-string appends efficiently.
• If the guard is kept for empty-string efficiency, require value.Length == 0 rather than IsNullOrWhiteSpace.
• Document the AddBlock(emptyBlock) behavior explicitly.

Severity: Medium.

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Source report: src-ZeroC.CodeBuilder-audit-2026-04-14.md (finding ``CodeBlock.Write silently drops whitespace-only strings)

Severity (auditor-assigned): Medium

[externl]

This behavior is by design to control and not have to worry about whitespace when generating code; allowing us to write things like:

code.WriteLine("{");
code.WriteLine($"    {bodyContent.Indent()}");
code.WriteLine("}");

without having to worry about whitespace (we don't want an empty line between { and } if bodyContent is empty).

The only way to force a blank line is to call Write("\n\n") which itself is whitespace and also gets dropped.

Indeed, You can't just write an empty line.

callers can't reliably predict how many blank lines will appear between two blocks.

Not true. We explicitly always have a single blank line between two code blocks.

Additionally, you also can't have more than once blank line between two non-whitespace lines in a CodeBlock. For example:

{{
    {foo}

    {bar}
}}";