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An expression body that writes only a comment or directives still renders int P => ;// TODO (CS1525): the #175 guard checks only for blank lines #184
Description
What happens
#178 (for #175) refuses an expression body whose callback writes nothing. A callback that writes only a comment, or only preprocessor directives, gets through and produces the same => ;:
| Input | Output |
|---|---|
ExpressionBodyFactory = b => b.WriteLine("// TODO") |
int P => ;// TODO |
Getter = AccessorTemplate.Expression(b => b.WriteLine("// TODO")) |
get => ;// TODO |
ExpressionBodyFactory = b => { b.WriteLine("#if DEBUG"); b.WriteLine("#endif"); } |
int P =>#if DEBUG#endif; |
All three fail with CS1525 (invalid expression term ;). Reproduced against main @ aa7ca53, and the generated code was compiled to confirm the errors.
Why
RenderExpression (CodeBlocker/Templates/TemplateRendering.cs:341) throws only when every line is whitespace (lines.All(string.IsNullOrWhiteSpace)). When no line holds code, FindTerminatedLine (:429-446) stops at the first line, and Terminate (:527-537) puts the semicolon in front of the comment.
A placeholder like // TODO as the whole body is a common pattern while scaffolding generated code, so this is easy to hit.
Suggested fix
In RenderExpression, also throw when !HasCode(lines), using the existing HasCode / FindCodeEnds helpers. That gives a body made only of comments or directives the same InvalidOperationException and message as an empty one.
Acceptance criteria
- All three inputs above throw the An expression-body callback that writes nothing renders
int P => ;/get => ;(CS1525), the output Validate says it prevents #175InvalidOperationExceptioninstead of writing=> ;. - An expression whose last line has a trailing comment (An expression body whose last line ends in a // comment gets its semicolon inside the comment:
public int P => x // note;does not compile (CS1002) #144) and one wrapped in#if/#endifaround real code (An expression body containing #if/#else/#endif rendersint P => #if DEBUGand#endif;, which doesn't compile #158) still render as they do today. - Ideally the check runs from
Validate(), so nothing is written first. See the companion issue on the empty-body check bypassing validation.
Activity
matt-edmondson commentedon Nov 5, 2026
Triage
// TODOplaceholder is a common scaffolding pattern, so it is easy to hit.TemplateRendering.RenderExpression,HasCode/FindCodeEnds!HasCode(lines)). Do it together with A class with an empty expression-bodied property is still written with its closing brace, minus that member and everything after it (#164 again, since #178) #183 so the check runs fromValidate().int P => ;/get => ;(CS1525), the output Validate says it prevents #175/Refuse an expression body that writes no expression, before writing [patch] #178 and is the companion of A class with an empty expression-bodied property is still written with its closing brace, minus that member and everything after it (#164 again, since #178) #183. A method body made only of a/* block comment */is written as no body:void M() /* nothing to do */(CS1002), unlike the//form fixed in #157 #185 handles the/* */variant through the sameHasCodepath. No open PR covers it.Generated by Claude Code