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A BodyFactory that throws leaves a half-written member, and inside a class the closing brace lands on it: public void M()} #176
Description
What's wrong
Method, constructor, operator and property templates write their doc comment, attributes and signature first. Only then do they call the user's BodyFactory/ExpressionBodyFactory, through TemplateRendering.RenderFragment (WriteBody at TemplateRendering.cs#L281, WriteExpressionBody at #L328). If the callback throws, the header is already in the buffer.
Inside a class, the using Scope in ClassTemplate.cs#L129 still writes } while the exception unwinds, and that brace lands on the unfinished line.
Repro (at 21ac04c)
cb.AddClass(new ClassTemplate { Name = "C", Members = {
new FieldTemplate { Name = "a", Type = "int" },
new MethodTemplate { Name = "M", Type = "void", Keywords = { "public" },
BodyFactory = _ => throw new InvalidOperationException("no body") },
new FieldTemplate { Name = "b", Type = "int" } } });The exception propagates, and the buffer then holds:
class C
{
int a;
int b;
public void M()}
A standalone property with a throwing ExpressionBodyFactory and a summary leaves /// <summary>s</summary> followed by int P.
Why it matters
The callback is user code: a generator walking its model can throw on a malformed input. The templates promise elsewhere that when they throw, "nothing is written" and a caller that catches the exception can keep using the CodeBlocker. Here the caller is left with a buffer they can't recover. If they log the error and emit the rest of the file (common in source generators that report a diagnostic and continue), the file doesn't compile.
This is related to #164 and its open PR #169, but it's a different case. Those pre-check things the library itself rejects, before anything is written. Validate() never runs user callbacks, so a throwing callback is still unhandled after #169.
Suggested fix / acceptance criteria
- The callbacks already render into a separate buffer (
RenderFragment). Render the body, expression body and accessor bodies before writing the member header, then write the header and splice in the pre-rendered text. - For
ClassTemplate, render the members into a fragment before writing the declaration and opening theScope, so a member failure leaves nothing of the class behind. - Tests: in both repros above the exception propagates and
cb.ToString()is unchanged from before the call.
Activity
matt-edmondson commentedon Nov 3, 2026
Triage
Category: Bug
Priority: Medium. The output is corrupted, but only on the exception path. A caller only hits it if they catch an exception thrown by their own
BodyFactory/ExpressionBodyFactoryand then keep writing to the sameCodeBlocker. That is a real pattern in source generators, and it breaks the library's "nothing is written when a template throws" promise. Normal successful generation is unaffected.Area / suggested assignment: Templates rendering pipeline (
TemplateRendering.WriteBody/WriteExpressionBody,ClassTemplate.WriteTo). This is the maintainer of the recent "check before writing" series.Duplicates / in-progress check
Validate()never runs callbacks.ClassTemplate.WriteTo, so they will conflict. Land Check a class's members before writing any of it [patch] #169 first, then render members into a fragment on top of it.int P => ;/get => ;(CS1525), the output Validate says it prevents #175) addsTemplateRendering.RenderExpression, which pre-renders the expression body before writing. That is most of what this issue needs for the expression-body case. Build on Refuse an expression body that writes no expression, before writing [patch] #178 rather than in parallel with it.get => ;#142 (closed) dealt with the same "half a declaration before throwing" family for unknown kinds.Next steps
Scope.cb.ToString()is unchanged after the exception.Generated by Claude Code
matt-edmondson commentedon Nov 4, 2026
Triage
The prerequisites from the earlier triage have landed: #169 and #178 are both merged. This is still not actionable yet, because open PR #182 ("Drop the blank lines around a braced member body") edits
TemplateRendering.cs, the same body-writing path this fix has to restructure. The two would conflict.Scope.TemplateRendering.Generated by Claude Code