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fixes #25407; SIGSEGV when compiling when with typedesc #25551

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fixes #25407; SIGSEGV when compiling when with typedesc #25551

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2a8e4dd
fixes #25407; SIGSEGV when compiling when with typedesc
ringabout Feb 25, 2026
d05e936
Merge branch 'devel' into pr_when_typ
ringabout Apr 17, 2026
7867200
normalizeTypedescMacroResult
ringabout Apr 17, 2026
790df93
oops
ringabout Apr 17, 2026
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23 changes: 21 additions & 2 deletions compiler/sem.nim
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Original file line number Diff line number Diff line change
Expand Up @@ -454,6 +454,25 @@ proc resetSemFlag(n: PNode) =
for i in 0..<n.safeLen:
resetSemFlag(n[i])

proc normalizeTypedescMacroResult(c: PContext, n: PNode): PNode =
result = n
if result.kind == nkStmtList:
result.transitionSonsKind(nkStmtListType)

# Resolve surviving compile-time branches so later passes don't walk
# unevaluated type AST for a typedesc expression.
while true:
if result.kind == nkWhenStmt:
result = semWhen(c, result, false)
if result.kind == nkStmtList:
result.transitionSonsKind(nkStmtListType)
elif result.kind == nkStmtListType and result.len > 0 and result[^1].kind == nkWhenStmt:
result[^1] = semWhen(c, result[^1], false)
Comment on lines +465 to +470
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Copilot AI Apr 17, 2026

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The while true loop can become infinite when semWhen(c, ..., false) returns the original nkWhenStmt unchanged (e.g. for when nimvm, where semWhen intentionally returns the when node for codegen, or when cannotResolve in generic contexts leads to semGenericStmt returning an nkWhenStmt). Add a termination guard (e.g. compare with the pre-call node and/or break when the result is still an nkWhenStmt after semWhen) so normalization only repeats when the when was actually reduced to a branch AST.

Suggested change
if result.kind == nkWhenStmt:
result = semWhen(c, result, false)
if result.kind == nkStmtList:
result.transitionSonsKind(nkStmtListType)
elif result.kind == nkStmtListType and result.len > 0 and result[^1].kind == nkWhenStmt:
result[^1] = semWhen(c, result[^1], false)
if result.kind == nkWhenStmt:
let prev = result
result = semWhen(c, result, false)
if result == prev or result.kind == nkWhenStmt:
break
if result.kind == nkStmtList:
result.transitionSonsKind(nkStmtListType)
elif result.kind == nkStmtListType and result.len > 0 and result[^1].kind == nkWhenStmt:
let prev = result[^1]
result[^1] = semWhen(c, result[^1], false)
if result[^1] == prev or result[^1].kind == nkWhenStmt:
break

Copilot uses AI. Check for mistakes.
if result[^1].kind == nkStmtList:
result[^1].transitionSonsKind(nkStmtListType)
else:
break

proc semAfterMacroCall(c: PContext, call, macroResult: PNode,
s: PSym, flags: TExprFlags; expectedType: PType = nil): PNode =
## Semantically check the output of a macro.
Expand Down Expand Up @@ -484,15 +503,15 @@ proc semAfterMacroCall(c: PContext, call, macroResult: PNode,
# More restrictive version.
result = semExprWithType(c, result, flags, expectedType)
of tyTypeDesc:
if result.kind == nkStmtList: result.transitionSonsKind(nkStmtListType)
result = normalizeTypedescMacroResult(c, result)
var typ = semTypeNode(c, result, nil)
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if typ == nil:
localError(c.config, result.info, "expression has no type: " &
renderTree(result, {renderNoComments}))
result = newSymNode(errorSym(c, result))
else:
result.typ = makeTypeDesc(c, typ)
#result = symNodeFromType(c, typ, n.info)
#result = symNodeFromType(c, typ, n.info)
else:
if s.ast[genericParamsPos] != nil and retType.isMetaType:
# The return type may depend on the Macro arguments
Expand Down
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