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0135 - A call and a failed property read are located where V8 locates them

Date: 2026-10-10 Area: parser, bytecode compiler, diagnostics Related: ADR 0014, ADR 0122, ADR 0131

Context

A call expression's position is its call site. Both executors report it in a stack frame that is making the call, in an audit event and in a PermissionDenied error for that call. The parser put a call at its opening parenthesis, and a dotted member expression at its .. V8 puts inner(obj) at inner and obj.x at x, so a GocciaScript trace and Node's disagreed in the column for nearly every frame (#1494).

ECMA-262 says nothing about where a call or a property read is. The bytecode compiler also located a failed read through the line map, where an expression's entry precedes the code of its operands, so the load of a.b.c was located at a.

Decision

The parser gives each node the position V8 reports, so both executors and every consumer of a call site agree:

  • A call whose ( follows an identifier token is located at that token: the callee of f(), super of super(), or the property name of a.b(). Any other call is located at its (. This is V8's rule, which keys on the token before the (: a reserved-word property (p.catch()), a private name (this.#m()), a parenthesized callee and an optional call (f?.()) all stay at the (.
  • new is located at the new keyword, whatever its callee (new ns.Widget() had been located at Widget).
  • A dotted member is located at its property name; a computed member stays at its [, and a private member at its ..

The bytecode compiler gives the instruction that loads a member's property the member's position, and restores the line-map entry in effect before it for the instructions that follow, so nothing else in the line map moves. The interpreter stamps a failed read at the member rather than at the base of its chain.

Consequences

  • Stack traces, the --> header and its caret, --output=json, audit events and PermissionDenied move from a call's ( to its callee's name where V8 puts it there.
  • The instructions the compiler emits do not change; the line map gains up to two entries for each property read whose object needed code of its own. An entry at the same PC as the entry before it replaces that entry, which no lookup could reach, so the line maps end up smaller than before overall.
  • Private-member reads and property writes keep their existing positions, which still differ from V8.