ruby-core

Issue #9725 has been reported by Charles Nutter.

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Feature #9725: Do not inspect NameError target object unless verbose
https://bugs.ruby-lang.org/issues/9725

* Author: Charles Nutter
* Status: Open
* Priority: Normal
* Assignee: 
* Category: 
* Target version: 
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At least once every few months, we get an error report of JRuby raising a memory error where MRI does not due to NameError's Message object holding a reference to an object that's too large to inspect. I propose that this inspection of the target object should only be done in verbose mode.

Background:

NameError is raised when a variable-like method call fails to find a defined method. The resulting exception is created with a hidden NameError::Message that holds the object in which the method could not be found.

When name error needs to render its message, such as when it bubbles out or when #message is called, it does to_str on the NameError::Message, which ends up inspecting the target object. If this object's inspect output is large (or infinite) it can end up consuming a large amount of memory.

Problems:

* If the amount of memory required to render a NameError exceeds available memory, a very confusing and misleading memory error can be raised instead.
* If the target object is considered sensitive data, it will end up bubbling out through potentially untrustworthy code. It is an encapsulation flaw, basically.
* A NameError that gets held in memory will also prevent GC of the object it references.

Solutions:

* NameError should not capture the target object.
* NameError should build a message based on the target object *at creation time*, and only include information useful to indicate the type of object.
* (Optional) If verbose mode is set, NameError can just do what it does now.



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