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Cyclic initialization compiles with -Yexplicit-nulls and -Ysafe-init #11262

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crater2150 opened this issue Jan 31, 2021 · 1 comment
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Cyclic initialization compiles with -Yexplicit-nulls and -Ysafe-init #11262

crater2150 opened this issue Jan 31, 2021 · 1 comment
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area:initialization itype:bug

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@crater2150
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crater2150 commented Jan 31, 2021 •
edited by liufengyun

Compiler version

3.0.0-M3-bin-20201216-c8fb1fa-NIGHTLY-git-c8fb1fa

Minimized code

object A { val x: String = B.y }
object B { val y: String = A.x }

Output

Compiled with both -Yexplicit-nulls and -Ysafe-init, both fields are null:

A.x == null
B.y == null

Expectation

I expected this not to compile. I'm not sure if detecting such cycles is in scope for -Ycheck-init, but the documentation for explicit nulls suggests that -Ycheck-init catches the unsoundness caused by null in initialization.
@liufengyun liufengyun self-assigned this Jan 31, 2021
@liufengyun liufengyun linked a pull request Jan 31, 2021 that will close this issue
Check safe initialization of global objects #10550
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@liufengyun liufengyun mentioned this issue Apr 16, 2021
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@liufengyun liufengyun mentioned this issue Jun 7, 2021
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@liufengyun liufengyun mentioned this issue Oct 8, 2022
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@liufengyun liufengyun mentioned this issue Feb 20, 2023
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liufengyun added a commit that referenced this issue Jun 16, 2023
@liufengyun
Check safe initialization of static objects (#16970)
5caa6aa 
The problem is illustrated by the example below:

``` Scala
class Foo(val opposite: Foo)
case object A extends Foo(B)     // A -> B
case object B extends Foo(A)     // B -> A
```
The check aims to be simple for programmers to understand, expressive,
fast, and sound.

The check is centered around two design ideas: (1) initialization-time
irrelevance; (2) partial ordering.

The check enforces the principle of _initialization-time irrelevance_,
which means that the time when a static object is initialized should not
change program semantics. For that purpose, it enforces the following
rule:

> **The initialization of a static object should not directly or
indirectly read or write mutable state owned by another static object**.

This principle not only puts the initialization of static objects on a
solid foundation but also avoids whole-program analysis.

Partial ordering means that the initialization dependencies of static
objects form a directed-acyclic graph (DAG). No cycles with length
bigger than 1 allowed --- which might lead to deadlocks in the presence
of concurrency and strong coupling & subtle contracts between objects.

Related Issues:

#16152
#9176
#11262
scala/bug#9312
scala/bug#9115
scala/bug#9261
scala/bug#5366
scala/bug#9360
@liufengyun
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This can now be checked with the experimental option: -Ysafe-init-global.

@liufengyun liufengyun changed the title Cyclic initialization compiles with -Yexplicit-nulls and -Ycheck-init Cyclic initialization compiles with -Yexplicit-nulls and -Ysafe-init Jul 15, 2023
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