SIFR-OWN-0002: Conflicting borrow.

SIFR-OWN-0002 belongs to the Ownership and borrowing diagnostic family. It means: conflicting borrow.

Why It Happens

The ownership model would be violated. Move values only once, keep borrows scoped, and cross task/channel/IPC boundaries only with owned values that satisfy the required safety traits.

Use sifr --explain SIFR-OWN-0002 locally to see the renderer’s exact message template and any machine-applicable suggestions for the compiler version you are running.

Erroneous Code

The same storage cannot participate in conflicting reads, moves, or mutable borrows. Most often this happens when an overlapping field read, shared borrow, mutable borrow, or owned move occurs in the same call as a mutable receiver or mutable argument. It can also happen when a second anext() advance starts before the first pending advance has been awaited.

class Buffer:
    values: list[int]

    def replace_from(self, own other: Buffer) -> None:
        self.values = other.values

def replace_with_self(mut buffer: Buffer) -> None:
    buffer.replace_from(buffer)

How To Fix It

Use a disjoint place for every other argument while a mutable receiver or argument is active. If an argument only needs a value derived from the same place, snapshot that value in a local before the call. For example, rewrite values.append(len(values)) as:

count = len(values)
values.append(count)

For async generators, await the pending anext() result before starting the next advance. For example, this starts a second advance while the first one still holds the generator:

agen = numbers()
first = anext(agen)
second = anext(agen)

Await each advance before starting the next one:

agen = numbers()
first = await anext(agen)
second = await anext(agen)

Fixed Code

class Buffer:
    values: list[int]

    def replace_from(self, own other: Buffer) -> None:
        self.values = other.values

def replace(mut target: Buffer, own source: Buffer) -> None:
    target.replace_from(source)

Details

Field	Value
Code	`SIFR-OWN-0002`
Family	`OWN`
Severity	Error
Stability	stable
Owner	`sifr_lowering::lower`
Representative fixture	`crates/sifr/tests/e2e/fail/double_mut_borrow.sifr`

See the Error Codes index for the complete catalog.

​Why It Happens

​Erroneous Code

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Why It Happens

Erroneous Code

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Fixed Code

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