> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sifr.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Pre-v1 breaking changes

> The canonical language, library, package, tooling, and installation contracts selected before Sifr 1.0.

Sifr does not support source compatibility with unpublished pre-v1 builds.
Update old projects to the contracts on this page.

## Exact integers

Use `int` for arbitrary-precision integer values. Use an explicit fixed-width
integer type only when a data boundary requires that representation.

The former separate `bigint` spelling and its dedicated diagnostics are not
supported.

## Standard library names

Use the names in the [compiled public API](/stdlib/public-api). Important
changes include:

* Use `math.fabs`, `math.pow`, and the built-in `min`, `max`, and `round`.
* Use `random.randint`, `random.random`, and `random.uniform`.
* Use `platform.system`, `platform.machine`, `platform.node`, `platform.release`, `platform.version`, and `platform.processor`.
* Use `time.time`, `time.strftime`, `sys.argv`, `sys.exit`, and the documented `sifr.env` names.
* Use `json.loads`, `json.dumps`, `tomllib.loads`, `fnmatch.filter`, `html.escape`, and `html.unescape`.
* Use `calendar.isleap`, `calendar.weekday`, `calendar.monthrange`, `url.parse`, and `url.build`.
* Use first-class `bytes` methods and bytes-native hashing. Encode text before hashing it.
* Use first-class `set[T]` operations. `heapq` and `bisect` now mutate their input collections.

Each operation has one public name. Private `_sifr.*` implementation names are
not public imports.

## Method receivers

Receiver spelling is explicit:

| Source spelling | Meaning                | Field mutation |
| --------------- | ---------------------- | -------------- |
| `self`          | shared borrow          | rejected       |
| `mut self`      | mutable borrow         | allowed        |
| `own self`      | owned receiver         | rejected       |
| `own mut self`  | owned mutable receiver | allowed        |

The compiler does not infer receiver mutability from the method body.

## Packages and source layout

Use one optional `[source].root` value. It defaults to `src`. The `[source]`
table does not accept other fields.

Do not use multiple source roots, manifest export lists, or Sifr manifest
binary tables. Declare library exports in `src/__init__.sifr`. Put applications
in `src/main.sifr` or `src/bin/*.sifr`.

Package import resolution preserves unresolved, ambiguous, access-error, and
fatal results. Tools must not collapse these results into an optional path.

## Installation layout

A managed standalone installation uses one relationship:

```text theme={null}
<sysroot>/bin/sifr
<sysroot>/install.json
<sysroot>/sysroot.toml
```

The preferred sysroot is `$HOME/.sifr`. Flat binary and receipt layouts are not
managed installations.

## Diagnostics and verification

Import diagnostics use the current `SIFR-IMPORT-*` codes. Removed workspace
codes and migration-only replacement messages are not emitted.

Verification profiles use schema version 2 and structured result JSON. Passing
end-to-end fixtures use Sifr `assert` statements for runtime expectations.

## Compiler service contracts

Compiler services receive a source provider or use a captured
`WorkspaceSession`. Lower layers do not open disk-backed projects through
paired convenience wrappers.

Code generation uses structured Rust types. Unsupported source types produce a
compiler diagnostic instead of a string-rendered Rust type fallback.

## Retained compatibility

External protocol and current product behavior remain supported. Examples
include LSP UTF-16 defaults, Cargo metadata, DLPack capsules, supported IPC
negotiation, cancellation cleanup, configuration defaults, locale fallback,
supported external formats, and host portability.

These retained contracts do not restore old Sifr syntax, names, schemas, or
layouts.