# V1010 unknown_attribute

URL: /docs/errors/V1010
Markdown: /docs/errors/V1010.md

> Only these attributes exist in v0: @tool, @llm, @external, @total, @contract_test, @deprecated, @server, @test_only on items, and @trust("reason") as an expression (design §2.5).

An error from the `resolve` phase. `sakura explain V1010` prints this explanation offline.

Only these attributes exist in v0: `@tool`, `@llm`, `@external`, `@total`, `@contract_test`,
`@deprecated`, `@server`, `@test_only` on items, and `@trust("reason")` as an expression
(design §2.5). Any other attribute is unknown, any attribute but `@trust` in expression position
is rejected, and `Tool.of` takes only a function declared with `@tool` (§11.2).

Wrong:

```sakura
@pure
fn double(n: Int) -> Int { n * 2 }
```

Fixed:

```sakura
fn double(n: Int) -> Int { n * 2 }
```

## Wrong program [#wrong-program]

[`compiler/tests/ui/V1010_tool_of_lambda.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V1010_tool_of_lambda.sakura), which the compiler's ui suite runs through `sakura check`:

```sakura
import std/tool.{Tool}

pub fn tools() -> Unit { let _ = Tool.of(fn(a: Int) { a }) }
```

`sakura check --json` reports this record (pretty-printed; `$DIR` is the fixture's directory):

```json
{
  "schema_version": "1.0",
  "kind": "diagnostic",
  "id": "d:f8420bbb4dc5a025",
  "code": "V1010",
  "severity": "error",
  "phase": "resolve",
  "message": "`Tool.of` takes a function declared with `@tool`",
  "snapshot": "sha256:$SNAPSHOT",
  "symbol_id": "main::V1010_tool_of_lambda::tools",
  "spans": [
    {
      "uri": "file://$DIR/V1010_tool_of_lambda.sakura",
      "content_hash": "sha256:4a27727b2eaffc7ff21e9bc915c8c8ed6c8622f08151f2d779ae5e1d4b0915ee",
      "start_byte": 119,
      "end_byte": 144,
      "role": "primary"
    }
  ],
  "related_ids": [],
  "expected": null,
  "actual": null,
  "obligation": null,
  "counterexample": null,
  "explanation_uri": "sakura://explain/V1010",
  "fixes": []
}
```

More fixtures for this code: [`compiler/tests/ui/V1010_tool_of_untagged_function.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V1010_tool_of_untagged_function.sakura), [`compiler/tests/ui/V1010_unknown_attribute.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V1010_unknown_attribute.sakura).

## Fixed program [#fixed-program]

[`compiler/tests/ui/V1010_tool_of_lambda.fixed.sakura`](https://github.com/icantcodefyi/sakuralang/blob/master/compiler/tests/ui/V1010_tool_of_lambda.fixed.sakura), which `sakura check` accepts with no diagnostics:

```sakura
import std/tool.{Tool}

@tool("Doubles a number.")
pub fn double(a: Int) -> Int { a * 2 }

pub fn tools() -> Unit { let _ = Tool.of(double) }
```