{"record":{"id":"63dba0ac897fa417","repo":"diesel-rs/diesel","slug":"unexpected-end-of-input-expected-parentheses-help","errorCode":null,"errorMessage":"unexpected end of input, expected parentheses\nhelp: the correct format looks like `#[diesel({BELONGS_TO_NOTE})]`","messagePattern":"unexpected end of input, expected parentheses\nhelp: the correct format looks like `#\\[diesel\\((.+?)\\)\\]`","errorType":"validation","errorClass":"syn::Error","httpStatus":null,"severity":"error","filePath":"diesel_attribute_parser/src/deprecated/belongs_to.rs","lineNumber":11,"sourceCode":"use syn::parse::{ParseStream, Result};\nuse syn::token::Comma;\nuse syn::{Ident, LitStr, parenthesized};\n\nuse crate::deprecated::utils::parse_eq_and_lit_str;\nuse crate::notes::BELONGS_TO_NOTE;\nuse crate::parsers::BelongsTo;\n\npub fn parse_belongs_to(name: Ident, input: ParseStream) -> Result<BelongsTo> {\n    if input.is_empty() {\n        return Err(syn::Error::new(\n            name.span(),\n            format!(\n                \"unexpected end of input, expected parentheses\\n\\\n                 help: the correct format looks like `#[diesel({BELONGS_TO_NOTE})]`\"\n            ),\n        ));\n    }\n\n    let content;\n    parenthesized!(content in input);\n\n    let parent = if content.peek(Ident) {\n        let name: Ident = content.parse()?;\n\n        if name == \"parent\" {\n            let lit_str = parse_eq_and_lit_str(name, &content, BELONGS_TO_NOTE)?;\n            lit_str.parse()?\n        } else {","sourceCodeStart":1,"sourceCodeEnd":29,"githubUrl":"https://github.com/diesel-rs/diesel/blob/6fa6ed01b24b24248ab2a611698d0a7c6a2e9120/diesel_attribute_parser/src/deprecated/belongs_to.rs#L1-L29","documentation":"The deprecated `#[diesel(belongs_to(...))]` attribute parser found the attribute name but no parenthesized argument list following it. It emits a `syn::Error` at the attribute name's span with a help note showing the expected format.","triggerScenarios":"Writing `#[diesel(belongs_to)]` with no parentheses/arguments on a struct or field, then running the diesel derive macros.","commonSituations":"Copying old association examples, deleting the argument by mistake, or migrating associations between models and leaving the attribute empty.","solutions":["Add the parenthesized target table, e.g. `#[diesel(belongs_to(User))]`","Add `foreign_key = \"...\"` inside the parentheses if the FK column is not the default","Consult the current diesel association docs; `belongs_to` syntax changed across major versions"],"exampleFix":"// before\n#[diesel(belongs_to)]\npub struct Post { user_id: i32 }\n// after\n#[diesel(belongs_to(User))]\npub struct Post { user_id: i32 }","handlingStrategy":"validation","validationCode":"// compile-time: always pass arguments\n// #[diesel(belongs_to(User, foreign_key = \"user_id\"))]","typeGuard":null,"tryCatchPattern":null,"preventionTips":["Never write a diesel attribute without its parentheses","Verify attribute syntax against the diesel version you compile with"],"tags":["rust","proc-macro","diesel-derive","attribute-syntax"],"backgroundTag":"invalid-argument-format","analyzedSha":"6fa6ed01b24b24248ab2a611698d0a7c6a2e9120","analyzedAt":"2026-09-07T01:50:13.074Z","contentChangedAt":"2026-09-07T01:50:13.074Z","schemaVersion":2},"datasetVersion":"2026-09-16T09:17:16.951Z"}