t

{"record":{"id":"c5e0dfd4ed8f7059","repo":"swc-project/swc","slug":"somethingseenwhensomethingopen","errorCode":"SomethingSeenWhenSomethingOpen","errorMessage":"Start tag \"{tag_name}\" seen but an element of the same type was already open","messagePattern":"Start tag \"(.+?)\" seen but an element of the same type was already open","errorType":"validation","errorClass":"Error","httpStatus":null,"severity":"warning","filePath":"crates/swc_html_parser/src/parser/mod.rs","lineNumber":1955,"sourceCode":" }\n\n let popped = self\n .open_elements_stack\n .pop_until_tag_name_popped(&[\"template\"]);\n\n self.update_end_tag_span(popped.as_ref(), token_and_info.span);\n self.active_formatting_elements.clear_to_last_marker();\n self.template_insertion_mode_stack.pop();\n self.reset_insertion_mode();\n }\n }\n // A start tag whose tag name is \"head\"\n //\n // Any other end tag\n //\n // Parse error. Ignore the token.\n Token::StartTag { tag_name, .. } if tag_name == \"head\" => {\n self.errors.push(Error::new(\n token_and_info.span,\n ErrorKind::SomethingSeenWhenSomethingOpen(tag_name.clone()),\n ));\n }\n Token::EndTag { tag_name, .. } => {\n self.errors.push(Error::new(\n token_and_info.span,\n ErrorKind::StrayEndTag(tag_name.clone()),\n ));\n }\n // Anything else\n //\n // Pop the current node (which will be the head element) off the stack of open\n // elements.\n //\n // Switch the insertion mode to \"after head\".\n //\n // Reprocess the token.","sourceCodeStart":1937,"sourceCodeEnd":1973,"githubUrl":"https://github.com/swc-project/swc/blob/5176682b65416c6b5de6b47379ae1588ea3ecb3f/crates/swc_html_parser/src/parser/mod.rs#L1937-L1973","documentation":"The in-head insertion mode (crates/swc_html_parser/src/parser/mod.rs:1955) received a start tag named head while the head element is already the open element. The spec's message for this arm maps to SomethingSeenWhenSomethingOpen — 'start tag seen but an element of the same type was already open'. The token is ignored; the existing head continues.","triggerScenarios":"A second `` start tag while still inside head: `t`. Comments/metadata before it do not close head, so the duplicate lands in this arm.","commonSituations":"Two head partials concatenated by the layout system, boilerplate injected twice by CMS plugins, refactors that moved head content without removing the old wrapper tag.","solutions":["Merge the two head sections into one","Make the layout render exactly one wrapper around all metadata","Filter ErrorKind::SomethingSeenWhenSomethingOpen(tag) with tag == \"head\" if duplicates are benign"],"exampleFix":"\n\n\n \n \n \n t\n \n\n\n\n\n\n \n \n t\n \n","handlingStrategy":"validation","validationCode":"fn head_start_tag_count(html: &str) -> usize {\n let lower = html.to_ascii_lowercase();\n lower\n .match_indices(\"\n lower[*i + 5..].starts_with(|c: char| !(c.is_ascii_alphanumeric() || c == '-'))\n })\n .count()\n}","typeGuard":null,"tryCatchPattern":"use swc_html_parser::error::ErrorKind;\n\nlet mut errors = Vec::new();\nlet doc = swc_html_parser::parse_file_as_document(&fm, config, &mut errors)?;\n\nfor err in &errors {\n if let ErrorKind::SomethingSeenWhenSomethingOpen(tag) = err.kind() {\n if tag == \"head\" {\n // Second ignored; its attributes did NOT merge.\n log::warn!(\"duplicate start tag ignored\");\n }\n }\n}","preventionTips":["Only the page shell template may open ; partials contribute metadata, not wrappers","Guard against double-rendering head boilerplate in plugin pipelines","Note: the ignored duplicate's attributes are dropped — set lang/class on the first "],"tags":["html","parser","head","duplicate-element","insertion-mode","swc"],"backgroundTag":"duplicate-element-open","analyzedSha":"5176682b65416c6b5de6b47379ae1588ea3ecb3f","analyzedAt":"2026-08-17T16:16:52.067Z","contentChangedAt":"2026-08-17T16:16:52.067Z","schemaVersion":2},"datasetVersion":"2026-09-14T00:17:10.932Z"}