oxc-project/oxc · error

Expected a `break` statement before `case`.

Error message

Expected a `break` statement before `case`.

What it means

Diagnostic from oxlint's no-fallthrough rule (ESLint port, eslint:recommended). A switch case block that reaches its end without a terminating statement (break, return, throw, continue, or an unreachable end) falls through into the next case, which is almost always a bug. The rule flags the missing break before the next case unless the case ends with a comment matching the fallthrough comment pattern ('// falls through' by default, configurable via commentPattern).

Source

Thrown at crates/oxc_linter/src/rules/eslint/no_fallthrough.rs:32

use oxc_cfg::{
    BlockNodeId, EdgeType, ErrorEdgeKind, InstructionKind,
    graph::{
        Direction,
        visit::{EdgeRef, neighbors_filtered_by_edge_weight},
    },
};
use oxc_diagnostics::OxcDiagnostic;
use oxc_macros::declare_oxc_lint;
use oxc_span::{GetSpan, Span};

use crate::{
    AstNode,
    context::LintContext,
    rule::{DefaultRuleConfig, Rule},
};

fn no_fallthrough_case_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Expected a `break` statement before `case`.")
        .with_help("Use a `break` statement to prevent fallthrough, or add a comment to indicate intentional fallthrough.")
        .with_label(span)
}

fn no_fallthrough_default_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn("Expected a `break` statement before `default`.")
        .with_help("Use a `break` statement to prevent fallthrough, or add a comment to indicate intentional fallthrough.")
        .with_label(span)
}

fn no_unused_fallthrough_diagnostic(span: Span) -> OxcDiagnostic {
    OxcDiagnostic::warn(
        "Found a comment that would permit fallthrough, but case cannot fall through.",
    )
    .with_help(
        "Remove the fallthrough comment or add code that allows fallthrough (e.g. remove `break`).",
    )
    .with_label(span)

View on GitHub (pinned to e1e7af627c)

Solutions

1. Add break; (or an early return/throw) at the end of the case block.
2. If the fallthrough is intentional, end the case with // falls through (or a comment matching your commentPattern).
3. Fix the rule's commentPattern regex in .oxlintrc.json if your team writes a different marker.

Example fix

// before
switch (code) {
  case 1:
    log('one');
  case 2:
    log('two');
    break;
}

// after
switch (code) {
  case 1:
    log('one');
    break;
  case 2:
    log('two');
    break;
}

npx oxlint -A all -D no-fallthrough src/  # fail the build on fallthrough only

When it happens

Trigger: case 1: whose last statement is a plain expression followed by case 2:; a case ending in a let/const declaration (declarations do not terminate); deliberate fallthrough without a '// falls through' comment; a custom commentPattern regex that no longer matches the team's marker spelling.

Common situations: A refactor deletes the last line of a case and the break goes with it; merging switch branches without adding a fallthrough comment; teams commenting in another language (e.g. '// cae en cascada') while the config expects the English marker.

Related errors

• Expected a `break` statement before `default`.
• Checking `switch` discriminant against NaN will never match
• Checking for NaN in `case` clause will never match
• Found a comment that would permit fallthrough, but case cann
• Unnecessary return statement.

AI-assisted analysis of oxc-project/oxc@e1e7af627c (2026-08-20). Data as JSON: /api/errors/ed9287740c5fe54e. Report an issue: GitHub.