gleam-lang/gleam · error

Type checking ensures there is at least one statement

Error message

Type checking ensures there is at least one statement

What it means

The cross-module function inliner stores inlined statement lists as Vec<TypedStatement> and converts them into the NonEmptyStatements type with try_into().expect("Type checking ensures there is at least one statement") (inline.rs:1026). Gleam function bodies always contain at least one expression after parsing/type-checking, so an empty list here means an internal invariant broke — an internal compiler error (ICE), not something caused by your project configuration.

Source

Thrown at compiler-core/src/inline.rs:1026

        self.position = Position::InlinedFunction;
        let variables = self.renamed_variables.clone();

        // Perform inlining on each of the statements in this function's body,
        // potentially inlining parameters and function calls inside this function.
        statements.extend(body.into_iter().map(|statement| self.statement(statement)));

        // Restore scope
        self.inline_variables = inline_variables;
        self.position = position;
        self.renamed_variables = variables;

        // We try to expand this block, so a function which is inlined as a
        // single expression does not get wrapped unnecessarily
        expand_block(TypedExpr::Block {
            location: BLANK_LOCATION,
            statements: statements
                .try_into()
                .expect("Type checking ensures there is at least one statement"),
        })
    }

    fn pipeline(
        &mut self,
        location: SrcSpan,
        first_value: TypedPipelineAssignment,
        assignments: Vec<(TypedPipelineAssignment, PipelineAssignmentKind)>,
        finally: Box<TypedExpr>,
        finally_kind: PipelineAssignmentKind,
    ) -> TypedExpr {
        let first_value = self.pipeline_assignment(first_value);
        let assignments = assignments
            .into_iter()
            .map(|(assignment, kind)| (self.pipeline_assignment(assignment), kind))
            .collect();
        let finally = self.boxed_expression(finally);

View on GitHub (pinned to 7e623aa83d)

Solutions

1. Delete the build cache and rebuild: `rm -rf build && gleam build` — this is the fix for the stale-cache variant.
2. Pin the compiler version that previously worked (`gleam-toolchain`/mise/asdf) until you can upgrade to a release with the fix.
3. If it reproduces on a clean build, minimize the failing module and report it with the panic backtrace at github.com/gleam-lang/gleam.
4. As a workaround, stop the function from being inlined: make it non-trivial or move it out of the cross-module inline path (e.g. avoid marking it for inlining).

Example fix

# before: stale artifacts from an older compiler
rm -rf build  # forgotten after `gleam` upgrade

# after: always clear generated code caches across toolchain changes
rm -rf build && gleam clean && gleam build

// Tooling that drives gleam_core's build in-process: isolate ICEs so a
// compiler bug is reportable instead of fatal.
let result = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
    build::main(paths, options)
}));
match result {
    Ok(Ok(())) => {}
    Ok(Err(e)) => eprintln!("gleam error: {e:?}"),
    Err(payload) => eprintln!("internal compiler error: {payload:?} — please report with backtrace"),
}

When it happens

Trigger: Compiling code whose inlinable function body round-trips through the incremental build cache with zero statements — typically a stale/corrupted build directory after a compiler upgrade, or an inliner bug on an unusual expression shape (e.g. a function body that became empty after inlining substitutions).

Common situations: Upgrading gleam versions but keeping the old `build/` directory; CI caches (actions/cache over build/) reused across toolchain updates; exotic pipelines/case expressions exercising inliner edge cases.

Related errors

• Type-checking ensured that the body has at least 1 statement
• Custom type must have at least one definition here
• `panic` expression evaluated.
• Non-UTF8 path in hardlink_dir
• Writing warning to stderr

AI-assisted analysis of gleam-lang/gleam@7e623aa83d (2026-08-17). Data as JSON: /api/errors/61687e7c05dea61b. Report an issue: GitHub.