What causes "mango not found" in facebook/relay?

Dump the `sdl` string before the `.find` calls and confirm which fields are actually printed.

mango not found

Error message

mango not found

What it means

Panic from `.expect("mango not found")` in `test_object_fields_sorted_alphabetically` (compiler/crates/schema-set/src/build_schema_document.rs:963), same test as error 163. The printed SDL does not contain the `mango` field substring, so the alphabetical-ordering assertion (apple < mango < zebra) cannot proceed. The library panics because a missing field means either the printer dropped it or the input SDL no longer contains it.

Source

Thrown at compiler/crates/schema-set/src/build_schema_document.rs:963

        assert!(
            interface_pos < extension_pos,
            "Definitions should print before extensions: {}",
            sdl,
        );
    }

    #[test]
    fn test_object_fields_sorted_alphabetically() {
        let sdl = schema_sdl(indoc! {r#"
            type Foo {
              zebra: String
              apple: Int
              mango: Boolean
            }
        "#});
        // Fields should be sorted alphabetically
        let apple_pos = sdl.find("apple").expect("apple not found");
        let mango_pos = sdl.find("mango").expect("mango not found");
        let zebra_pos = sdl.find("zebra").expect("zebra not found");
        assert!(
            apple_pos < mango_pos && mango_pos < zebra_pos,
            "Fields should be sorted: {}",
            sdl,
        );
    }

    // --- Interface ---

    #[test]
    fn test_interface_with_fields() {
        let sdl = schema_sdl(indoc! {r#"
            interface Node {
              id: ID!
            }
        "#});
        assert!(sdl.contains("interface Node"), "Got: {}", sdl);

View on GitHub (pinned to 668b1b85e0)

Solutions

Dump the `sdl` string before the `.find` calls and confirm which fields are actually printed.
Verify the test SDL still declares `mango: Boolean` with exact spelling/casing.
Fix the printer in build_schema_document.rs if object fields are being omitted, then re-run `cargo test -p schema-set`.
Harden the assertions with `.unwrap_or_else(|| panic!(... sdl ...))` so output is shown on any future miss.

Example fix

// before
let mango_pos = sdl.find("mango").expect("mango not found");
// after
let mango_pos = sdl
    .find("mango")
    .unwrap_or_else(|| panic!("mango not found in SDL:\n{}", sdl));

Defensive patterns

Strategy: validation

Validate before calling

// Validate presence of every field before ordering assertions:
assert!(sdl.contains("mango"), "SDL missing 'mango'\n{}", sdl);

Type guard

fn sdl_field_position<'a>(sdl: &'a str, field: &str) -> Option<usize> {
    sdl.find(field)
}

Try / catch

let mango_pos = sdl
    .find("mango")
    .unwrap_or_else(|| panic!("mango not found; SDL:\n{}", sdl));

Prevention

Verify exact field spelling/case in the fixture SDL matches the `.find` argument.
Embed the SDL in the assertion message so drops are visible immediately.
Re-run schema-set tests after any printer ordering change since these assertions are position-sensitive.
Prefer asserting on structured printer output (if an API exists) over raw substring positions when possible.

When it happens

Trigger: Same as error 163: `to_sdl_definition()` output for `type Foo { zebra: String apple: Int mango: Boolean }` lacks `mango`. Also occurs if `mango` was renamed or the printer emits fields in a way that renames/escapes them.

Common situations: Field-dropping regression in the SDL printer; editing the test's `indoc!` SDL and forgetting to update all three lookup strings; case sensitivity issues (`Mango` vs `mango`) after a naming-convention change.

Related errors

AI-assisted analysis of facebook/relay@668b1b85e0 (2026-09-02). Data as JSON: /api/errors/96d4a38f25a7894c. Report an issue: GitHub.