gfx-rs/wgpu · error

Unexpected max({:?})

Error message

Unexpected max({:?})

What it means

Same family as 108 but for MathFunction::Max: the backend maps arg_scalar_kind Float/Sint/Uint to GlslStd450 FMax/SMax/UMax; any other kind (including Bool — note the WGSL spec only defines max for numeric types) triggers `unimplemented!("Unexpected max({:?})", other)` in cache_expression_value under write_block, aborting SPIR-V generation.

Source

Thrown at naga/src/back/spv/block.rs:1412

                                    result_type_id,
                                    id,
                                    arg0_id,
                                ))
                            }
                            other => unimplemented!("Unexpected abs({:?})", other),
                        }
                    }
                    Mf::Min => MathOp::Ext(match arg_scalar_kind {
                        Some(crate::ScalarKind::Float) => spirv::GlslStd450Op::FMin,
                        Some(crate::ScalarKind::Sint) => spirv::GlslStd450Op::SMin,
                        Some(crate::ScalarKind::Uint) => spirv::GlslStd450Op::UMin,
                        other => unimplemented!("Unexpected min({:?})", other),
                    }),
                    Mf::Max => MathOp::Ext(match arg_scalar_kind {
                        Some(crate::ScalarKind::Float) => spirv::GlslStd450Op::FMax,
                        Some(crate::ScalarKind::Sint) => spirv::GlslStd450Op::SMax,
                        Some(crate::ScalarKind::Uint) => spirv::GlslStd450Op::UMax,
                        other => unimplemented!("Unexpected max({:?})", other),
                    }),
                    Mf::Clamp => match arg_scalar_kind {
                        // Clamp is undefined if min > max. In practice this means it can use a median-of-three
                        // instruction to determine the value. This is fine according to the WGSL spec for float
                        // clamp, but integer clamp _must_ use min-max. As such we write out min/max.
                        Some(crate::ScalarKind::Float) => MathOp::Ext(spirv::GlslStd450Op::FClamp),
                        Some(_) => {
                            let (min_op, max_op) = match arg_scalar_kind {
                                Some(crate::ScalarKind::Sint) => {
                                    (spirv::GlslStd450Op::SMin, spirv::GlslStd450Op::SMax)
                                }
                                Some(crate::ScalarKind::Uint) => {
                                    (spirv::GlslStd450Op::UMin, spirv::GlslStd450Op::UMax)
                                }
                                _ => unreachable!(),
                            };

                            let max_id = self.gen_id();

View on GitHub (pinned to 3e11ff59bf)

Solutions

1. Restrict max() calls to numeric (f32/i32/u32, or matching vectors) arguments
2. Validate the IR module before SPIR-V emission
3. Dump IR to identify the bad max call site
4. File a naga issue with the shader if it is valid WGSL

Example fix

// before
let m = max(flag_a, flag_b); // bools
// after
let m = select(flag_b, flag_a, flag_a); // or compute on numeric values

assert!(matches!(arg_scalar_kind, Some(crate::ScalarKind::Float | crate::ScalarKind::Sint | crate::ScalarKind::Uint)), "max() requires numeric argument");

fn min_max_supported(kind: Option<crate::ScalarKind>) -> bool {
    matches!(kind, Some(crate::ScalarKind::Float | crate::ScalarKind::Sint | crate::ScalarKind::Uint))
}

When it happens

Trigger: A `max(a, b)` call whose argument scalar kind is None or otherwise unmapped (bool, composite, pointer) when the SPIR-V backend lowers math functions.

Common situations: Fuzzed/unvalidated IR with max over booleans; calling naga's spv backend directly on hand-built modules; type-inference changes after naga upgrades altering arg_scalar_kind.

Related errors

• Unexpected abs({:?})
• Unexpected min({:?})
• not implemented
• metal does not support vertex ray hit return
• not implemented

AI-assisted analysis of gfx-rs/wgpu@3e11ff59bf (2026-09-03). Data as JSON: /api/errors/c84f7894269ac00d. Report an issue: GitHub.