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Merge pull request #755 from zcash/lookup-errors 

`plonk::Error::TableError`: Better lookup errors
This commit is contained in:
Daira Hopwood 2023-04-04 23:27:28 +00:00 committed by GitHub
parent 2633567840 72ce521084
commit 5678a506cb
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GPG Key ID: 4AEE18F83AFDEB23
7 changed files with 470 additions and 144 deletions
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9
halo2_proofs/src/circuit.rs
View File

@ -13,6 +13,9 @@ pub mod floor_planner;
pub use floor_planner::single_pass::SimpleFloorPlanner;
pub mod layouter;
mod table_layouter;
pub use table_layouter::TableLayouter;
/// A chip implements a set of instructions that can be used by gadgets.
///
@ -365,11 +368,11 @@ impl<'r, F: Field> Region<'r, F> {
/// A lookup table in the circuit.
#[derive(Debug)]
pub struct Table<'r, F: Field> {
table: &'r mut dyn layouter::TableLayouter<F>,
table: &'r mut dyn TableLayouter<F>,
}
impl<'r, F: Field> From<&'r mut dyn layouter::TableLayouter<F>> for Table<'r, F> {
fn from(table: &'r mut dyn layouter::TableLayouter<F>) -> Self {
impl<'r, F: Field> From<&'r mut dyn TableLayouter<F>> for Table<'r, F> {
fn from(table: &'r mut dyn TableLayouter<F>) -> Self {
Table { table }
}
}

104
halo2_proofs/src/circuit/floor_planner/single_pass.rs
View File

@ -7,8 +7,9 @@ use ff::Field;
use crate::{
circuit::{
layouter::{RegionColumn, RegionLayouter, RegionShape, TableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, Value,
layouter::{RegionColumn, RegionLayouter, RegionShape},
table_layouter::{compute_table_lengths, SimpleTableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, TableLayouter, Value,
},
plonk::{
Advice, Any, Assigned, Assignment, Circuit, Column, Error, Fixed, FloorPlanner, Instance,
@ -165,24 +166,7 @@ impl<'a, F: Field, CS: Assignment<F> + 'a> Layouter<F> for SingleChipLayouter<'a
// Check that all table columns have the same length `first_unused`,
// and all cells up to that length are assigned.
let first_unused = {
match default_and_assigned
.values()
.map(|(_, assigned)| {
if assigned.iter().all(|b| *b) {
Some(assigned.len())
} else {
None
}
})
.reduce(|acc, item| match (acc, item) {
(Some(a), Some(b)) if a == b => Some(a),
_ => None,
}) {
Some(Some(len)) => len,
_ => return Err(Error::Synthesis), // TODO better error
}
};
let first_unused = compute_table_lengths(&default_and_assigned)?;
// Record these columns so that we can prevent them from being used again.
for column in default_and_assigned.keys() {
@ -378,86 +362,6 @@ impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> RegionLayouter<F>
}
}
/// The default value to fill a table column with.
///
/// - The outer `Option` tracks whether the value in row 0 of the table column has been
/// assigned yet. This will always be `Some` once a valid table has been completely
/// assigned.
/// - The inner `Value` tracks whether the underlying `Assignment` is evaluating
/// witnesses or not.
type DefaultTableValue<F> = Option<Value<Assigned<F>>>;
pub(crate) struct SimpleTableLayouter<'r, 'a, F: Field, CS: Assignment<F> + 'a> {
cs: &'a mut CS,
used_columns: &'r [TableColumn],
// maps from a fixed column to a pair (default value, vector saying which rows are assigned)
pub(crate) default_and_assigned: HashMap<TableColumn, (DefaultTableValue<F>, Vec<bool>)>,
}
impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> fmt::Debug for SimpleTableLayouter<'r, 'a, F, CS> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("SimpleTableLayouter")
.field("used_columns", &self.used_columns)
.field("default_and_assigned", &self.default_and_assigned)
.finish()
}
}
impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> SimpleTableLayouter<'r, 'a, F, CS> {
pub(crate) fn new(cs: &'a mut CS, used_columns: &'r [TableColumn]) -> Self {
SimpleTableLayouter {
cs,
used_columns,
default_and_assigned: HashMap::default(),
}
}
}
impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> TableLayouter<F>
for SimpleTableLayouter<'r, 'a, F, CS>
{
fn assign_cell<'v>(
&'v mut self,
annotation: &'v (dyn Fn() -> String + 'v),
column: TableColumn,
offset: usize,
to: &'v mut (dyn FnMut() -> Value<Assigned<F>> + 'v),
) -> Result<(), Error> {
if self.used_columns.contains(&column) {
return Err(Error::Synthesis); // TODO better error
}
let entry = self.default_and_assigned.entry(column).or_default();
let mut value = Value::unknown();
self.cs.assign_fixed(
annotation,
column.inner(),
offset, // tables are always assigned starting at row 0
|| {
let res = to();
value = res;
res
},
)?;
match (entry.0.is_none(), offset) {
// Use the value at offset 0 as the default value for this table column.
(true, 0) => entry.0 = Some(value),
// Since there is already an existing default value for this table column,
// the caller should not be attempting to assign another value at offset 0.
(false, 0) => return Err(Error::Synthesis), // TODO better error
_ => (),
}
if entry.1.len() <= offset {
entry.1.resize(offset + 1, false);
}
entry.1[offset] = true;
Ok(())
}
}
#[cfg(test)]
mod tests {
use pasta_curves::vesta;

25
halo2_proofs/src/circuit/floor_planner/v1.rs
View File

@ -4,9 +4,9 @@ use ff::Field;
use crate::{
circuit::{
floor_planner::single_pass::SimpleTableLayouter,
layouter::{RegionColumn, RegionLayouter, RegionShape, TableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, Value,
layouter::{RegionColumn, RegionLayouter, RegionShape},
table_layouter::{compute_table_lengths, SimpleTableLayouter},
Cell, Layouter, Region, RegionIndex, RegionStart, Table, TableLayouter, Value,
},
plonk::{
Advice, Any, Assigned, Assignment, Circuit, Column, Error, Fixed, FloorPlanner, Instance,
@ -306,24 +306,7 @@ impl<'p, 'a, F: Field, CS: Assignment<F> + 'a> AssignmentPass<'p, 'a, F, CS> {
// Check that all table columns have the same length `first_unused`,
// and all cells up to that length are assigned.
let first_unused = {
match default_and_assigned
.values()
.map(|(_, assigned)| {
if assigned.iter().all(|b| *b) {
Some(assigned.len())
} else {
None
}
})
.reduce(|acc, item| match (acc, item) {
(Some(a), Some(b)) if a == b => Some(a),
_ => None,
}) {
Some(Some(len)) => len,
_ => return Err(Error::Synthesis), // TODO better error
}
};
let first_unused = compute_table_lengths(&default_and_assigned)?;
// Record these columns so that we can prevent them from being used again.
for column in default_and_assigned.keys() {

21
halo2_proofs/src/circuit/layouter.rs
View File

@ -6,8 +6,9 @@ use std::fmt;
use ff::Field;
pub use super::table_layouter::TableLayouter;
use super::{Cell, RegionIndex, Value};
use crate::plonk::{Advice, Any, Assigned, Column, Error, Fixed, Instance, Selector, TableColumn};
use crate::plonk::{Advice, Any, Assigned, Column, Error, Fixed, Instance, Selector};
/// Helper trait for implementing a custom [`Layouter`].
///
@ -109,24 +110,6 @@ pub trait RegionLayouter<F: Field>: fmt::Debug {
fn constrain_equal(&mut self, left: Cell, right: Cell) -> Result<(), Error>;
}
/// Helper trait for implementing a custom [`Layouter`].
///
/// This trait is used for implementing table assignments.
///
/// [`Layouter`]: super::Layouter
pub trait TableLayouter<F: Field>: fmt::Debug {
/// Assigns a fixed value to a table cell.
///
/// Returns an error if the table cell has already been assigned to.
fn assign_cell<'v>(
&'v mut self,
annotation: &'v (dyn Fn() -> String + 'v),
column: TableColumn,
offset: usize,
to: &'v mut (dyn FnMut() -> Value<Assigned<F>> + 'v),
) -> Result<(), Error>;
}
/// The shape of a region. For a region at a certain index, we track
/// the set of columns it uses as well as the number of rows it uses.
#[derive(Clone, Debug)]

407
halo2_proofs/src/circuit/table_layouter.rs Normal file
View File

@ -0,0 +1,407 @@
//! Implementations of common table layouters.
use std::{
collections::HashMap,
fmt::{self, Debug},
};
use ff::Field;
use crate::plonk::{Assigned, Assignment, Error, TableColumn, TableError};
use super::Value;
/// Helper trait for implementing a custom [`Layouter`].
///
/// This trait is used for implementing table assignments.
///
/// [`Layouter`]: super::Layouter
pub trait TableLayouter<F: Field>: std::fmt::Debug {
/// Assigns a fixed value to a table cell.
///
/// Returns an error if the table cell has already been assigned to.
fn assign_cell<'v>(
&'v mut self,
annotation: &'v (dyn Fn() -> String + 'v),
column: TableColumn,
offset: usize,
to: &'v mut (dyn FnMut() -> Value<Assigned<F>> + 'v),
) -> Result<(), Error>;
}
/// The default value to fill a table column with.
///
/// - The outer `Option` tracks whether the value in row 0 of the table column has been
/// assigned yet. This will always be `Some` once a valid table has been completely
/// assigned.
/// - The inner `Value` tracks whether the underlying `Assignment` is evaluating
/// witnesses or not.
type DefaultTableValue<F> = Option<Value<Assigned<F>>>;
pub(crate) struct SimpleTableLayouter<'r, 'a, F: Field, CS: Assignment<F> + 'a> {
cs: &'a mut CS,
used_columns: &'r [TableColumn],
// maps from a fixed column to a pair (default value, vector saying which rows are assigned)
pub(crate) default_and_assigned: HashMap<TableColumn, (DefaultTableValue<F>, Vec<bool>)>,
}
impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> fmt::Debug for SimpleTableLayouter<'r, 'a, F, CS> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("SimpleTableLayouter")
.field("used_columns", &self.used_columns)
.field("default_and_assigned", &self.default_and_assigned)
.finish()
}
}
impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> SimpleTableLayouter<'r, 'a, F, CS> {
pub(crate) fn new(cs: &'a mut CS, used_columns: &'r [TableColumn]) -> Self {
SimpleTableLayouter {
cs,
used_columns,
default_and_assigned: HashMap::default(),
}
}
}
impl<'r, 'a, F: Field, CS: Assignment<F> + 'a> TableLayouter<F>
for SimpleTableLayouter<'r, 'a, F, CS>
{
fn assign_cell<'v>(
&'v mut self,
annotation: &'v (dyn Fn() -> String + 'v),
column: TableColumn,
offset: usize,
to: &'v mut (dyn FnMut() -> Value<Assigned<F>> + 'v),
) -> Result<(), Error> {
if self.used_columns.contains(&column) {
return Err(Error::TableError(TableError::UsedColumn(column)));
}
let entry = self.default_and_assigned.entry(column).or_default();
let mut value = Value::unknown();
self.cs.assign_fixed(
annotation,
column.inner(),
offset, // tables are always assigned starting at row 0
|| {
let res = to();
value = res;
res
},
)?;
match (entry.0.is_none(), offset) {
// Use the value at offset 0 as the default value for this table column.
(true, 0) => entry.0 = Some(value),
// Since there is already an existing default value for this table column,
// the caller should not be attempting to assign another value at offset 0.
(false, 0) => {
return Err(Error::TableError(TableError::OverwriteDefault(
column,
format!("{:?}", entry.0.unwrap()),
format!("{:?}", value),
)))
}
_ => (),
}
if entry.1.len() <= offset {
entry.1.resize(offset + 1, false);
}
entry.1[offset] = true;
Ok(())
}
}
pub(crate) fn compute_table_lengths<F: Debug>(
default_and_assigned: &HashMap<TableColumn, (DefaultTableValue<F>, Vec<bool>)>,
) -> Result<usize, Error> {
let column_lengths: Result<Vec<_>, Error> = default_and_assigned
.iter()
.map(|(col, (default_value, assigned))| {
if default_value.is_none() || assigned.is_empty() {
return Err(Error::TableError(TableError::ColumnNotAssigned(*col)));
}
if assigned.iter().all(|b| *b) {
// All values in the column have been assigned
Ok((col, assigned.len()))
} else {
Err(Error::TableError(TableError::ColumnNotAssigned(*col)))
}
})
.collect();
let column_lengths = column_lengths?;
column_lengths
.into_iter()
.try_fold((None, 0), |acc, (col, col_len)| {
if acc.1 == 0 || acc.1 == col_len {
Ok((Some(*col), col_len))
} else {
let mut cols = [(*col, col_len), (acc.0.unwrap(), acc.1)];
cols.sort();
Err(Error::TableError(TableError::UnevenColumnLengths(
cols[0], cols[1],
)))
}
})
.map(|col_len| col_len.1)
}
#[cfg(test)]
mod tests {
use pasta_curves::Fp;
use crate::{
circuit::{Layouter, SimpleFloorPlanner},
dev::MockProver,
plonk::{Circuit, ConstraintSystem},
poly::Rotation,
};
use super::*;
#[test]
fn table_no_default() {
const K: u32 = 4;
#[derive(Clone)]
struct FaultyCircuitConfig {
table: TableColumn,
}
struct FaultyCircuit;
impl Circuit<Fp> for FaultyCircuit {
type Config = FaultyCircuitConfig;
type FloorPlanner = SimpleFloorPlanner;
fn without_witnesses(&self) -> Self {
Self
}
fn configure(meta: &mut ConstraintSystem<Fp>) -> Self::Config {
let a = meta.advice_column();
let table = meta.lookup_table_column();
meta.lookup(|cells| {
let a = cells.query_advice(a, Rotation::cur());
vec![(a, table)]
});
Self::Config { table }
}
fn synthesize(
&self,
config: Self::Config,
mut layouter: impl Layouter<Fp>,
) -> Result<(), Error> {
layouter.assign_table(
|| "duplicate assignment",
|mut table| {
table.assign_cell(
|| "default",
config.table,
1,
|| Value::known(Fp::zero()),
)
},
)
}
}
let prover = MockProver::run(K, &FaultyCircuit, vec![]);
assert_eq!(
format!("{}", prover.unwrap_err()),
"TableColumn { inner: Column { index: 0, column_type: Fixed } } not fully assigned. Help: assign a value at offset 0."
);
}
#[test]
fn table_overwrite_default() {
const K: u32 = 4;
#[derive(Clone)]
struct FaultyCircuitConfig {
table: TableColumn,
}
struct FaultyCircuit;
impl Circuit<Fp> for FaultyCircuit {
type Config = FaultyCircuitConfig;
type FloorPlanner = SimpleFloorPlanner;
fn without_witnesses(&self) -> Self {
Self
}
fn configure(meta: &mut ConstraintSystem<Fp>) -> Self::Config {
let a = meta.advice_column();
let table = meta.lookup_table_column();
meta.lookup(|cells| {
let a = cells.query_advice(a, Rotation::cur());
vec![(a, table)]
});
Self::Config { table }
}
fn synthesize(
&self,
config: Self::Config,
mut layouter: impl Layouter<Fp>,
) -> Result<(), Error> {
layouter.assign_table(
|| "duplicate assignment",
|mut table| {
table.assign_cell(
|| "default",
config.table,
0,
|| Value::known(Fp::zero()),
)?;
table.assign_cell(
|| "duplicate",
config.table,
0,
|| Value::known(Fp::zero()),
)
},
)
}
}
let prover = MockProver::run(K, &FaultyCircuit, vec![]);
assert_eq!(
format!("{}", prover.unwrap_err()),
"Attempted to overwrite default value Value { inner: Some(Trivial(0x0000000000000000000000000000000000000000000000000000000000000000)) } with Value { inner: Some(Trivial(0x0000000000000000000000000000000000000000000000000000000000000000)) } in TableColumn { inner: Column { index: 0, column_type: Fixed } }"
);
}
#[test]
fn table_reuse_column() {
const K: u32 = 4;
#[derive(Clone)]
struct FaultyCircuitConfig {
table: TableColumn,
}
struct FaultyCircuit;
impl Circuit<Fp> for FaultyCircuit {
type Config = FaultyCircuitConfig;
type FloorPlanner = SimpleFloorPlanner;
fn without_witnesses(&self) -> Self {
Self
}
fn configure(meta: &mut ConstraintSystem<Fp>) -> Self::Config {
let a = meta.advice_column();
let table = meta.lookup_table_column();
meta.lookup(|cells| {
let a = cells.query_advice(a, Rotation::cur());
vec![(a, table)]
});
Self::Config { table }
}
fn synthesize(
&self,
config: Self::Config,
mut layouter: impl Layouter<Fp>,
) -> Result<(), Error> {
layouter.assign_table(
|| "first assignment",
|mut table| {
table.assign_cell(
|| "default",
config.table,
0,
|| Value::known(Fp::zero()),
)
},
)?;
layouter.assign_table(
|| "reuse",
|mut table| {
table.assign_cell(|| "reuse", config.table, 1, || Value::known(Fp::zero()))
},
)
}
}
let prover = MockProver::run(K, &FaultyCircuit, vec![]);
assert_eq!(
format!("{}", prover.unwrap_err()),
"TableColumn { inner: Column { index: 0, column_type: Fixed } } has already been used"
);
}
#[test]
fn table_uneven_columns() {
const K: u32 = 4;
#[derive(Clone)]
struct FaultyCircuitConfig {
table: (TableColumn, TableColumn),
}
struct FaultyCircuit;
impl Circuit<Fp> for FaultyCircuit {
type Config = FaultyCircuitConfig;
type FloorPlanner = SimpleFloorPlanner;
fn without_witnesses(&self) -> Self {
Self
}
fn configure(meta: &mut ConstraintSystem<Fp>) -> Self::Config {
let a = meta.advice_column();
let table = (meta.lookup_table_column(), meta.lookup_table_column());
meta.lookup(|cells| {
let a = cells.query_advice(a, Rotation::cur());
vec![(a.clone(), table.0), (a, table.1)]
});
Self::Config { table }
}
fn synthesize(
&self,
config: Self::Config,
mut layouter: impl Layouter<Fp>,
) -> Result<(), Error> {
layouter.assign_table(
|| "table with uneven columns",
|mut table| {
table.assign_cell(|| "", config.table.0, 0, || Value::known(Fp::zero()))?;
table.assign_cell(|| "", config.table.0, 1, || Value::known(Fp::zero()))?;
table.assign_cell(|| "", config.table.1, 0, || Value::known(Fp::zero()))
},
)
}
}
let prover = MockProver::run(K, &FaultyCircuit, vec![]);
assert_eq!(
format!("{}", prover.unwrap_err()),
"TableColumn { inner: Column { index: 0, column_type: Fixed } } has length 2 while TableColumn { inner: Column { index: 1, column_type: Fixed } } has length 1"
);
}
}

2
halo2_proofs/src/plonk/circuit.rs
View File

@ -311,7 +311,7 @@ pub struct InstanceQuery {
/// they cannot simultaneously be used as general fixed columns.
///
/// [`Layouter::assign_table`]: crate::circuit::Layouter::assign_table
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash)]
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub struct TableColumn {
/// The fixed column that this table column is stored in.
///

46
halo2_proofs/src/plonk/error.rs
View File

@ -2,6 +2,7 @@ use std::error;
use std::fmt;
use std::io;
use super::TableColumn;
use super::{Any, Column};
/// This is an error that could occur during proving or circuit synthesis.
@ -37,6 +38,8 @@ pub enum Error {
/// The instance sets up a copy constraint involving a column that has not been
/// included in the permutation.
ColumnNotInPermutation(Column<Any>),
/// An error relating to a lookup table.
TableError(TableError),
}
impl From<io::Error> for Error {
@ -79,6 +82,7 @@ impl fmt::Display for Error {
"Column {:?} must be included in the permutation. Help: try applying `meta.enable_equalty` on the column",
column
),
Error::TableError(error) => write!(f, "{}", error)
}
}
}
@ -91,3 +95,45 @@ impl error::Error for Error {
}
}
}
/// This is an error that could occur during table synthesis.
#[derive(Debug)]
pub enum TableError {
/// A `TableColumn` has not been assigned.
ColumnNotAssigned(TableColumn),
/// A Table has columns of uneven lengths.
UnevenColumnLengths((TableColumn, usize), (TableColumn, usize)),
/// Attempt to assign a used `TableColumn`
UsedColumn(TableColumn),
/// Attempt to overwrite a default value
OverwriteDefault(TableColumn, String, String),
}
impl fmt::Display for TableError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
TableError::ColumnNotAssigned(col) => {
write!(
f,
"{:?} not fully assigned. Help: assign a value at offset 0.",
col
)
}
TableError::UnevenColumnLengths((col, col_len), (table, table_len)) => write!(
f,
"{:?} has length {} while {:?} has length {}",
col, col_len, table, table_len
),
TableError::UsedColumn(col) => {
write!(f, "{:?} has already been used", col)
}
TableError::OverwriteDefault(col, default, val) => {
write!(
f,
"Attempted to overwrite default value {} with {} in {:?}",
default, val, col
)
}
}
}
}