Merge pull request #2604 from rtfeldman/early-exhaustiveness-checking

Move out exhaustiveness checking to its own crate

Cargo.lock

@@ -3502,6 +3502,16 @@ dependencies = [
 name = "roc_error_macros"
 version = "0.1.0"
 
+[[package]]
+name = "roc_exhaustive"
+version = "0.1.0"
+dependencies = [
+ "roc_collections",
+ "roc_module",
+ "roc_region",
+ "roc_std",
+]
+
 [[package]]
 name = "roc_fmt"
 version = "0.1.0"
@@ -3651,6 +3661,7 @@ dependencies = [
  "roc_can",
  "roc_collections",
  "roc_error_macros",
+ "roc_exhaustive",
  "roc_module",
  "roc_problem",
  "roc_region",
@@ -3772,6 +3783,7 @@ dependencies = [
  "roc_can",
  "roc_collections",
  "roc_constrain",
+ "roc_exhaustive",
  "roc_module",
  "roc_mono",
  "roc_parse",

Cargo.toml

@@ -3,6 +3,7 @@ members = [
     "compiler/ident",
     "compiler/region",
     "compiler/collections",
+    "compiler/exhaustive",
     "compiler/module",
     "compiler/parse",
     "compiler/can",

compiler/exhaustive/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "roc_exhaustive"
+version = "0.1.0"
+authors = ["The Roc Contributors"]
+license = "UPL-1.0"
+edition = "2018"
+
+[dependencies]
+roc_collections = { path = "../collections" }
+roc_region = { path = "../region" }
+roc_module = { path = "../module" }
+roc_std = { path = "../../roc_std", default-features = false }

compiler/exhaustive/src/lib.rs

@@ -0,0 +1,440 @@
+use roc_collections::all::{Index, MutMap};
+use roc_module::ident::{Lowercase, TagIdIntType, TagName};
+use roc_region::all::Region;
+use roc_std::RocDec;
+
+use self::Pattern::*;
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct Union {
+    pub alternatives: Vec<Ctor>,
+    pub render_as: RenderAs,
+}
+
+impl Union {
+    pub fn newtype_wrapper(tag_name: TagName, arity: usize) -> Self {
+        let alternatives = vec![Ctor {
+            name: tag_name,
+            tag_id: TagId(0),
+            arity,
+        }];
+
+        Union {
+            alternatives,
+            render_as: RenderAs::Tag,
+        }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub enum RenderAs {
+    Tag,
+    Opaque,
+    Record(Vec<Lowercase>),
+    Guard,
+}
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash, Copy)]
+pub struct TagId(pub TagIdIntType);
+
+#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+pub struct Ctor {
+    pub name: TagName,
+    pub tag_id: TagId,
+    pub arity: usize,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Pattern {
+    Anything,
+    Literal(Literal),
+    Ctor(Union, TagId, std::vec::Vec<Pattern>),
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Literal {
+    Int(i128),
+    U128(u128),
+    Bit(bool),
+    Byte(u8),
+    Float(u64),
+    Decimal(RocDec),
+    Str(Box<str>),
+}
+
+/// Error
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Error {
+    Incomplete(Region, Context, Vec<Pattern>),
+    Redundant {
+        overall_region: Region,
+        branch_region: Region,
+        index: Index,
+    },
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Context {
+    BadArg,
+    BadDestruct,
+    BadCase,
+}
+
+#[derive(Clone, Debug, PartialEq)]
+pub enum Guard {
+    HasGuard,
+    NoGuard,
+}
+
+/// Check
+
+pub fn check(
+    region: Region,
+    context: Context,
+    matrix: Vec<Vec<Pattern>>,
+) -> Result<(), Vec<Error>> {
+    let mut errors = Vec::new();
+    let bad_patterns = is_exhaustive(&matrix, 1);
+    if !bad_patterns.is_empty() {
+        // TODO i suspect this is like a concat in in practice? code below can panic
+        // if this debug_assert! ever fails, the theory is disproven
+        debug_assert!(bad_patterns.iter().map(|v| v.len()).sum::<usize>() == bad_patterns.len());
+        let heads = bad_patterns.into_iter().map(|mut v| v.remove(0)).collect();
+        errors.push(Error::Incomplete(region, context, heads));
+        return Err(errors);
+    }
+    Ok(())
+}
+
+/// EXHAUSTIVE PATTERNS
+
+/// INVARIANTS:
+///
+///   The initial rows "matrix" are all of length 1
+///   The initial count of items per row "n" is also 1
+///   The resulting rows are examples of missing patterns
+fn is_exhaustive(matrix: &RefPatternMatrix, n: usize) -> PatternMatrix {
+    if matrix.is_empty() {
+        vec![std::iter::repeat(Anything).take(n).collect()]
+    } else if n == 0 {
+        vec![]
+    } else {
+        let ctors = collect_ctors(matrix);
+        let num_seen = ctors.len();
+
+        if num_seen == 0 {
+            let new_matrix: Vec<_> = matrix
+                .iter()
+                .filter_map(|row| specialize_row_by_anything(row))
+                .collect();
+            let mut rest = is_exhaustive(&new_matrix, n - 1);
+
+            for row in rest.iter_mut() {
+                row.push(Anything);
+            }
+
+            rest
+        } else {
+            let alts = ctors.iter().next().unwrap().1;
+
+            let alt_list = &alts.alternatives;
+            let num_alts = alt_list.len();
+
+            if num_seen < num_alts {
+                let new_matrix: Vec<_> = matrix
+                    .iter()
+                    .filter_map(|row| specialize_row_by_anything(row))
+                    .collect();
+                let rest: Vec<Vec<Pattern>> = is_exhaustive(&new_matrix, n - 1);
+
+                let last: _ = alt_list
+                    .iter()
+                    .filter_map(|r| is_missing(alts.clone(), &ctors, r));
+
+                let mut result = Vec::new();
+
+                for last_option in last {
+                    for mut row in rest.clone() {
+                        row.push(last_option.clone());
+
+                        result.push(row);
+                    }
+                }
+
+                result
+            } else {
+                let is_alt_exhaustive = |Ctor { arity, tag_id, .. }| {
+                    let new_matrix: Vec<_> = matrix
+                        .iter()
+                        .filter_map(|r| specialize_row_by_ctor(tag_id, arity, r))
+                        .collect();
+                    let rest: Vec<Vec<Pattern>> = is_exhaustive(&new_matrix, arity + n - 1);
+
+                    let mut result = Vec::with_capacity(rest.len());
+                    for row in rest {
+                        result.push(recover_ctor(alts.clone(), tag_id, arity, row));
+                    }
+
+                    result
+                };
+
+                alt_list
+                    .iter()
+                    .cloned()
+                    .map(is_alt_exhaustive)
+                    .flatten()
+                    .collect()
+            }
+        }
+    }
+}
+
+fn is_missing<T>(union: Union, ctors: &MutMap<TagId, T>, ctor: &Ctor) -> Option<Pattern> {
+    let Ctor { arity, tag_id, .. } = ctor;
+
+    if ctors.contains_key(tag_id) {
+        None
+    } else {
+        let anythings = std::iter::repeat(Anything).take(*arity).collect();
+        Some(Pattern::Ctor(union, *tag_id, anythings))
+    }
+}
+
+fn recover_ctor(
+    union: Union,
+    tag_id: TagId,
+    arity: usize,
+    mut patterns: Vec<Pattern>,
+) -> Vec<Pattern> {
+    let mut rest = patterns.split_off(arity);
+    let args = patterns;
+
+    rest.push(Ctor(union, tag_id, args));
+
+    rest
+}
+
+/// Check if a new row "vector" is useful given previous rows "matrix"
+pub fn is_useful(mut old_matrix: PatternMatrix, mut vector: Row) -> bool {
+    let mut matrix = Vec::with_capacity(old_matrix.len());
+
+    // this loop ping-pongs the rows between old_matrix and matrix
+    'outer: loop {
+        match vector.pop() {
+            _ if old_matrix.is_empty() => {
+                // No rows are the same as the new vector! The vector is useful!
+                break true;
+            }
+            None => {
+                // There is nothing left in the new vector, but we still have
+                // rows that match the same things. This is not a useful vector!
+                break false;
+            }
+            Some(first_pattern) => {
+                // NOTE: if there are bugs in this code, look at the ordering of the row/matrix
+
+                match first_pattern {
+                    // keep checking rows that start with this Ctor or Anything
+                    Ctor(_, id, args) => {
+                        specialize_row_by_ctor2(id, args.len(), &mut old_matrix, &mut matrix);
+
+                        std::mem::swap(&mut old_matrix, &mut matrix);
+
+                        vector.extend(args);
+                    }
+
+                    Anything => {
+                        // check if all alternatives appear in matrix
+                        match is_complete(&old_matrix) {
+                            Complete::No => {
+                                // This Anything is useful because some Ctors are missing.
+                                // But what if a previous row has an Anything?
+                                // If so, this one is not useful.
+                                for mut row in old_matrix.drain(..) {
+                                    if let Some(Anything) = row.pop() {
+                                        matrix.push(row);
+                                    }
+                                }
+
+                                std::mem::swap(&mut old_matrix, &mut matrix);
+                            }
+                            Complete::Yes(alternatives) => {
+                                // All Ctors are covered, so this Anything is not needed for any
+                                // of those. But what if some of those Ctors have subpatterns
+                                // that make them less general? If so, this actually is useful!
+                                for alternative in alternatives {
+                                    let Ctor { arity, tag_id, .. } = alternative;
+
+                                    let mut old_matrix = old_matrix.clone();
+                                    let mut matrix = vec![];
+                                    specialize_row_by_ctor2(
+                                        tag_id,
+                                        arity,
+                                        &mut old_matrix,
+                                        &mut matrix,
+                                    );
+
+                                    let mut vector = vector.clone();
+                                    vector.extend(std::iter::repeat(Anything).take(arity));
+
+                                    if is_useful(matrix, vector) {
+                                        break 'outer true;
+                                    }
+                                }
+
+                                break false;
+                            }
+                        }
+                    }
+
+                    Literal(literal) => {
+                        // keep checking rows that start with this Literal or Anything
+
+                        for mut row in old_matrix.drain(..) {
+                            let head = row.pop();
+                            let patterns = row;
+
+                            match head {
+                                Some(Literal(lit)) => {
+                                    if lit == literal {
+                                        matrix.push(patterns);
+                                    } else {
+                                        // do nothing
+                                    }
+                                }
+                                Some(Anything) => matrix.push(patterns),
+
+                                Some(Ctor(_, _, _)) => panic!(
+                                    r#"Compiler bug! After type checking, constructors and literals should never align in pattern match exhaustiveness checks."#
+                                ),
+
+                                None => panic!(
+                                    "Compiler error! Empty matrices should not get specialized."
+                                ),
+                            }
+                        }
+                        std::mem::swap(&mut old_matrix, &mut matrix);
+                    }
+                }
+            }
+        }
+    }
+}
+
+/// INVARIANT: (length row == N) ==> (length result == arity + N - 1)
+fn specialize_row_by_ctor2(
+    tag_id: TagId,
+    arity: usize,
+    old_matrix: &mut PatternMatrix,
+    matrix: &mut PatternMatrix,
+) {
+    for mut row in old_matrix.drain(..) {
+        let head = row.pop();
+        let mut patterns = row;
+
+        match head {
+        Some(Ctor(_, id, args)) =>
+            if id == tag_id {
+                patterns.extend(args);
+                matrix.push(patterns);
+            } else {
+                // do nothing
+            }
+        Some(Anything) => {
+            // TODO order!
+            patterns.extend(std::iter::repeat(Anything).take(arity));
+            matrix.push(patterns);
+            }
+        Some(Literal(_)) => panic!( "Compiler bug! After type checking, constructors and literal should never align in pattern match exhaustiveness checks."),
+        None => panic!("Compiler error! Empty matrices should not get specialized."),
+    }
+    }
+}
+
+/// INVARIANT: (length row == N) ==> (length result == arity + N - 1)
+fn specialize_row_by_ctor(tag_id: TagId, arity: usize, row: &RefRow) -> Option<Row> {
+    let mut row = row.to_vec();
+
+    let head = row.pop();
+    let patterns = row;
+
+    match head {
+        Some(Ctor(_, id, args)) => {
+            if id == tag_id {
+                // TODO order!
+                let mut new_patterns = Vec::new();
+                new_patterns.extend(args);
+                new_patterns.extend(patterns);
+                Some(new_patterns)
+            } else {
+                None
+            }
+        }
+        Some(Anything) => {
+            // TODO order!
+            let new_patterns = std::iter::repeat(Anything)
+                .take(arity)
+                .chain(patterns)
+                .collect();
+            Some(new_patterns)
+        }
+        Some(Literal(_)) => unreachable!(
+            r#"Compiler bug! After type checking, a constructor can never align with a literal: that should be a type error!"#
+        ),
+        None => panic!("Compiler error! Empty matrices should not get specialized."),
+    }
+}
+
+/// INVARIANT: (length row == N) ==> (length result == N-1)
+fn specialize_row_by_anything(row: &RefRow) -> Option<Row> {
+    let mut row = row.to_vec();
+
+    match row.pop() {
+        Some(Anything) => Some(row),
+        _ => None,
+    }
+}
+
+/// ALL CONSTRUCTORS ARE PRESENT?
+
+pub enum Complete {
+    Yes(Vec<Ctor>),
+    No,
+}
+
+fn is_complete(matrix: &RefPatternMatrix) -> Complete {
+    let ctors = collect_ctors(matrix);
+    let length = ctors.len();
+    let mut it = ctors.into_iter();
+
+    match it.next() {
+        None => Complete::No,
+        Some((_, Union { alternatives, .. })) => {
+            if length == alternatives.len() {
+                Complete::Yes(alternatives)
+            } else {
+                Complete::No
+            }
+        }
+    }
+}
+
+/// COLLECT CTORS
+
+type RefPatternMatrix = [Vec<Pattern>];
+type PatternMatrix = Vec<Vec<Pattern>>;
+type RefRow = [Pattern];
+type Row = Vec<Pattern>;
+
+fn collect_ctors(matrix: &RefPatternMatrix) -> MutMap<TagId, Union> {
+    let mut ctors = MutMap::default();
+
+    for row in matrix {
+        if let Some(Ctor(union, id, _)) = row.get(row.len() - 1) {
+            ctors.insert(*id, union.clone());
+        }
+    }
+
+    ctors
+}

compiler/module/src/ident.rs

@@ -40,6 +40,8 @@ pub struct Uppercase(IdentStr);
 #[derive(Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
 pub struct ForeignSymbol(IdentStr);
 
+pub type TagIdIntType = u16;
+
 #[derive(Clone, Debug, PartialEq, Eq, Hash, PartialOrd, Ord)]
 pub enum TagName {
     /// Global tags have no module, but tend to be short strings (since they're

compiler/mono/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2018"
 
 [dependencies]
 roc_collections = { path = "../collections" }
+roc_exhaustive = { path = "../exhaustive" }
 roc_region = { path = "../region" }
 roc_module = { path = "../module" }
 roc_types = { path = "../types" }

compiler/mono/src/decision_tree.rs

@@ -1,10 +1,10 @@
-use crate::exhaustive::{Ctor, RenderAs, TagId, Union};
 use crate::ir::{
     BranchInfo, DestructType, Env, Expr, JoinPointId, Literal, Param, Pattern, Procs, Stmt,
 };
 use crate::layout::{Builtin, Layout, LayoutCache, TagIdIntType, UnionLayout};
 use roc_builtins::bitcode::{FloatWidth, IntWidth};
 use roc_collections::all::{MutMap, MutSet};
+use roc_exhaustive::{Ctor, RenderAs, TagId, Union};
 use roc_module::ident::TagName;
 use roc_module::low_level::LowLevel;
 use roc_module::symbol::Symbol;
@@ -83,7 +83,7 @@ enum Test<'a> {
     IsCtor {
         tag_id: TagIdIntType,
         tag_name: TagName,
-        union: crate::exhaustive::Union,
+        union: roc_exhaustive::Union,
         arguments: Vec<(Pattern<'a>, Layout<'a>)>,
     },
     IsInt(i128, IntWidth),

compiler/mono/src/exhaustive.rs

@@ -1,67 +1,12 @@
-use crate::{ir::DestructType, layout::TagIdIntType};
-use roc_collections::all::{Index, MutMap};
-use roc_module::ident::{Lowercase, TagName};
+use crate::ir::DestructType;
+use roc_collections::all::Index;
+use roc_exhaustive::{
+    is_useful, Context, Ctor, Error, Guard, Literal, Pattern, RenderAs, TagId, Union,
+};
+use roc_module::ident::{TagIdIntType, TagName};
 use roc_region::all::{Loc, Region};
-use roc_std::RocDec;
 
-use self::Pattern::*;
-
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
-pub struct Union {
-    pub alternatives: Vec<Ctor>,
-    pub render_as: RenderAs,
-}
-
-impl Union {
-    pub fn newtype_wrapper(tag_name: TagName, arity: usize) -> Self {
-        let alternatives = vec![Ctor {
-            name: tag_name,
-            tag_id: TagId(0),
-            arity,
-        }];
-
-        Union {
-            alternatives,
-            render_as: RenderAs::Tag,
-        }
-    }
-}
-
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
-pub enum RenderAs {
-    Tag,
-    Opaque,
-    Record(Vec<Lowercase>),
-    Guard,
-}
-
-#[derive(Clone, Debug, PartialEq, Eq, Hash, Copy)]
-pub struct TagId(pub TagIdIntType);
-
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
-pub struct Ctor {
-    pub name: TagName,
-    pub tag_id: TagId,
-    pub arity: usize,
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum Pattern {
-    Anything,
-    Literal(Literal),
-    Ctor(Union, TagId, std::vec::Vec<Pattern>),
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum Literal {
-    Int(i128),
-    U128(u128),
-    Bit(bool),
-    Byte(u8),
-    Float(u64),
-    Decimal(RocDec),
-    Str(Box<str>),
-}
+use Pattern::*;
 
 fn simplify(pattern: &crate::ir::Pattern) -> Pattern {
     use crate::ir::Pattern::*;
@@ -153,33 +98,6 @@ fn simplify(pattern: &crate::ir::Pattern) -> Pattern {
     }
 }
 
-/// Error
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum Error {
-    Incomplete(Region, Context, Vec<Pattern>),
-    Redundant {
-        overall_region: Region,
-        branch_region: Region,
-        index: Index,
-    },
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum Context {
-    BadArg,
-    BadDestruct,
-    BadCase,
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub enum Guard {
-    HasGuard,
-    NoGuard,
-}
-
-/// Check
-
 pub fn check(
     region: Region,
     patterns: &[(Loc<crate::ir::Pattern>, Guard)],
@@ -204,128 +122,13 @@ pub fn check_patterns<'a>(
     match to_nonredundant_rows(region, patterns) {
         Err(err) => errors.push(err),
         Ok(matrix) => {
-            let bad_patterns = is_exhaustive(&matrix, 1);
-            if !bad_patterns.is_empty() {
-                // TODO i suspect this is like a concat in in practice? code below can panic
-                // if this debug_assert! ever fails, the theory is disproven
-                debug_assert!(
-                    bad_patterns.iter().map(|v| v.len()).sum::<usize>() == bad_patterns.len()
-                );
-                let heads = bad_patterns.into_iter().map(|mut v| v.remove(0)).collect();
-                errors.push(Error::Incomplete(region, context, heads));
+            if let Err(err) = roc_exhaustive::check(region, context, matrix) {
+                *errors = err;
             }
         }
     }
 }
 
-/// EXHAUSTIVE PATTERNS
-
-/// INVARIANTS:
-///
-///   The initial rows "matrix" are all of length 1
-///   The initial count of items per row "n" is also 1
-///   The resulting rows are examples of missing patterns
-fn is_exhaustive(matrix: &PatternMatrix, n: usize) -> PatternMatrix {
-    if matrix.is_empty() {
-        vec![std::iter::repeat(Anything).take(n).collect()]
-    } else if n == 0 {
-        vec![]
-    } else {
-        let ctors = collect_ctors(matrix);
-        let num_seen = ctors.len();
-
-        if num_seen == 0 {
-            let new_matrix = matrix
-                .iter()
-                .filter_map(specialize_row_by_anything)
-                .collect();
-            let mut rest = is_exhaustive(&new_matrix, n - 1);
-
-            for row in rest.iter_mut() {
-                row.push(Anything);
-            }
-
-            rest
-        } else {
-            let alts = ctors.iter().next().unwrap().1;
-
-            let alt_list = &alts.alternatives;
-            let num_alts = alt_list.len();
-
-            if num_seen < num_alts {
-                let new_matrix = matrix
-                    .iter()
-                    .filter_map(specialize_row_by_anything)
-                    .collect();
-                let rest: Vec<Vec<Pattern>> = is_exhaustive(&new_matrix, n - 1);
-
-                let last: _ = alt_list
-                    .iter()
-                    .filter_map(|r| is_missing(alts.clone(), &ctors, r));
-
-                let mut result = Vec::new();
-
-                for last_option in last {
-                    for mut row in rest.clone() {
-                        row.push(last_option.clone());
-
-                        result.push(row);
-                    }
-                }
-
-                result
-            } else {
-                let is_alt_exhaustive = |Ctor { arity, tag_id, .. }| {
-                    let new_matrix = matrix
-                        .iter()
-                        .filter_map(|r| specialize_row_by_ctor(tag_id, arity, r))
-                        .collect();
-                    let rest: Vec<Vec<Pattern>> = is_exhaustive(&new_matrix, arity + n - 1);
-
-                    let mut result = Vec::with_capacity(rest.len());
-                    for row in rest {
-                        result.push(recover_ctor(alts.clone(), tag_id, arity, row));
-                    }
-
-                    result
-                };
-
-                alt_list
-                    .iter()
-                    .cloned()
-                    .map(is_alt_exhaustive)
-                    .flatten()
-                    .collect()
-            }
-        }
-    }
-}
-
-fn is_missing<T>(union: Union, ctors: &MutMap<TagId, T>, ctor: &Ctor) -> Option<Pattern> {
-    let Ctor { arity, tag_id, .. } = ctor;
-
-    if ctors.contains_key(tag_id) {
-        None
-    } else {
-        let anythings = std::iter::repeat(Anything).take(*arity).collect();
-        Some(Pattern::Ctor(union, *tag_id, anythings))
-    }
-}
-
-fn recover_ctor(
-    union: Union,
-    tag_id: TagId,
-    arity: usize,
-    mut patterns: Vec<Pattern>,
-) -> Vec<Pattern> {
-    let mut rest = patterns.split_off(arity);
-    let args = patterns;
-
-    rest.push(Ctor(union, tag_id, args));
-
-    rest
-}
-
 /// REDUNDANT PATTERNS
 
 /// INVARIANT: Produces a list of rows where (forall row. length row == 1)
@@ -393,226 +196,3 @@ fn to_nonredundant_rows(
 
     Ok(checked_rows)
 }
-
-/// Check if a new row "vector" is useful given previous rows "matrix"
-fn is_useful(mut old_matrix: PatternMatrix, mut vector: Row) -> bool {
-    let mut matrix = Vec::with_capacity(old_matrix.len());
-
-    // this loop ping-pongs the rows between old_matrix and matrix
-    'outer: loop {
-        match vector.pop() {
-            _ if old_matrix.is_empty() => {
-                // No rows are the same as the new vector! The vector is useful!
-                break true;
-            }
-            None => {
-                // There is nothing left in the new vector, but we still have
-                // rows that match the same things. This is not a useful vector!
-                break false;
-            }
-            Some(first_pattern) => {
-                // NOTE: if there are bugs in this code, look at the ordering of the row/matrix
-
-                match first_pattern {
-                    // keep checking rows that start with this Ctor or Anything
-                    Ctor(_, id, args) => {
-                        specialize_row_by_ctor2(id, args.len(), &mut old_matrix, &mut matrix);
-
-                        std::mem::swap(&mut old_matrix, &mut matrix);
-
-                        vector.extend(args);
-                    }
-
-                    Anything => {
-                        // check if all alternatives appear in matrix
-                        match is_complete(&old_matrix) {
-                            Complete::No => {
-                                // This Anything is useful because some Ctors are missing.
-                                // But what if a previous row has an Anything?
-                                // If so, this one is not useful.
-                                for mut row in old_matrix.drain(..) {
-                                    if let Some(Anything) = row.pop() {
-                                        matrix.push(row);
-                                    }
-                                }
-
-                                std::mem::swap(&mut old_matrix, &mut matrix);
-                            }
-                            Complete::Yes(alternatives) => {
-                                // All Ctors are covered, so this Anything is not needed for any
-                                // of those. But what if some of those Ctors have subpatterns
-                                // that make them less general? If so, this actually is useful!
-                                for alternative in alternatives {
-                                    let Ctor { arity, tag_id, .. } = alternative;
-
-                                    let mut old_matrix = old_matrix.clone();
-                                    let mut matrix = vec![];
-                                    specialize_row_by_ctor2(
-                                        tag_id,
-                                        arity,
-                                        &mut old_matrix,
-                                        &mut matrix,
-                                    );
-
-                                    let mut vector = vector.clone();
-                                    vector.extend(std::iter::repeat(Anything).take(arity));
-
-                                    if is_useful(matrix, vector) {
-                                        break 'outer true;
-                                    }
-                                }
-
-                                break false;
-                            }
-                        }
-                    }
-
-                    Literal(literal) => {
-                        // keep checking rows that start with this Literal or Anything
-
-                        for mut row in old_matrix.drain(..) {
-                            let head = row.pop();
-                            let patterns = row;
-
-                            match head {
-                                Some(Literal(lit)) => {
-                                    if lit == literal {
-                                        matrix.push(patterns);
-                                    } else {
-                                        // do nothing
-                                    }
-                                }
-                                Some(Anything) => matrix.push(patterns),
-
-                                Some(Ctor(_, _, _)) => panic!(
-                                    r#"Compiler bug! After type checking, constructors and literals should never align in pattern match exhaustiveness checks."#
-                                ),
-
-                                None => panic!(
-                                    "Compiler error! Empty matrices should not get specialized."
-                                ),
-                            }
-                        }
-                        std::mem::swap(&mut old_matrix, &mut matrix);
-                    }
-                }
-            }
-        }
-    }
-}
-
-/// INVARIANT: (length row == N) ==> (length result == arity + N - 1)
-fn specialize_row_by_ctor2(
-    tag_id: TagId,
-    arity: usize,
-    old_matrix: &mut PatternMatrix,
-    matrix: &mut PatternMatrix,
-) {
-    for mut row in old_matrix.drain(..) {
-        let head = row.pop();
-        let mut patterns = row;
-
-        match head {
-        Some(Ctor(_, id, args)) =>
-            if id == tag_id {
-                patterns.extend(args);
-                matrix.push(patterns);
-            } else {
-                // do nothing
-            }
-        Some(Anything) => {
-            // TODO order!
-            patterns.extend(std::iter::repeat(Anything).take(arity));
-            matrix.push(patterns);
-            }
-        Some(Literal(_)) => panic!( "Compiler bug! After type checking, constructors and literal should never align in pattern match exhaustiveness checks."),
-        None => panic!("Compiler error! Empty matrices should not get specialized."),
-    }
-    }
-}
-
-/// INVARIANT: (length row == N) ==> (length result == arity + N - 1)
-fn specialize_row_by_ctor(tag_id: TagId, arity: usize, row: &Row) -> Option<Row> {
-    let mut row = row.clone();
-
-    let head = row.pop();
-    let patterns = row;
-
-    match head {
-        Some(Ctor(_, id, args)) => {
-            if id == tag_id {
-                // TODO order!
-                let mut new_patterns = Vec::new();
-                new_patterns.extend(args);
-                new_patterns.extend(patterns);
-                Some(new_patterns)
-            } else {
-                None
-            }
-        }
-        Some(Anything) => {
-            // TODO order!
-            let new_patterns = std::iter::repeat(Anything)
-                .take(arity)
-                .chain(patterns)
-                .collect();
-            Some(new_patterns)
-        }
-        Some(Literal(_)) => unreachable!(
-            r#"Compiler bug! After type checking, a constructor can never align with a literal: that should be a type error!"#
-        ),
-        None => panic!("Compiler error! Empty matrices should not get specialized."),
-    }
-}
-
-/// INVARIANT: (length row == N) ==> (length result == N-1)
-fn specialize_row_by_anything(row: &Row) -> Option<Row> {
-    let mut row = row.clone();
-
-    match row.pop() {
-        Some(Anything) => Some(row),
-        _ => None,
-    }
-}
-
-/// ALL CONSTRUCTORS ARE PRESENT?
-
-pub enum Complete {
-    Yes(Vec<Ctor>),
-    No,
-}
-
-fn is_complete(matrix: &PatternMatrix) -> Complete {
-    let ctors = collect_ctors(matrix);
-    let length = ctors.len();
-    let mut it = ctors.into_iter();
-
-    match it.next() {
-        None => Complete::No,
-        Some((_, Union { alternatives, .. })) => {
-            if length == alternatives.len() {
-                Complete::Yes(alternatives)
-            } else {
-                Complete::No
-            }
-        }
-    }
-}
-
-/// COLLECT CTORS
-
-type RefPatternMatrix = [Vec<Pattern>];
-type PatternMatrix = Vec<Vec<Pattern>>;
-type Row = Vec<Pattern>;
-
-fn collect_ctors(matrix: &RefPatternMatrix) -> MutMap<TagId, Union> {
-    let mut ctors = MutMap::default();
-
-    for row in matrix {
-        if let Some(Ctor(union, id, _)) = row.get(row.len() - 1) {
-            ctors.insert(*id, union.clone());
-        }
-    }
-
-    ctors
-}

compiler/mono/src/ir.rs

@@ -1,6 +1,5 @@
 #![allow(clippy::manual_map)]
 
-use crate::exhaustive::{Ctor, Guard, RenderAs, TagId};
 use crate::layout::{
     Builtin, ClosureRepresentation, LambdaSet, Layout, LayoutCache, LayoutProblem,
     RawFunctionLayout, TagIdIntType, UnionLayout, WrappedVariant,
@@ -10,6 +9,7 @@ use bumpalo::Bump;
 use roc_builtins::bitcode::{FloatWidth, IntWidth};
 use roc_can::expr::{ClosureData, IntValue};
 use roc_collections::all::{default_hasher, BumpMap, BumpMapDefault, MutMap};
+use roc_exhaustive::{Ctor, Guard, RenderAs, TagId};
 use roc_module::ident::{ForeignSymbol, Lowercase, TagName};
 use roc_module::low_level::LowLevel;
 use roc_module::symbol::{IdentIds, ModuleId, Symbol};
@@ -95,7 +95,7 @@ pub enum OptLevel {
 
 #[derive(Clone, Debug, PartialEq)]
 pub enum MonoProblem {
-    PatternProblem(crate::exhaustive::Error),
+    PatternProblem(roc_exhaustive::Error),
 }
 
 #[derive(Debug, Clone, Copy)]
@@ -1895,7 +1895,7 @@ fn patterns_to_when<'a>(
     // see https://github.com/rtfeldman/roc/issues/786
     // this must be fixed when moving exhaustiveness checking to the new canonical AST
     for (pattern_var, pattern) in patterns.into_iter() {
-        let context = crate::exhaustive::Context::BadArg;
+        let context = roc_exhaustive::Context::BadArg;
         let mono_pattern = match from_can_pattern(env, layout_cache, &pattern.value) {
             Ok((pat, _assignments)) => {
                 // Don't apply any assignments (e.g. to initialize optional variables) yet.
@@ -1921,7 +1921,7 @@ fn patterns_to_when<'a>(
             pattern.region,
             &[(
                 Loc::at(pattern.region, mono_pattern),
-                crate::exhaustive::Guard::NoGuard,
+                roc_exhaustive::Guard::NoGuard,
             )],
             context,
         ) {
@@ -3279,12 +3279,12 @@ pub fn with_hole<'a>(
                         }
                     };
 
-                let context = crate::exhaustive::Context::BadDestruct;
+                let context = roc_exhaustive::Context::BadDestruct;
                 match crate::exhaustive::check(
                     def.loc_pattern.region,
                     &[(
                         Loc::at(def.loc_pattern.region, mono_pattern.clone()),
-                        crate::exhaustive::Guard::NoGuard,
+                        roc_exhaustive::Guard::NoGuard,
                     )],
                     context,
                 ) {
@@ -5619,12 +5619,12 @@ pub fn from_can<'a>(
                     hole,
                 )
             } else {
-                let context = crate::exhaustive::Context::BadDestruct;
+                let context = roc_exhaustive::Context::BadDestruct;
                 match crate::exhaustive::check(
                     def.loc_pattern.region,
                     &[(
                         Loc::at(def.loc_pattern.region, mono_pattern.clone()),
-                        crate::exhaustive::Guard::NoGuard,
+                        roc_exhaustive::Guard::NoGuard,
                     )],
                     context,
                 ) {
@@ -5750,11 +5750,11 @@ fn to_opt_branches<'a>(
     // NOTE exhaustiveness is checked after the construction of all the branches
     // In contrast to elm (currently), we still do codegen even if a pattern is non-exhaustive.
     // So we not only report exhaustiveness errors, but also correct them
-    let context = crate::exhaustive::Context::BadCase;
+    let context = roc_exhaustive::Context::BadCase;
     match crate::exhaustive::check(region, &loc_branches, context) {
         Ok(_) => {}
         Err(errors) => {
-            use crate::exhaustive::Error::*;
+            use roc_exhaustive::Error::*;
             let mut is_not_exhaustive = false;
             let mut overlapping_branches = std::vec::Vec::new();
 
@@ -7657,12 +7657,12 @@ pub enum Pattern<'a> {
     BitLiteral {
         value: bool,
         tag_name: TagName,
-        union: crate::exhaustive::Union,
+        union: roc_exhaustive::Union,
     },
     EnumLiteral {
         tag_id: u8,
         tag_name: TagName,
-        union: crate::exhaustive::Union,
+        union: roc_exhaustive::Union,
     },
     StrLiteral(Box<str>),
 
@@ -7676,7 +7676,7 @@ pub enum Pattern<'a> {
         tag_id: TagIdIntType,
         arguments: Vec<'a, (Pattern<'a>, Layout<'a>)>,
         layout: UnionLayout<'a>,
-        union: crate::exhaustive::Union,
+        union: roc_exhaustive::Union,
     },
     OpaqueUnwrap {
         opaque: Symbol,
@@ -7817,8 +7817,8 @@ fn from_can_pattern_help<'a>(
             arguments,
             ..
         } => {
-            use crate::exhaustive::Union;
             use crate::layout::UnionVariant::*;
+            use roc_exhaustive::Union;
 
             let res_variant =
                 crate::layout::union_sorted_tags(env.arena, *whole_var, env.subs, env.target_info)
@@ -7883,7 +7883,7 @@ fn from_can_pattern_help<'a>(
                         })
                     }
 
-                    let union = crate::exhaustive::Union {
+                    let union = roc_exhaustive::Union {
                         render_as: RenderAs::Tag,
                         alternatives: ctors,
                     };
@@ -7974,7 +7974,7 @@ fn from_can_pattern_help<'a>(
                                 })
                             }
 
-                            let union = crate::exhaustive::Union {
+                            let union = roc_exhaustive::Union {
                                 render_as: RenderAs::Tag,
                                 alternatives: ctors,
                             };
@@ -8026,7 +8026,7 @@ fn from_can_pattern_help<'a>(
                                 })
                             }
 
-                            let union = crate::exhaustive::Union {
+                            let union = roc_exhaustive::Union {
                                 render_as: RenderAs::Tag,
                                 alternatives: ctors,
                             };
@@ -8069,7 +8069,7 @@ fn from_can_pattern_help<'a>(
                                 arity: fields.len(),
                             });
 
-                            let union = crate::exhaustive::Union {
+                            let union = roc_exhaustive::Union {
                                 render_as: RenderAs::Tag,
                                 alternatives: ctors,
                             };
@@ -8139,7 +8139,7 @@ fn from_can_pattern_help<'a>(
                                 });
                             }
 
-                            let union = crate::exhaustive::Union {
+                            let union = roc_exhaustive::Union {
                                 render_as: RenderAs::Tag,
                                 alternatives: ctors,
                             };
@@ -8194,7 +8194,7 @@ fn from_can_pattern_help<'a>(
                                 arity: other_fields.len() - 1,
                             });
 
-                            let union = crate::exhaustive::Union {
+                            let union = roc_exhaustive::Union {
                                 render_as: RenderAs::Tag,
                                 alternatives: ctors,
                             };

reporting/Cargo.toml

@@ -7,6 +7,7 @@ edition = "2018"
 
 [dependencies]
 roc_collections = { path = "../compiler/collections" }
+roc_exhaustive = { path = "../compiler/exhaustive" }
 roc_region = { path = "../compiler/region" }
 roc_module = { path = "../compiler/module" }
 roc_parse = { path = "../compiler/parse" }

reporting/src/error/mono.rs

@@ -10,8 +10,8 @@ pub fn mono_problem<'b>(
     filename: PathBuf,
     problem: roc_mono::ir::MonoProblem,
 ) -> Report<'b> {
-    use roc_mono::exhaustive::Context::*;
-    use roc_mono::exhaustive::Error::*;
+    use roc_exhaustive::Context::*;
+    use roc_exhaustive::Error::*;
     use roc_mono::ir::MonoProblem::*;
 
     match problem {
@@ -121,7 +121,7 @@ pub fn mono_problem<'b>(
 
 pub fn unhandled_patterns_to_doc_block<'b>(
     alloc: &'b RocDocAllocator<'b>,
-    patterns: Vec<roc_mono::exhaustive::Pattern>,
+    patterns: Vec<roc_exhaustive::Pattern>,
 ) -> RocDocBuilder<'b> {
     alloc
         .vcat(patterns.into_iter().map(|v| pattern_to_doc(alloc, v)))
@@ -131,19 +131,19 @@ pub fn unhandled_patterns_to_doc_block<'b>(
 
 fn pattern_to_doc<'b>(
     alloc: &'b RocDocAllocator<'b>,
-    pattern: roc_mono::exhaustive::Pattern,
+    pattern: roc_exhaustive::Pattern,
 ) -> RocDocBuilder<'b> {
     pattern_to_doc_help(alloc, pattern, false)
 }
 
 fn pattern_to_doc_help<'b>(
     alloc: &'b RocDocAllocator<'b>,
-    pattern: roc_mono::exhaustive::Pattern,
+    pattern: roc_exhaustive::Pattern,
     in_type_param: bool,
 ) -> RocDocBuilder<'b> {
-    use roc_mono::exhaustive::Literal::*;
-    use roc_mono::exhaustive::Pattern::*;
-    use roc_mono::exhaustive::RenderAs;
+    use roc_exhaustive::Literal::*;
+    use roc_exhaustive::Pattern::*;
+    use roc_exhaustive::RenderAs;
 
     match pattern {
         Anything => alloc.text("_"),