Introduce the query tree data structure

Cargo.lock

@@ -1277,11 +1277,13 @@ dependencies = [
  "ordered-float",
  "pest 2.1.3 (git+https://github.com/pest-parser/pest.git?rev=51fd1d49f1041f7839975664ef71fe15c7dcaf67)",
  "pest_derive",
+ "rand 0.8.3",
  "rayon",
  "regex",
  "roaring",
  "serde",
  "serde_json",
+ "slice-group-by",
  "smallstr",
  "smallvec",
  "tempfile",

milli/Cargo.toml

@@ -30,6 +30,7 @@ regex = "1.4.3"
 roaring = "0.6.5"
 serde = { version = "1.0.123", features = ["derive"] }
 serde_json = { version = "1.0.62", features = ["preserve_order"] }
+slice-group-by = "0.2.6"
 smallstr =  { version = "0.2.0", features = ["serde"] }
 smallvec = "1.6.1"
 tempfile = "3.2.0"
@@ -48,6 +49,7 @@ log = "0.4.14"
 [dev-dependencies]
 criterion = "0.3.4"
 maplit = "1.0.2"
+rand = "0.8.3"
 
 [build-dependencies]
 fst = "0.4.5"

milli/src/search/mod.rs

@@ -29,6 +29,7 @@ static LEVDIST1: Lazy<LevBuilder> = Lazy::new(|| LevBuilder::new(1, true));
 static LEVDIST2: Lazy<LevBuilder> = Lazy::new(|| LevBuilder::new(2, true));
 
 mod facet;
+mod query_tree;
 
 pub struct Search<'a> {
     query: Option<String>,
@@ -391,3 +392,30 @@ pub struct SearchResult {
     // TODO those documents ids should be associated with their criteria scores.
     pub documents_ids: Vec<DocumentId>,
 }
+
+pub fn word_typos(word: &str, is_prefix: bool, max_typo: u8, fst: &fst::Set<Cow<[u8]>>) -> anyhow::Result<Vec<(String, u8)>> {
+    let dfa = {
+        let lev = match max_typo {
+            0 => &LEVDIST0,
+            1 => &LEVDIST1,
+            _ => &LEVDIST2,
+        };
+
+        if is_prefix {
+            lev.build_prefix_dfa(&word)
+        } else {
+            lev.build_dfa(&word)
+        }
+    };
+
+    let mut derived_words = Vec::new();
+    let mut stream = fst.search_with_state(&dfa).into_stream();
+
+    while let Some((word, state)) = stream.next() {
+        let word = std::str::from_utf8(word)?;
+        let distance = dfa.distance(state);
+        derived_words.push((word.to_string(), distance.to_u8()));
+    }
+
+    Ok(derived_words)
+}

milli/src/search/query_tree.rs

@@ -0,0 +1,887 @@
+#![allow(unused)]
+
+use std::borrow::Cow;
+use std::collections::BTreeMap;
+use std::{fmt, cmp, mem};
+
+use meilisearch_tokenizer::{TokenKind, tokenizer::TokenStream};
+use roaring::RoaringBitmap;
+use slice_group_by::GroupBy;
+
+use crate::Index;
+
+type IsOptionalWord = bool;
+type IsPrefix = bool;
+
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub enum Operation {
+    And(Vec<Operation>),
+    Consecutive(Vec<Operation>),
+    Or(IsOptionalWord, Vec<Operation>),
+    Query(Query),
+}
+
+impl fmt::Debug for Operation {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fn pprint_tree(f: &mut fmt::Formatter<'_>, op: &Operation, depth: usize) -> fmt::Result {
+            match op {
+                Operation::And(children) => {
+                    writeln!(f, "{:1$}AND", "", depth * 2)?;
+                    children.iter().try_for_each(|c| pprint_tree(f, c, depth + 1))
+                },
+                Operation::Consecutive(children) => {
+                    writeln!(f, "{:1$}CONSECUTIVE", "", depth * 2)?;
+                    children.iter().try_for_each(|c| pprint_tree(f, c, depth + 1))
+                },
+                Operation::Or(true, children) => {
+                    writeln!(f, "{:1$}OR(WORD)", "", depth * 2)?;
+                    children.iter().try_for_each(|c| pprint_tree(f, c, depth + 1))
+                },
+                Operation::Or(false, children) => {
+                    writeln!(f, "{:1$}OR", "", depth * 2)?;
+                    children.iter().try_for_each(|c| pprint_tree(f, c, depth + 1))
+                },
+                Operation::Query(query) => writeln!(f, "{:2$}{:?}", "", query, depth * 2),
+            }
+        }
+
+        pprint_tree(f, self, 0)
+    }
+}
+
+impl Operation {
+    fn tolerant(prefix: IsPrefix, s: &str) -> Operation {
+        Operation::Query(Query { prefix, kind: QueryKind::tolerant(2, s.to_string()) })
+    }
+
+    fn exact(prefix: IsPrefix, s: &str) -> Operation {
+        Operation::Query(Query { prefix, kind: QueryKind::exact(s.to_string()) })
+    }
+
+    fn phrase(words: Vec<String>) -> Operation {
+        Operation::consecutive(
+            words.into_iter().map(|s| {
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact(s) })
+            }).collect()
+        )
+    }
+
+    fn and(mut ops: Vec<Self>) -> Self {
+        if ops.len() == 1 {
+            ops.pop().unwrap()
+        } else {
+            Self::And(ops)
+        }
+    }
+
+    pub fn or(word_branch: IsOptionalWord, mut ops: Vec<Self>) -> Self {
+        if ops.len() == 1 {
+            ops.pop().unwrap()
+        } else {
+            Self::Or(word_branch, ops)
+        }
+    }
+
+    fn consecutive(mut ops: Vec<Self>) -> Self {
+        if ops.len() == 1 {
+            ops.pop().unwrap()
+        } else {
+            Self::Consecutive(ops)
+        }
+    }
+}
+
+#[derive(Clone, Eq, PartialEq, Hash)]
+pub struct Query {
+    pub prefix: IsPrefix,
+    pub kind: QueryKind,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq, Hash)]
+pub enum QueryKind {
+    Tolerant { typo: u8, word: String },
+    Exact { original_typo: u8, word: String },
+}
+
+impl QueryKind {
+    fn exact(word: String) -> Self {
+        QueryKind::Exact { original_typo: 0, word }
+    }
+
+    fn tolerant(typo: u8, word: String) -> Self {
+        QueryKind::Tolerant { typo, word }
+    }
+
+    pub fn typo(&self) -> u8 {
+        match self {
+            QueryKind::Tolerant { typo, .. } => *typo,
+            QueryKind::Exact { original_typo, .. } => *original_typo,
+        }
+    }
+
+    pub fn word(&self) -> &str {
+        match self {
+            QueryKind::Tolerant { word, .. } => word,
+            QueryKind::Exact { word, .. } => word,
+        }
+    }
+}
+
+impl fmt::Debug for Query {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let Query { prefix, kind } = self;
+        let prefix = if *prefix { String::from("Prefix") } else { String::default() };
+        match kind {
+            QueryKind::Exact { word, .. } => {
+                f.debug_struct(&(prefix + "Exact")).field("word", &word).finish()
+            },
+            QueryKind::Tolerant { typo, word } => {
+                f.debug_struct(&(prefix + "Tolerant")).field("word", &word).field("max typo", &typo).finish()
+            },
+        }
+    }
+}
+
+trait Context {
+    fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>>;
+    fn synonyms<S: AsRef<str>>(&self, words: &[S]) -> heed::Result<Option<Vec<Vec<String>>>>;
+}
+
+/// The query tree builder is the interface to build a query tree.
+pub struct QueryTreeBuilder<'a> {
+    rtxn: &'a heed::RoTxn<'a>,
+    index: &'a Index,
+}
+
+impl<'a> Context for QueryTreeBuilder<'a> {
+    fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>> {
+        self.index.word_docids.get(self.rtxn, word)
+    }
+
+    fn synonyms<S: AsRef<str>>(&self, _words: &[S]) -> heed::Result<Option<Vec<Vec<String>>>> {
+        Ok(None)
+    }
+}
+
+impl<'a> QueryTreeBuilder<'a> {
+    /// Create a `QueryTreeBuilder` from a heed ReadOnly transaction `rtxn`
+    /// and an Index `index`.
+    pub fn new(rtxn: &'a heed::RoTxn<'a>, index: &'a Index) -> Self {
+        Self { rtxn, index }
+    }
+
+    /// Build the query tree:
+    /// - if `optional_words` is set to `false` the query tree will be
+    ///   generated forcing all query words to be present in each matching documents
+    ///   (the criterion `words` will be ignored)
+    /// - if `authorize_typos` is set to `false` the query tree will be generated
+    ///   forcing all query words to match documents without any typo
+    ///   (the criterion `typo` will be ignored)
+    pub fn build(
+        &self,
+        optional_words: bool,
+        authorize_typos: bool,
+        query: TokenStream,
+    ) -> anyhow::Result<Option<Operation>>
+    {
+        let primitive_query = create_primitive_query(query);
+        if !primitive_query.is_empty() {
+            create_query_tree(self, optional_words, authorize_typos, primitive_query).map(Some)
+        } else {
+            Ok(None)
+        }
+    }
+}
+
+/// Split the word depending on the frequency of subwords in the database documents.
+fn split_best_frequency<'a>(ctx: &impl Context, word: &'a str) -> heed::Result<Option<Operation>> {
+    let chars = word.char_indices().skip(1);
+    let mut best = None;
+
+    for (i, _) in chars {
+        let (left, right) = word.split_at(i);
+
+        let left_freq = ctx.word_docids(left)?.map(|docids| docids.len()).unwrap_or(0);
+        let right_freq = ctx.word_docids(right)?.map(|docids| docids.len()).unwrap_or(0);
+
+        let min_freq = cmp::min(left_freq, right_freq);
+        if min_freq != 0 && best.map_or(true, |(old, _, _)| min_freq > old) {
+            best = Some((min_freq, left, right));
+        }
+    }
+
+    Ok(best.map(|(_, left, right)| Operation::Consecutive(
+        vec![
+            Operation::Query(Query { prefix: false, kind: QueryKind::exact(left.to_string()) }),
+            Operation::Query(Query { prefix: false, kind: QueryKind::exact(right.to_string()) })
+        ]
+    )))
+}
+
+/// Return the `QueryKind` of a word depending on `authorize_typos`
+/// and the provided word length.
+fn typos(word: String, authorize_typos: bool) -> QueryKind {
+    if authorize_typos {
+        match word.len() {
+            0..=4 => QueryKind::exact(word),
+            5..=8 => QueryKind::tolerant(1, word),
+            _     => QueryKind::tolerant(2, word),
+        }
+    } else {
+        QueryKind::exact(word)
+    }
+}
+
+/// Fetch synonyms from the `Context` for the provided word
+/// and create the list of operations for the query tree
+fn synonyms(ctx: &impl Context, word: &[&str]) -> heed::Result<Option<Vec<Operation>>> {
+    let synonyms = ctx.synonyms(word)?;
+
+    Ok(synonyms.map(|synonyms| {
+        synonyms.into_iter().map(|synonym| {
+            let words = synonym.into_iter().map(|word| {
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact(word) })
+            }).collect();
+            Operation::and(words)
+        }).collect()
+    }))
+}
+
+/// The query tree builder is the interface to build a query tree.
+pub struct MatchingWords {
+    inner: BTreeMap<String, IsPrefix>
+}
+
+impl MatchingWords {
+    /// List all words which can be considered as a match for the query tree.
+    pub fn from_query_tree(tree: &Operation, fst: &fst::Set<Cow<[u8]>>) -> Self {
+        Self { inner: fetch_words(tree, fst).into_iter().collect() }
+    }
+
+    /// Return true if the word match.
+    pub fn is_match(&self, word: &str) -> bool {
+        fn first_char(s: &str) -> Option<&str> {
+            s.chars().next().map(|c| &s[..c.len_utf8()])
+        }
+
+        match first_char(word) {
+            Some(first) => {
+                let left = first.to_owned();
+                let right = word.to_owned();
+                self.inner.range(left..=right).any(|(w, is_prefix)| *is_prefix || *w == word)
+            },
+            None => false
+        }
+    }
+}
+
+type FetchedWords = Vec<(String, IsPrefix)>;
+
+/// Lists all words which can be considered as a match for the query tree.
+fn fetch_words(tree: &Operation, fst: &fst::Set<Cow<[u8]>>) -> FetchedWords {
+    fn resolve_branch(tree: &[Operation], fst: &fst::Set<Cow<[u8]>>) -> FetchedWords {
+        tree.iter().map(|op| resolve_ops(op, fst)).flatten().collect()
+    }
+
+    fn resolve_query(query: &Query, fst: &fst::Set<Cow<[u8]>>) -> FetchedWords {
+        match query.kind.clone() {
+            QueryKind::Exact { word, .. } => vec![(word, query.prefix)],
+            QueryKind::Tolerant { typo, word } => {
+                if let Ok(words) = super::word_typos(&word, query.prefix, typo, fst) {
+                    words.into_iter().map(|(w, _)| (w, query.prefix)).collect()
+                } else {
+                    vec![(word, query.prefix)]
+                }
+            }
+        }
+    }
+
+    fn resolve_ops(tree: &Operation, fst: &fst::Set<Cow<[u8]>>) -> FetchedWords {
+        match tree {
+            Operation::Or(_, ops) | Operation::And(ops) | Operation::Consecutive(ops) => {
+                resolve_branch(ops.as_slice(), fst)
+            },
+            Operation::Query(ops) => {
+                resolve_query(ops, fst)
+            },
+        }
+    }
+
+    let mut words = resolve_ops(tree, fst);
+    words.sort_unstable();
+    words.dedup();
+    words
+}
+
+/// Main function that creates the final query tree from the primitive query.
+fn create_query_tree(
+    ctx: &impl Context,
+    optional_words: bool,
+    authorize_typos: bool,
+    query: PrimitiveQuery,
+) -> anyhow::Result<Operation>
+{
+    /// Matches on the `PrimitiveQueryPart` and create an operation from it.
+    fn resolve_primitive_part(
+        ctx: &impl Context,
+        authorize_typos: bool,
+        part: PrimitiveQueryPart,
+    ) -> anyhow::Result<Operation>
+    {
+        match part {
+            // 1. try to split word in 2
+            // 2. try to fetch synonyms
+            // 3. create an operation containing the word
+            // 4. wrap all in an OR operation
+            PrimitiveQueryPart::Word(word, prefix) => {
+                let mut children = synonyms(ctx, &[&word])?.unwrap_or_default();
+                if let Some(child) = split_best_frequency(ctx, &word)? {
+                    children.push(child);
+                }
+                children.push(Operation::Query(Query { prefix, kind: typos(word, authorize_typos) }));
+                Ok(Operation::or(false, children))
+            },
+            // create a CONSECUTIVE operation wrapping all word in the phrase
+            PrimitiveQueryPart::Phrase(words) => {
+                Ok(Operation::phrase(words))
+            },
+        }
+    }
+
+    /// Create all ngrams 1..=3 generating query tree branches.
+    fn ngrams(
+        ctx: &impl Context,
+        authorize_typos: bool,
+        query: &[PrimitiveQueryPart],
+    ) -> anyhow::Result<Operation>
+    {
+        const MAX_NGRAM: usize = 3;
+        let mut op_children = Vec::new();
+
+        for sub_query in query.linear_group_by(|a, b| !(a.is_phrase() || b.is_phrase()) ) {
+            let mut or_op_children = Vec::new();
+
+            for ngram in 1..=MAX_NGRAM.min(sub_query.len()) {
+                if let Some(group) = sub_query.get(..ngram) {
+                    let mut and_op_children = Vec::new();
+                    let tail = &sub_query[ngram..];
+                    let is_last = tail.is_empty();
+
+                    match group {
+                        [part] => {
+                            let operation = resolve_primitive_part(ctx, authorize_typos, part.clone())?;
+                            and_op_children.push(operation);
+                        },
+                        words => {
+                            let is_prefix = words.last().map(|part| part.is_prefix()).unwrap_or(false);
+                            let words: Vec<_> = words.iter().filter_map(| part| {
+                                if let PrimitiveQueryPart::Word(word, _) = part {
+                                    Some(word.as_str())
+                                } else {
+                                    None
+                                }
+                            }).collect();
+                            let mut operations = synonyms(ctx, &words)?.unwrap_or_default();
+                            let concat = words.concat();
+                            let query = Query { prefix: is_prefix, kind: typos(concat, authorize_typos) };
+                            operations.push(Operation::Query(query));
+                            and_op_children.push(Operation::or(false, operations));
+                        }
+                    }
+
+                    if !is_last {
+                        let ngrams = ngrams(ctx, authorize_typos, tail)?;
+                        and_op_children.push(ngrams);
+                    }
+                    or_op_children.push(Operation::and(and_op_children));
+                }
+            }
+            op_children.push(Operation::or(false, or_op_children));
+        }
+
+        Ok(Operation::and(op_children))
+    }
+
+    /// Create a new branch removing the last non-phrase query parts.
+    fn optional_word(
+        ctx: &impl Context,
+        authorize_typos: bool,
+        query: PrimitiveQuery,
+    ) -> anyhow::Result<Operation>
+    {
+        let word_count = query.iter().filter(|part| !part.is_phrase()).count();
+        let mut operation_children = Vec::new();
+
+        for count in (1..=word_count).rev() {
+            let mut tmp_count = 0;
+
+            // keep only the N firsts non-quoted words, where N = count
+            // quoted words are allways kept
+            let query: Vec<_> = query.iter().cloned().filter(|part| {
+                if !part.is_phrase()  {
+                    tmp_count += 1;
+                    tmp_count <= count
+                } else { true }
+            }).collect();
+
+            let ngrams = ngrams(ctx, authorize_typos, query.as_slice())?;
+            operation_children.push(ngrams);
+        }
+
+        Ok(Operation::or(true, operation_children))
+    }
+
+    if optional_words {
+        optional_word(ctx, authorize_typos, query)
+    } else {
+        ngrams(ctx, authorize_typos, query.as_slice())
+    }
+}
+
+type PrimitiveQuery = Vec<PrimitiveQueryPart>;
+
+#[derive(Debug, Clone)]
+enum PrimitiveQueryPart {
+    Phrase(Vec<String>),
+    Word(String, IsPrefix),
+}
+
+impl PrimitiveQueryPart {
+    fn is_phrase(&self) -> bool {
+        matches!(self, Self::Phrase(_))
+    }
+
+    fn is_prefix(&self) -> bool {
+        matches!(self, Self::Word(_, is_prefix) if *is_prefix)
+    }
+}
+
+/// Create primitive query from tokenized query string,
+/// the primitive query is an intermediate state to build the query tree.
+fn create_primitive_query(query: TokenStream) -> PrimitiveQuery {
+    let mut primitive_query = Vec::new();
+    let mut phrase = Vec::new();
+    let mut quoted = false;
+
+    let mut peekable = query.peekable();
+    while let Some(token) = peekable.next() {
+        match token.kind {
+            TokenKind::Word => {
+                // 1. if the word is quoted we push it in a phrase-buffer waiting for the ending quote,
+                // 2. if the word is not the last token of the query we push it as a non-prefix word,
+                // 3. if the word is the last token of the query we push it as a prefix word.
+                if quoted {
+                    phrase.push(token.word.to_string());
+                } else if peekable.peek().is_some() {
+                    primitive_query.push(PrimitiveQueryPart::Word(token.word.to_string(), false));
+                } else {
+                    primitive_query.push(PrimitiveQueryPart::Word(token.word.to_string(), true));
+                }
+            },
+            TokenKind::Separator(_) => {
+                let quote_count = token.word.chars().filter(|&s| s == '"').count();
+                // swap quoted state if we encounter a double quote
+                if quote_count % 2 != 0 {
+                    quoted = !quoted;
+                }
+                if !phrase.is_empty() && quote_count > 0 {
+                    primitive_query.push(PrimitiveQueryPart::Phrase(mem::take(&mut phrase)));
+                }
+            },
+            _ => (),
+        }
+    }
+
+    // If a quote is never closed, we consider all of the end of the query as a phrase.
+    if !phrase.is_empty() {
+        primitive_query.push(PrimitiveQueryPart::Phrase(mem::take(&mut phrase)));
+    }
+
+    primitive_query
+}
+
+#[cfg(test)]
+mod test {
+    use fst::Set;
+    use maplit::hashmap;
+    use meilisearch_tokenizer::{Analyzer, AnalyzerConfig};
+    use rand::{Rng, SeedableRng, rngs::StdRng};
+
+    use super::*;
+    use std::collections::HashMap;
+    #[derive(Debug)]
+    struct TestContext {
+        synonyms: HashMap<Vec<String>, Vec<Vec<String>>>,
+        postings: HashMap<String, RoaringBitmap>,
+    }
+
+    impl TestContext {
+        fn build(
+            &self,
+            optional_words: bool,
+            authorize_typos: bool,
+            query: TokenStream,
+        ) -> anyhow::Result<Option<Operation>>
+        {
+            let primitive_query = create_primitive_query(query);
+            if !primitive_query.is_empty() {
+                create_query_tree(self, optional_words, authorize_typos, primitive_query).map(Some)
+            } else {
+                Ok(None)
+            }
+        }
+    }
+
+    impl Context for TestContext {
+        fn word_docids(&self, word: &str) -> heed::Result<Option<RoaringBitmap>> {
+            Ok(self.postings.get(word).cloned())
+        }
+
+        fn synonyms<S: AsRef<str>>(&self, words: &[S]) -> heed::Result<Option<Vec<Vec<String>>>> {
+            let words: Vec<_> = words.iter().map(|s| s.as_ref().to_owned()).collect();
+            Ok(self.synonyms.get(&words).cloned())
+        }
+    }
+
+    impl Default for TestContext {
+
+        fn default() -> TestContext {
+            let mut rng = StdRng::seed_from_u64(102);
+            let rng = &mut rng;
+
+            fn random_postings<R: Rng>(rng: &mut R, len: usize) -> RoaringBitmap {
+                let mut values = Vec::<u32>::with_capacity(len);
+                while values.len() != len {
+                    values.push(rng.gen());
+                }
+                values.sort_unstable();
+
+                RoaringBitmap::from_sorted_iter(values.into_iter())
+            }
+
+            TestContext {
+                synonyms: hashmap!{
+                    vec![String::from("hello")] => vec![
+                        vec![String::from("hi")],
+                        vec![String::from("good"), String::from("morning")],
+                    ],
+                    vec![String::from("world")] => vec![
+                        vec![String::from("earth")],
+                        vec![String::from("nature")],
+                    ],
+                    // new york city
+                    vec![String::from("nyc")] => vec![
+                        vec![String::from("new"), String::from("york")],
+                        vec![String::from("new"), String::from("york"), String::from("city")],
+                    ],
+                    vec![String::from("new"), String::from("york")] => vec![
+                        vec![String::from("nyc")],
+                        vec![String::from("new"), String::from("york"), String::from("city")],
+                    ],
+                    vec![String::from("new"), String::from("york"), String::from("city")] => vec![
+                        vec![String::from("nyc")],
+                        vec![String::from("new"), String::from("york")],
+                    ],
+                },
+                postings: hashmap!{
+                    String::from("hello")      => random_postings(rng,   1500),
+                    String::from("hi")         => random_postings(rng,   4000),
+                    String::from("word")       => random_postings(rng,   2500),
+                    String::from("split")      => random_postings(rng,    400),
+                    String::from("ngrams")     => random_postings(rng,   1400),
+                    String::from("world")      => random_postings(rng, 15_000),
+                    String::from("earth")      => random_postings(rng,   8000),
+                    String::from("2021")       => random_postings(rng,    100),
+                    String::from("2020")       => random_postings(rng,    500),
+                    String::from("is")         => random_postings(rng, 50_000),
+                    String::from("this")       => random_postings(rng, 50_000),
+                    String::from("good")       => random_postings(rng,   1250),
+                    String::from("morning")    => random_postings(rng,    125),
+                },
+            }
+        }
+    }
+
+    #[test]
+    fn prefix() {
+        let query = "hey friends";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+                Operation::Query(Query { prefix: true, kind: QueryKind::tolerant(1, "friends".to_string()) }),
+            ]),
+            Operation::Query(Query { prefix: true, kind: QueryKind::tolerant(2, "heyfriends".to_string()) }),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn no_prefix() {
+        let query = "hey friends ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+                Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "friends".to_string()) }),
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(2, "heyfriends".to_string()) }),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn synonyms() {
+        let query = "hello world ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Or(false, vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("hi".to_string()) }),
+                    Operation::And(vec![
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("good".to_string()) }),
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("morning".to_string()) }),
+                    ]),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "hello".to_string()) }),
+                ]),
+                Operation::Or(false, vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("earth".to_string()) }),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("nature".to_string()) }),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "world".to_string()) }),
+                ]),
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(2, "helloworld".to_string()) }),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn complex_synonyms() {
+        let query = "new york city ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("new".to_string()) }),
+                Operation::Or(false, vec![
+                    Operation::And(vec![
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("york".to_string()) }),
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("city".to_string()) }),
+                    ]),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "yorkcity".to_string()) }),
+                ]),
+            ]),
+            Operation::And(vec![
+                Operation::Or(false, vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("nyc".to_string()) }),
+                    Operation::And(vec![
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("new".to_string()) }),
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("york".to_string()) }),
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("city".to_string()) }),
+                    ]),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "newyork".to_string()) }),
+                ]),
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("city".to_string()) }),
+            ]),
+            Operation::Or(false, vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("nyc".to_string()) }),
+                Operation::And(vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("new".to_string()) }),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("york".to_string()) }),
+                ]),
+                Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(2, "newyorkcity".to_string()) }),
+            ]),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn ngrams() {
+        let query = "n grams ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("n".to_string()) }),
+                Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "grams".to_string()) }),
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "ngrams".to_string()) }),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn word_split() {
+        let query = "wordsplit fish ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Or(false, vec![
+                    Operation::Consecutive(vec![
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("word".to_string()) }),
+                        Operation::Query(Query { prefix: false, kind: QueryKind::exact("split".to_string()) }),
+                    ]),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(2, "wordsplit".to_string()) }),
+                ]),
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("fish".to_string()) })
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(2, "wordsplitfish".to_string()) }),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn phrase() {
+        let query = "\"hey friends\" \" \" \"wooop";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::And(vec![
+            Operation::Consecutive(vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("friends".to_string()) }),
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::exact("wooop".to_string()) }),
+        ]);
+
+        let query_tree = TestContext::default().build(false, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn optional_word() {
+        let query = "hey my friend ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(true, vec![
+            Operation::Or(false, vec![
+                Operation::And(vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+                    Operation::Or(false, vec![
+                        Operation::And(vec![
+                            Operation::Query(Query { prefix: false, kind: QueryKind::exact("my".to_string()) }),
+                            Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "friend".to_string()) }),
+                        ]),
+                        Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "myfriend".to_string()) })
+                    ])
+                ]),
+                Operation::And(vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "heymy".to_string()) }),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "friend".to_string()) }),
+                ]),
+                Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(2, "heymyfriend".to_string()) }),
+            ]),
+            Operation::Or(false, vec![
+                Operation::And(vec![
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+                    Operation::Query(Query { prefix: false, kind: QueryKind::exact("my".to_string()) }),
+                ]),
+                Operation::Query(Query { prefix: false, kind: QueryKind::tolerant(1, "heymy".to_string()) }),
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+        ]);
+        let query_tree = TestContext::default().build(true, true, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn no_typo() {
+        let query = "hey friends ";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let expected = Operation::Or(false, vec![
+            Operation::And(vec![
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("hey".to_string()) }),
+                Operation::Query(Query { prefix: false, kind: QueryKind::exact("friends".to_string()) }),
+            ]),
+            Operation::Query(Query { prefix: false, kind: QueryKind::exact("heyfriends".to_string()) }),
+        ]);
+        let query_tree = TestContext::default().build(false, false, tokens).unwrap().unwrap();
+
+        assert_eq!(expected, query_tree);
+    }
+
+    #[test]
+    fn fetching_words() {
+        let query = "wordsplit nyc world";
+        let stop_words = &Set::default();
+        let analyzer = Analyzer::new(AnalyzerConfig::default_with_stopwords(stop_words));
+        let result = analyzer.analyze(query);
+        let tokens = result.tokens();
+
+        let context = TestContext::default();
+        let query_tree = context.build(false, true, tokens).unwrap().unwrap();
+
+        let expected = vec![
+            ("city".to_string(), false),
+            ("earth".to_string(), false),
+            ("nature".to_string(), false),
+            ("new".to_string(), false),
+            ("nyc".to_string(), false),
+            ("split".to_string(), false),
+            ("word".to_string(), false),
+            ("word".to_string(), true),
+            ("world".to_string(), true),
+            ("york".to_string(), false),
+
+        ];
+
+        let mut keys = context.postings.keys().collect::<Vec<_>>();
+        keys.sort_unstable();
+        let set = fst::Set::from_iter(keys).unwrap().map_data(|v| Cow::Owned(v)).unwrap();
+
+        let words = fetch_words(&query_tree, &set);
+
+        assert_eq!(expected, words);
+    }
+}