Suggest similar table/column/indexes names on missing errors

ARCHITECTURE.md

@@ -95,6 +95,11 @@ There are two authentication methods:
 - **None:** no authentication needed.
 - **Native:** authentication performed with user and password. Read, write or all permissions can be specified for those users. It can also be configured using a JSON file.
 
+## `internal/similartext`
+
+Contains a function to `Find` the most similar name from an
+array to a given one using the Levenshtein distance algorithm. Used for suggestions on errors.
+
 ## `internal/regex`
 
 go-mysql-server has multiple regular expression engines, such as oniguruma and the standard Go regexp engine. In this package, a common interface for regular expression engines is defined.
@@ -134,4 +139,4 @@ After parsing, the obtained execution plan is analyzed using the analyzer define
 
 If indexes can be used, the analyzer will transform the query so it uses indexes reading from the drivers in `sql/index` (in this case `sql/index/pilosa` because there is only one driver).
 
-Once the plan is analyzed, it will be executed recursively from the top of the tree to the bottom to obtain the results and they will be sent back to the client using the MySQL wire protocol.
+Once the plan is analyzed, it will be executed recursively from the top of the tree to the bottom to obtain the results and they will be sent back to the client using the MySQL wire protocol.

internal/similartext/similartext.go

@@ -0,0 +1,107 @@
+package similartext
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+)
+
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}
+
+// DistanceForStrings returns the edit distance between source and target.
+// It has a runtime proportional to len(source) * len(target) and memory use
+// proportional to len(target).
+// Taken (simplified, for strings and with default options) from:
+// https://github.com/texttheater/golang-levenshtein
+func distanceForStrings(source, target string) int {
+	height := len(source) + 1
+	width := len(target) + 1
+	matrix := make([][]int, 2)
+
+	for i := 0; i < 2; i++ {
+		matrix[i] = make([]int, width)
+		matrix[i][0] = i
+	}
+	for j := 1; j < width; j++ {
+		matrix[0][j] = j
+	}
+
+	for i := 1; i < height; i++ {
+		cur := matrix[i%2]
+		prev := matrix[(i-1)%2]
+		cur[0] = i
+		for j := 1; j < width; j++ {
+			delCost := prev[j] + 1
+			matchSubCost := prev[j-1]
+			if source[i-1] != target[j-1] {
+				matchSubCost += 2
+			}
+			insCost := cur[j-1] + 1
+			cur[j] = min(delCost, min(matchSubCost, insCost))
+		}
+	}
+	return matrix[(height-1)%2][width-1]
+}
+
+// MaxDistanceIgnored is the maximum Levenshtein distance from which
+// we won't consider a string similar at all and thus will be ignored.
+var DistanceSkipped = 3
+
+// Find returns a string with suggestions for name(s) in `names`
+// similar to the string `src` until a max distance of `DistanceSkipped`.
+func Find(names []string, src string) string {
+	if len(src) == 0 {
+		return ""
+	}
+
+	minDistance := -1
+	matchMap := make(map[int][]string)
+
+	for _, name := range names {
+		dist := distanceForStrings(name, src)
+		if dist >= DistanceSkipped {
+			continue
+		}
+
+		if minDistance == -1 || dist < minDistance {
+			minDistance = dist
+		}
+
+		matchMap[dist] = append(matchMap[dist], name)
+	}
+
+	if len(matchMap) == 0 {
+		return ""
+	}
+
+	return fmt.Sprintf(", maybe you mean %s?",
+		strings.Join(matchMap[minDistance], " or "))
+}
+
+// FindFromMap does the same as Find but taking a map instead
+// of a string array as first argument.
+func FindFromMap(names interface{}, src string) string {
+	rnames := reflect.ValueOf(names)
+	if rnames.Kind() != reflect.Map {
+		panic("Implementation error: non map used as first argument " +
+			"to FindFromMap")
+	}
+
+	t := rnames.Type()
+	if t.Key().Kind() != reflect.String {
+		panic("Implementation error: non string key for map used as " +
+			"first argument to FindFromMap")
+	}
+
+	var namesList []string
+	for _, kv := range rnames.MapKeys() {
+		namesList = append(namesList, kv.String())
+	}
+
+	return Find(namesList, src)
+}

internal/similartext/similartext_test.go

@@ -0,0 +1,52 @@
+package similartext
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFind(t *testing.T) {
+	require := require.New(t)
+
+	var names []string
+	res := Find(names, "")
+	require.Empty(res)
+
+	names = []string{"foo", "bar", "aka", "ake"}
+	res = Find(names, "baz")
+	require.Equal(", maybe you mean bar?", res)
+
+	res = Find(names, "")
+	require.Empty(res)
+
+	res = Find(names, "foo")
+	require.Equal(", maybe you mean foo?", res)
+
+	res = Find(names, "willBeTooDifferent")
+	require.Empty(res)
+
+	res = Find(names, "aki")
+	require.Equal(", maybe you mean aka or ake?", res)
+}
+
+func TestFindFromMap(t *testing.T) {
+	require := require.New(t)
+
+	var names map[string]int
+	res := FindFromMap(names, "")
+	require.Empty(res)
+
+	names = map[string]int {
+		"foo": 1,
+		"bar": 2,
+	}
+	res = FindFromMap(names, "baz")
+	require.Equal(", maybe you mean bar?", res)
+
+	res = FindFromMap(names, "")
+	require.Empty(res)
+
+	res = FindFromMap(names, "foo")
+	require.Equal(", maybe you mean foo?", res)
+}

sql/analyzer/resolve_columns.go

@@ -5,11 +5,12 @@ import (
 	"sort"
 	"strings"
 
-	errors "gopkg.in/src-d/go-errors.v1"
+	"gopkg.in/src-d/go-errors.v1"
 	"gopkg.in/src-d/go-mysql-server.v0/sql"
 	"gopkg.in/src-d/go-mysql-server.v0/sql/expression"
 	"gopkg.in/src-d/go-mysql-server.v0/sql/plan"
 	"gopkg.in/src-d/go-vitess.v1/vt/sqlparser"
+	"gopkg.in/src-d/go-mysql-server.v0/internal/similartext"
 )
 
 func checkAliases(ctx *sql.Context, a *Analyzer, n sql.Node) (sql.Node, error) {
@@ -202,7 +203,12 @@ func qualifyColumns(ctx *sql.Context, a *Analyzer, n sql.Node) (sql.Node, error)
 					}
 
 					if _, ok := tables[col.Table()]; !ok {
-						return nil, sql.ErrTableNotFound.New(col.Table())
+						if len(tables) == 0 {
+							return nil, sql.ErrTableNotFound.New(col.Table())
+						}
+
+						similar := similartext.FindFromMap(tables, col.Table())
+						return nil, sql.ErrTableNotFound.New(col.Table() + similar)
 					}
 				}
 
@@ -406,11 +412,16 @@ func resolveColumns(ctx *sql.Context, a *Analyzer, n sql.Node) (sql.Node, error)
 					return &deferredColumn{uc}, nil
 
 				default:
+					if len(colMap) == 0 {
+						return nil, ErrColumnNotFound.New(uc.Name())
+					}
+
 					if table != "" {
 						return nil, ErrColumnTableNotFound.New(uc.Table(), uc.Name())
 					}
 
-					return nil, ErrColumnNotFound.New(uc.Name())
+					similar := similartext.FindFromMap(colMap, uc.Name())
+					return nil, ErrColumnNotFound.New(uc.Name() + similar)
 				}
 			}
 

sql/catalog.go

@@ -5,6 +5,8 @@ import (
 	"strings"
 	"sync"
 
+	"gopkg.in/src-d/go-mysql-server.v0/internal/similartext"
+
 	"gopkg.in/src-d/go-errors.v1"
 )
 
@@ -93,14 +95,21 @@ type Databases []Database
 
 // Database returns the Database with the given name if it exists.
 func (d Databases) Database(name string) (Database, error) {
+
+	if len(d) == 0 {
+		return nil, ErrDatabaseNotFound.New(name)
+	}
+
 	name = strings.ToLower(name)
+	var dbNames []string
 	for _, db := range d {
 		if strings.ToLower(db.Name()) == name {
 			return db, nil
 		}
+		dbNames = append(dbNames, db.Name())
 	}
-
-	return nil, ErrDatabaseNotFound.New(name)
+	similar := similartext.Find(dbNames, name)
+	return nil, ErrDatabaseNotFound.New(name + similar)
 }
 
 // Add adds a new database.
@@ -118,6 +127,10 @@ func (d Databases) Table(dbName string, tableName string) (Table, error) {
 	tableName = strings.ToLower(tableName)
 
 	tables := db.Tables()
+	if len(tables) == 0 {
+		return nil, ErrTableNotFound.New(tableName)
+	}
+
 	// Try to get the table by key, but if the name is not the same,
 	// then use the slow path and iterate over all tables comparing
 	// the name.
@@ -129,7 +142,8 @@ func (d Databases) Table(dbName string, tableName string) (Table, error) {
 			}
 		}
 
-		return nil, ErrTableNotFound.New(tableName)
+		similar := similartext.FindFromMap(tables, tableName)
+		return nil, ErrTableNotFound.New(tableName + similar)
 	}
 
 	return table, nil

sql/catalog_test.go

@@ -49,6 +49,10 @@ func TestCatalogDatabase(t *testing.T) {
 	mydb := mem.NewDatabase("foo")
 	c.AddDatabase(mydb)
 
+	db, err = c.Database("flo")
+	require.EqualError(err, "database not found: flo, maybe you mean foo?")
+	require.Nil(db)
+
 	db, err = c.Database("foo")
 	require.NoError(err)
 	require.Equal(mydb, db)
@@ -73,6 +77,10 @@ func TestCatalogTable(t *testing.T) {
 	mytable := mem.NewTable("bar", nil)
 	db.AddTable("bar", mytable)
 
+	table, err = c.Table("foo", "baz")
+	require.EqualError(err, "table not found: baz, maybe you mean bar?")
+	require.Nil(table)
+
 	table, err = c.Table("foo", "bar")
 	require.NoError(err)
 	require.Equal(mytable, table)

sql/functionregistry.go

@@ -2,6 +2,7 @@ package sql
 
 import (
 	"gopkg.in/src-d/go-errors.v1"
+	"gopkg.in/src-d/go-mysql-server.v0/internal/similartext"
 )
 
 // ErrFunctionAlreadyRegistered is thrown when a function is already registered
@@ -203,9 +204,13 @@ func (r FunctionRegistry) MustRegister(fn ...Function) {
 
 // Function returns a function with the given name.
 func (r FunctionRegistry) Function(name string) (Function, error) {
+	if len(r) == 0 {
+		return nil, ErrFunctionNotFound.New(name)
+	}
+
 	if fn, ok := r[name]; ok {
 		return fn, nil
 	}
-
-	return nil, ErrFunctionNotFound.New(name)
+	similar := similartext.FindFromMap(r, name)
+	return nil, ErrFunctionNotFound.New(name + similar)
 }

sql/index.go

@@ -1,6 +1,7 @@
 package sql
 
 import (
+	"gopkg.in/src-d/go-mysql-server.v0/internal/similartext"
 	"io"
 	"strings"
 	"sync"
@@ -548,6 +549,13 @@ func (r *IndexRegistry) AddIndex(
 func (r *IndexRegistry) DeleteIndex(db, id string, force bool) (<-chan struct{}, error) {
 	r.mut.RLock()
 	var key indexKey
+
+	if len(r.indexes) == 0 {
+		return nil, ErrIndexNotFound.New(id)
+	}
+
+	var indexNames []string
+
 	for k, idx := range r.indexes {
 		if strings.ToLower(id) == idx.ID() {
 			if !force && !r.CanRemoveIndex(idx) {
@@ -558,11 +566,13 @@ func (r *IndexRegistry) DeleteIndex(db, id string, force bool) (<-chan struct{},
 			key = k
 			break
 		}
+		indexNames = append(indexNames, idx.ID())
 	}
 	r.mut.RUnlock()
 
 	if key.id == "" {
-		return nil, ErrIndexNotFound.New(id)
+		similar := similartext.Find(indexNames, id)
+		return nil, ErrIndexNotFound.New(id + similar)
 	}
 
 	var done = make(chan struct{}, 1)

sql/plan/drop_index.go

@@ -1,7 +1,8 @@
 package plan
 
 import (
-	errors "gopkg.in/src-d/go-errors.v1"
+	"gopkg.in/src-d/go-errors.v1"
+	"gopkg.in/src-d/go-mysql-server.v0/internal/similartext"
 	"gopkg.in/src-d/go-mysql-server.v0/sql"
 )
 
@@ -51,9 +52,15 @@ func (d *DropIndex) RowIter(ctx *sql.Context) (sql.RowIter, error) {
 		return nil, ErrTableNotNameable.New()
 	}
 
-	table, ok := db.Tables()[n.Name()]
+	tables := db.Tables()
+	table, ok := tables[n.Name()]
 	if !ok {
-		return nil, sql.ErrTableNotFound.New(n.Name())
+		if len(tables) == 0 {
+			return nil, sql.ErrTableNotFound.New(n.Name())
+		}
+
+		similar := similartext.FindFromMap(tables, n.Name())
+		return nil, sql.ErrTableNotFound.New(n.Name() + similar)
 	}
 
 	index := d.Catalog.Index(db.Name(), d.Name)