enhancement: Keyword Query Language (KQL) search syntax support (#7043)

* feat(search): introduce search query package

With the increasing complexity of how we organize our resources, the search must also be able to find them using entity properties.

The query package provides the necessary functionality to do this.

This makes it possible to search for resources via KQL, the microsoft spec is largely covered and can be used for this.

In the current state, the legacy query language is still used, in a future update this will be deprecated and KQL will become the standard

services/search/pkg/query/ast/ast.go

@@ -0,0 +1,63 @@
+// Package ast provides available ast nodes.
+package ast
+
+// Node represents abstract syntax tree node
+type Node interface {
+	Location() *Location
+}
+
+// Position represents a specific location in the source
+type Position struct {
+	Line   int
+	Column int
+}
+
+// Location represents the location of a node in the AST
+type Location struct {
+	Start  Position `json:"start"`
+	End    Position `json:"end"`
+	Source *string  `json:"source,omitempty"`
+}
+
+// Base contains shared node attributes
+// each node should inherit from this
+type Base struct {
+	Loc *Location
+}
+
+// Location is the source location of the Node
+func (b *Base) Location() *Location { return b.Loc }
+
+// Ast represents the query - node structure as abstract syntax tree
+type Ast struct {
+	*Base
+	Nodes []Node `json:"body"`
+}
+
+// StringNode represents a string value
+type StringNode struct {
+	*Base
+	Key   string
+	Value string
+}
+
+// BooleanNode represents a bool value
+type BooleanNode struct {
+	*Base
+	Key   string
+	Value bool
+}
+
+// OperatorNode represents an operator value like
+// AND, OR, NOT, =, <= ... and so on
+type OperatorNode struct {
+	*Base
+	Value string
+}
+
+// GroupNode represents a collection of many grouped nodes
+type GroupNode struct {
+	*Base
+	Key   string
+	Nodes []Node
+}

services/search/pkg/query/ast/test/test.go

@@ -0,0 +1,26 @@
+// Package test provides shared test primitives for ast testing.
+package test
+
+import (
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+
+	"github.com/owncloud/ocis/v2/services/search/pkg/query/ast"
+)
+
+// DiffAst returns a human-readable report of the differences between two values
+// by default it ignores every ast node Base field.
+func DiffAst(x, y interface{}, opts ...cmp.Option) string {
+	return cmp.Diff(
+		x,
+		y,
+		append(
+			opts,
+			cmpopts.IgnoreFields(ast.Ast{}, "Base"),
+			cmpopts.IgnoreFields(ast.StringNode{}, "Base"),
+			cmpopts.IgnoreFields(ast.OperatorNode{}, "Base"),
+			cmpopts.IgnoreFields(ast.GroupNode{}, "Base"),
+			cmpopts.IgnoreFields(ast.BooleanNode{}, "Base"),
+		)...,
+	)
+}