rse/astq: Abstract Syntax Tree (AST) Query Engine

A search axis usually walks along the references between nodes (at least in case of ASTy based AST). But in case the underlying AST and its adapter uses typed references, you can optionally constrain the search axis to take only references matching the type id into account.

axis ::= axis-direction axis-type? axis-direction ::= axis-child | axis-sibling-left | axis-sibling-right | axis-sibling | axis-parent | axis-preceding | axis-following axis-child ::= ("/" | "//" | "./" | ".//") axis-sibling-left ::= ("-/" | "-//") axis-sibling-right ::= ("+/" | "+//") axis-sibling ::= ("~/" | "~//") axis-parent ::= ("../" | "..//") axis-preceding ::= "//" axis-type ::= ":" (id | string) result ::= "!" match ::= id | string | "*" filter ::= "[" expr "]"

The real power comes through the optional filter expression: it can be applied to each query step and it recursively(!) can contain sub-queries with the help of embedded query paths! An illustrating combined example is:

// Foo / Bar [ / Baz [ @bar == 'baz' ] && / Quux ], // Foo2 +---------------------------------------------------------+ query +------------------------------------------------+ +-----+ path +---------------------+ +-----+ path +----+ +-----------------------------------------+ +-----+ step ++ + + + ++ axis +-+ +-+ +-+ +--+ +--+ match +-----------------------------------+ filter +-------------------------------+ expr +---------------+ filter +----------+ expr

The result of a query is always all nodes which match against the last query step of any path (in case of no result marker on any step in the path) or all nodes of matched steps with a result marker. The queries in filter expressions just lead to a boolean decision for the filter, but never cause any resulting nodes theirself.

An expression can be either a ternary/binary conditional expression, logical expression, bitwise expression, relational expression, arithmethical expression, functional call, attribute reference, query parameter, literal value, parenthesis expression or path of a sub-query.

expr ::= conditional | logical | bitwise | relational | arithmentical | function-call | attribute-ref | query-parameter | literal | parenthesis | sub-query conditional ::= expr "?" expr ":" expr | expr "?:" expr logical ::= expr ("&&" | "||") expr | "!" expr bitwise ::= expr ("&" | "|" | "<<" | ">>") expr | "~" expr relational ::= expr ("==" | "!=" | "<=" | ">=" | "<" | ">" | "=~" | "!~") expr arithmethical ::= expr ("+" | "-" | "" | "/" | "%" | "*") expr function-call ::= id "(" (expr ("," expr)*)? ")" attribute-ref ::= "@" (id | string) query-parameter ::= "{" id "}" id ::= /[a-zA-Z_][a-zA-Z0-9_-]*/ literal ::= string | regexp | number | value string ::= /"(\\"|.)"/ | /'(\\'|.)'/ regexp ::= /(\\|.)*/ number ::= /\d+(\.\d+)?$/ value ::= "true" | "false" | "null" | "NaN" | "undefined" parenthesis ::= "(" expr ")" sub-query ::= path // <-- ESSENTIAL RECURSION !!

Notice that the function call parameters can be full expressions theirself, including (through the recursion over sub-query above) full query paths. The available pre-defined standard functions are:

• type(): String:


• attrs(sep: String): String:


• depth(): Number:


• pos(): Number:


• nth(pos: Number): Boolean:


• first(): Boolean:


• last(): Boolean:


• count(array: Object[]): Number:


• below(node: Node): Boolean:


• follows(node: Node): Boolean:


• in(nodes: Node[]): Number:


• substr(str: String, pos: Number, len: Number): String:


• index(str: String, sub: String, pos: Number): Number:


• trim(str: String): String:


• lc(str: String): String:


• uc(str: String): String:


The ASTq API, here assumed to be exposed through the variable ASTQ, provides the following methods (in a notation somewhat resembling TypeScript type definitions):

• new ASTQ(): ASTQ:


• ASTQ#adapter(adapter: (ASTQAdapter | ASTQAdapter[]), force: Boolean): ASTQ:


• ASTQ#version(): { major: Number, minor: Number, micro: Number, date: Number }:


• ASTQ#func(name: String, func: (adapter: Adapter, node: Object, [...]) => Any): ASTQ:


• ASTQ#cache(num: Number): ASTQ:


• ASTQ#compile(selector: String, trace?: Boolean): ASTQQuery {

• ASTQ#execute(node: Object, query: ASTQQuery, params?: Object, trace?: Boolean): Object[]:
  

• ASTQ#query(node: Object, selector: String, params?: Object, trace?: Boolean): Object[]:
  

ASTQAdapter API

For accessing arbitrary AST-style data structures, an adapter has to be provided. By default ASTq has adapters for use with ASTy, XML DOM, Parse5, Cheerio, UniST, JSON and Mozilla AST. The ASTQAdapter interface is:

• ASTQAdapter#taste(node: Object): Boolean:
  

• ASTQAdapter#getParentNode(node: Object): Object:
  

• ASTQAdapter#getChildNodes(node: Object): Object[]:
  

• ASTQAdapter#getNodeType(node: Object): String:
  

• ASTQAdapter#getNodeAttrNames(node: Object): String[]:
  

• ASTQAdapter#getNodeAttrValue(node: Object, attr: String): Any:
  

Example -------

$ cat sample.js
const acorn = require("acorn")
const ASTQ  = require("astq")
let source = 
    class Foo {
        foo () {
            const bar = "quux"
            let baz = 42
        }
    }

let ast = acorn.parse(source, { ecmaVersion: 6 })
let astq = new ASTQ()
astq.adapter("mozast")
astq.query(ast, 
    // VariableDeclarator [
           /:id   Identifier [ @name  ]
        && /:init Literal    [ @value ]
    ]
).forEach(function (node) {
    console.log(${node.id.name}: ${node.init.value})
})
$ babel-node sample.js
bar: quux
baz: 42

Implementation Notice ---------------------

Although ASTq is written in ECMAScript 2018, it is transpiled to older environments and this way runs in really all current (as of 2018) JavaScript environments, of course.

Additionally, there are two transpilation results: first, there is a compressed astq.browser.js for Browser environments. Second, there is an uncompressed astq.node.js for Node.js environments.

The Browser variant astq.browser.js has all external dependencies asty, pegjs-otf, pegjs-util, and cache-lru directly embedded. The Node.js variant astq.node.js still requires the external dependencies asty, pegjs-otf, pegjs-util, and cache-lru.

License -------

Copyright © 2014-2024 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.