php2go

Convert PHP source code to Go by AST walking.

The goal is to produce idiomatic, maintainable Go code as part of a one-off conversion. This is not generally possible for highly dynamic PHP code, that may require manual fixups.

Progress

Phase 1

• Convert some small programs
• Error handling
  • All functions return (type, error)
  • Convert throw to err return
  • Non-leaf function calls need to check + bubble errors
• Array handling
  • Infer whether to use slice/map for PHP array
• [-] Namespaces
  • Basic support for namespace -> package name transformation
  • Resolve namespace names in calls
  • Resolve use statements
• if
• for/foreach
• switch
• Generators
• Goto
• null -> nil
• Consts and define()
  • Magic constants (__LINE__,__FILE__ etc)
  • Predefined constants (PHP_VERSION, PHP_EOL, PHP_OS, PHP_INT_MAX etc)
• isset/unset
• instanceof
• Ternary expressions
  • Implemented as inline closure
• die
• try/catch/finally
  • Implement using err checks, not panic/recover
    • Any statements within the try block should capture the finally/catch to run within any interior err-check blocks
  • finally
    • Runs before any return statement inside the try block or catch block; also runs after the try block is complete
    • Maybe finally would be more concisely implemented as defer inside an IIFE, but that is not idiomatic, maintainable Go code
• Abandon upon sight of highly dynamic constructs
  • eval
  • extract
  • variable-variables
  • Attempts to enable magic_quotes or register_globals
• Detect assignment expressions
  • Go doesn't support assignment in rvalues, only as a statement
  • When walking below stmt level, need to first fully walk and check for any function calls + assignments that may need hoisting (and we can probably only do that correctly if there is no short-circuiting)
  • Add subtree walk + catch error for this case
• Closures
  • Handle value/reference captures
• Convert top-level calls to init()/main()
  • Wrap in function
  • Determine init/main based on package name
• Class/object transformations
  • Convert new X constructor calls to NewX
  • Visibility
    • Apply PHP visibility modifiers as Go case change
    • Call mangled function name at call sites
    • PHP variable names are case-sensitive, function names are case-insensitive
  • Static methods
  • Inheritance partial
  • Interfaces
  • Class constants
  • super
    • Need to track current conversion state through into function generator, to select the concrete parent
  • parent::
  • self::
  • static::
  • Traits / use
  • Abstract methods
• Track golang package imports
• Variadic function parameters
• Preserve comments

Productionize

• Multi-file programs
  • Include/Require
• Infer whether to declare variable (var / :=) or reuse (=)
  • Track current visibility scope
• Comprehensive coverage of all AST node types
  • Create full-coverage interface to implement
  • Node
  • Stmt
  • Expr
  • Assign
  • Binary
  • Scalar
    • Heredocs/nowdocs
• Numbered break/continue
• Type inference
  • Type declarations for literals (string, slice/map with constant initializer, etc)
  • Convert known PHP typenames to Go equivalents
  • Parse extra types from phpdoc blocks
• Hoisting pass for rvalue expressions
  • Preincrement statements
  • Behaviour of function calls in rvalue cases where err cannot be checked
  • Assignment expressions
    • Alternately - we can support the form if foo := bar(); foo {
• Simple standard library transformations
  • common string/array functions
  • More string/array functions
    • Top 100 from https://www.exakat.io/top-100-php-functions/
  • substr -> slice index operator
    • This has the same value semantics for string literals, but not variables all cases
  • error_reporting(E_ALL) --> just remove it
  • ini_set('display_errors', 'On') --> remove it when the parameter is known
• Elide error return for functions that cannot throw
  • ?? Could be a standalone Go refactoring tool

Moonshots

• Extended library/environment transformations
  • Standard library transformations
    • Track golang package imports
    • Handle conflicts between golang stdlib packages / local variable names
    • uasort -> sort.Slice
    • preg -> regexp
    • json -> encoding/json
    • Output buffering (ob_start / ob_get_clean)
      • Can push/pop os.Stdout onto a private stack, then we can keep using fmt.Print
  • PHP Superglobal transformations
    • $_SERVER['argv'] to os.Args
    • $_GET['name'] to r.FormValue('name')
  • Common 3rd party package transformations to popular equivalents (optional)
    • Guzzle
    • AWS SDK
    • PHPUnit -> Go Test
    • Replace Composer/PSR-4 autoloading with Go imports
• Preserve rough line spacing
• Somehow detect whether map use should be order-preserving
• Support scoped namespace (namespace { ... }) and multiple namespaces in file
• Validation on imported comment formats
• Convert wordpress / mediawiki / symfony
  • Option to convert with preset=cli, preset=web, webroot path
  • Option to generate built-in web server
• Generate source maps
  • The parser does have full positional information - exporting at the stmt level would be reasonable
  • But the gofmt pass may lose this information
• Command-line tool option to go run

Reference

• The Go Programming Language Specification