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Source file src/go/types/check.go

Documentation: go/types

  // Copyright 2011 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  // This file implements the Check function, which drives type-checking.
  
  package types
  
  import (
  	"go/ast"
  	"go/constant"
  	"go/token"
  )
  
  // debugging/development support
  const (
  	debug = false // leave on during development
  	trace = false // turn on for detailed type resolution traces
  )
  
  // If Strict is set, the type-checker enforces additional
  // rules not specified by the Go 1 spec, but which will
  // catch guaranteed run-time errors if the respective
  // code is executed. In other words, programs passing in
  // Strict mode are Go 1 compliant, but not all Go 1 programs
  // will pass in Strict mode. The additional rules are:
  //
  // - A type assertion x.(T) where T is an interface type
  //   is invalid if any (statically known) method that exists
  //   for both x and T have different signatures.
  //
  const strict = false
  
  // exprInfo stores information about an untyped expression.
  type exprInfo struct {
  	isLhs bool // expression is lhs operand of a shift with delayed type-check
  	mode  operandMode
  	typ   *Basic
  	val   constant.Value // constant value; or nil (if not a constant)
  }
  
  // funcInfo stores the information required for type-checking a function.
  type funcInfo struct {
  	name string    // for debugging/tracing only
  	decl *declInfo // for cycle detection
  	sig  *Signature
  	body *ast.BlockStmt
  }
  
  // A context represents the context within which an object is type-checked.
  type context struct {
  	decl          *declInfo      // package-level declaration whose init expression/function body is checked
  	scope         *Scope         // top-most scope for lookups
  	iota          constant.Value // value of iota in a constant declaration; nil otherwise
  	sig           *Signature     // function signature if inside a function; nil otherwise
  	hasLabel      bool           // set if a function makes use of labels (only ~1% of functions); unused outside functions
  	hasCallOrRecv bool           // set if an expression contains a function call or channel receive operation
  }
  
  // An importKey identifies an imported package by import path and source directory
  // (directory containing the file containing the import). In practice, the directory
  // may always be the same, or may not matter. Given an (import path, directory), an
  // importer must always return the same package (but given two different import paths,
  // an importer may still return the same package by mapping them to the same package
  // paths).
  type importKey struct {
  	path, dir string
  }
  
  // A Checker maintains the state of the type checker.
  // It must be created with NewChecker.
  type Checker struct {
  	// package information
  	// (initialized by NewChecker, valid for the life-time of checker)
  	conf *Config
  	fset *token.FileSet
  	pkg  *Package
  	*Info
  	objMap map[Object]*declInfo   // maps package-level object to declaration info
  	impMap map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
  
  	// information collected during type-checking of a set of package files
  	// (initialized by Files, valid only for the duration of check.Files;
  	// maps and lists are allocated on demand)
  	files            []*ast.File                       // package files
  	unusedDotImports map[*Scope]map[*Package]token.Pos // positions of unused dot-imported packages for each file scope
  
  	firstErr error                 // first error encountered
  	methods  map[string][]*Func    // maps type names to associated methods
  	untyped  map[ast.Expr]exprInfo // map of expressions without final type
  	funcs    []funcInfo            // list of functions to type-check
  	delayed  []func()              // delayed checks requiring fully setup types
  
  	// context within which the current object is type-checked
  	// (valid only for the duration of type-checking a specific object)
  	context
  	pos token.Pos // if valid, identifiers are looked up as if at position pos (used by Eval)
  
  	// debugging
  	indent int // indentation for tracing
  }
  
  // addUnusedImport adds the position of a dot-imported package
  // pkg to the map of dot imports for the given file scope.
  func (check *Checker) addUnusedDotImport(scope *Scope, pkg *Package, pos token.Pos) {
  	mm := check.unusedDotImports
  	if mm == nil {
  		mm = make(map[*Scope]map[*Package]token.Pos)
  		check.unusedDotImports = mm
  	}
  	m := mm[scope]
  	if m == nil {
  		m = make(map[*Package]token.Pos)
  		mm[scope] = m
  	}
  	m[pkg] = pos
  }
  
  // addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
  func (check *Checker) addDeclDep(to Object) {
  	from := check.decl
  	if from == nil {
  		return // not in a package-level init expression
  	}
  	if _, found := check.objMap[to]; !found {
  		return // to is not a package-level object
  	}
  	from.addDep(to)
  }
  
  func (check *Checker) assocMethod(tname string, meth *Func) {
  	m := check.methods
  	if m == nil {
  		m = make(map[string][]*Func)
  		check.methods = m
  	}
  	m[tname] = append(m[tname], meth)
  }
  
  func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
  	m := check.untyped
  	if m == nil {
  		m = make(map[ast.Expr]exprInfo)
  		check.untyped = m
  	}
  	m[e] = exprInfo{lhs, mode, typ, val}
  }
  
  func (check *Checker) later(name string, decl *declInfo, sig *Signature, body *ast.BlockStmt) {
  	check.funcs = append(check.funcs, funcInfo{name, decl, sig, body})
  }
  
  func (check *Checker) delay(f func()) {
  	check.delayed = append(check.delayed, f)
  }
  
  // NewChecker returns a new Checker instance for a given package.
  // Package files may be added incrementally via checker.Files.
  func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
  	// make sure we have a configuration
  	if conf == nil {
  		conf = new(Config)
  	}
  
  	// make sure we have an info struct
  	if info == nil {
  		info = new(Info)
  	}
  
  	return &Checker{
  		conf:   conf,
  		fset:   fset,
  		pkg:    pkg,
  		Info:   info,
  		objMap: make(map[Object]*declInfo),
  		impMap: make(map[importKey]*Package),
  	}
  }
  
  // initFiles initializes the files-specific portion of checker.
  // The provided files must all belong to the same package.
  func (check *Checker) initFiles(files []*ast.File) {
  	// start with a clean slate (check.Files may be called multiple times)
  	check.files = nil
  	check.unusedDotImports = nil
  
  	check.firstErr = nil
  	check.methods = nil
  	check.untyped = nil
  	check.funcs = nil
  	check.delayed = nil
  
  	// determine package name and collect valid files
  	pkg := check.pkg
  	for _, file := range files {
  		switch name := file.Name.Name; pkg.name {
  		case "":
  			if name != "_" {
  				pkg.name = name
  			} else {
  				check.errorf(file.Name.Pos(), "invalid package name _")
  			}
  			fallthrough
  
  		case name:
  			check.files = append(check.files, file)
  
  		default:
  			check.errorf(file.Package, "package %s; expected %s", name, pkg.name)
  			// ignore this file
  		}
  	}
  }
  
  // A bailout panic is used for early termination.
  type bailout struct{}
  
  func (check *Checker) handleBailout(err *error) {
  	switch p := recover().(type) {
  	case nil, bailout:
  		// normal return or early exit
  		*err = check.firstErr
  	default:
  		// re-panic
  		panic(p)
  	}
  }
  
  // Files checks the provided files as part of the checker's package.
  func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
  
  func (check *Checker) checkFiles(files []*ast.File) (err error) {
  	defer check.handleBailout(&err)
  
  	check.initFiles(files)
  
  	check.collectObjects()
  
  	check.packageObjects(check.resolveOrder())
  
  	check.functionBodies()
  
  	check.initOrder()
  
  	if !check.conf.DisableUnusedImportCheck {
  		check.unusedImports()
  	}
  
  	// perform delayed checks
  	for _, f := range check.delayed {
  		f()
  	}
  
  	check.recordUntyped()
  
  	check.pkg.complete = true
  	return
  }
  
  func (check *Checker) recordUntyped() {
  	if !debug && check.Types == nil {
  		return // nothing to do
  	}
  
  	for x, info := range check.untyped {
  		if debug && isTyped(info.typ) {
  			check.dump("%s: %s (type %s) is typed", x.Pos(), x, info.typ)
  			unreachable()
  		}
  		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
  	}
  }
  
  func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
  	assert(x != nil)
  	assert(typ != nil)
  	if mode == invalid {
  		return // omit
  	}
  	assert(typ != nil)
  	if mode == constant_ {
  		assert(val != nil)
  		assert(typ == Typ[Invalid] || isConstType(typ))
  	}
  	if m := check.Types; m != nil {
  		m[x] = TypeAndValue{mode, typ, val}
  	}
  }
  
  func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
  	// f must be a (possibly parenthesized) identifier denoting a built-in
  	// (built-ins in package unsafe always produce a constant result and
  	// we don't record their signatures, so we don't see qualified idents
  	// here): record the signature for f and possible children.
  	for {
  		check.recordTypeAndValue(f, builtin, sig, nil)
  		switch p := f.(type) {
  		case *ast.Ident:
  			return // we're done
  		case *ast.ParenExpr:
  			f = p.X
  		default:
  			unreachable()
  		}
  	}
  }
  
  func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
  	assert(x != nil)
  	if a[0] == nil || a[1] == nil {
  		return
  	}
  	assert(isTyped(a[0]) && isTyped(a[1]) && isBoolean(a[1]))
  	if m := check.Types; m != nil {
  		for {
  			tv := m[x]
  			assert(tv.Type != nil) // should have been recorded already
  			pos := x.Pos()
  			tv.Type = NewTuple(
  				NewVar(pos, check.pkg, "", a[0]),
  				NewVar(pos, check.pkg, "", a[1]),
  			)
  			m[x] = tv
  			// if x is a parenthesized expression (p.X), update p.X
  			p, _ := x.(*ast.ParenExpr)
  			if p == nil {
  				break
  			}
  			x = p.X
  		}
  	}
  }
  
  func (check *Checker) recordDef(id *ast.Ident, obj Object) {
  	assert(id != nil)
  	if m := check.Defs; m != nil {
  		m[id] = obj
  	}
  }
  
  func (check *Checker) recordUse(id *ast.Ident, obj Object) {
  	assert(id != nil)
  	assert(obj != nil)
  	if m := check.Uses; m != nil {
  		m[id] = obj
  	}
  }
  
  func (check *Checker) recordImplicit(node ast.Node, obj Object) {
  	assert(node != nil)
  	assert(obj != nil)
  	if m := check.Implicits; m != nil {
  		m[node] = obj
  	}
  }
  
  func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
  	assert(obj != nil && (recv == nil || len(index) > 0))
  	check.recordUse(x.Sel, obj)
  	if m := check.Selections; m != nil {
  		m[x] = &Selection{kind, recv, obj, index, indirect}
  	}
  }
  
  func (check *Checker) recordScope(node ast.Node, scope *Scope) {
  	assert(node != nil)
  	assert(scope != nil)
  	if m := check.Scopes; m != nil {
  		m[node] = scope
  	}
  }
  

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