Source: resolve.go in package go/ast

This file implements NewPackage.


package ast

import (
	"fmt"
	"go/scanner"
	"go/token"
	"strconv"
)

type pkgBuilder struct {
	fset   *token.FileSet
	errors scanner.ErrorList
}

func (p *pkgBuilder) error(pos token.Pos, msg string) {
	p.errors.Add(p.fset.Position(pos), msg)
}

func (p *pkgBuilder) errorf(pos token.Pos, format string, args ...interface{}) {
	p.error(pos, fmt.Sprintf(format, args...))
}

func (p *pkgBuilder) declare(scope, altScope *Scope, obj *Object) {
	alt := scope.Insert(obj)

see if there is a conflicting declaration in altScope

		alt = altScope.Lookup(obj.Name)
	}
	if alt != nil {
		prevDecl := ""
		if pos := alt.Pos(); pos.IsValid() {
			prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.fset.Position(pos))
		}
		p.error(obj.Pos(), fmt.Sprintf("%s redeclared in this block%s", obj.Name, prevDecl))
	}
}

func resolve(scope *Scope, ident *Ident) bool {
	for ; scope != nil; scope = scope.Outer {
		if obj := scope.Lookup(ident.Name); obj != nil {
			ident.Obj = obj
			return true
		}
	}
	return false
}

An Importer resolves import paths to package Objects. The imports map records the packages already imported, indexed by package id (canonical import path). An Importer must determine the canonical import path and check the map to see if it is already present in the imports map. If so, the Importer can return the map entry. Otherwise, the Importer should load the package data for the given path into a new *Object (pkg), record pkg in the imports map, and then return pkg.

type Importer func(imports map[string]*Object, path string) (pkg *Object, err error)

NewPackage creates a new Package node from a set of File nodes. It resolves unresolved identifiers across files and updates each file's Unresolved list accordingly. If a non-nil importer and universe scope are provided, they are used to resolve identifiers not declared in any of the package files. Any remaining unresolved identifiers are reported as undeclared. If the files belong to different packages, one package name is selected and files with different package names are reported and then ignored. The result is a package node and a scanner.ErrorList if there were errors.

func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer, universe *Scope) (*Package, error) {
	var p pkgBuilder
	p.fset = fset

complete package scope

	pkgName := ""
	pkgScope := NewScope(universe)

package names must match

		switch name := file.Name.Name; {
		case pkgName == "":
			pkgName = name
		case name != pkgName:
			p.errorf(file.Package, "package %s; expected %s", name, pkgName)
			continue // ignore this file
		}

collect top-level file objects in package scope

		for _, obj := range file.Scope.Objects {
			p.declare(pkgScope, nil, obj)
		}
	}

package global mapping of imported package ids to package objects

	imports := make(map[string]*Object)

complete file scopes with imports and resolve identifiers

ignore file if it belongs to a different package (error has already been reported)

		if file.Name.Name != pkgName {
			continue
		}

build file scope by processing all imports

		importErrors := false
		fileScope := NewScope(pkgScope)
		for _, spec := range file.Imports {
			if importer == nil {
				importErrors = true
				continue
			}
			path, _ := strconv.Unquote(spec.Path.Value)
			pkg, err := importer(imports, path)
			if err != nil {
				p.errorf(spec.Path.Pos(), "could not import %s (%s)", path, err)
				importErrors = true
				continue

TODO(gri) If a local package name != "." is provided, global identifier resolution could proceed even if the import failed. Consider adjusting the logic here a bit.

local name overrides imported package name

			name := pkg.Name
			if spec.Name != nil {
				name = spec.Name.Name
			}

add import to file scope

merge imported scope with file scope

				for _, obj := range pkg.Data.(*Scope).Objects {
					p.declare(fileScope, pkgScope, obj)
				}

declare imported package object in file scope (do not re-use pkg in the file scope but create a new object instead; the Decl field is different for different files)

				obj := NewObj(Pkg, name)
				obj.Decl = spec
				obj.Data = pkg.Data
				p.declare(fileScope, pkgScope, obj)
			}
		}

resolve identifiers

don't use the universe scope without correct imports (objects in the universe may be shadowed by imports; with missing imports, identifiers might get resolved incorrectly to universe objects)

			pkgScope.Outer = nil
		}
		i := 0
		for _, ident := range file.Unresolved {
			if !resolve(fileScope, ident) {
				p.errorf(ident.Pos(), "undeclared name: %s", ident.Name)
				file.Unresolved[i] = ident
				i++
			}

		}
		file.Unresolved = file.Unresolved[0:i]
		pkgScope.Outer = universe // reset universe scope
	}

	p.errors.Sort()
	return &Package{pkgName, pkgScope, imports, files}, p.errors.Err()