GO Info用法及代码示例

GO语言"go/types"包中"Info"类型的用法及代码示例。

Info 保存type-checked 包的结果类型信息。仅收集为其提供Map的信息。如果包有类型错误，收集的信息可能不完整。

用法:

type Info struct {
    // Types maps expressions to their types, and for constant
    // expressions, also their values.Invalid expressions are
    // omitted.
    //
    // For(possibly parenthesized) identifiers denoting built-in
    // functions, the recorded signatures are call-site specific:
    // if the call result is not a constant, the recorded type is
    // an argument-specific signature.Otherwise, the recorded type
    // is invalid.
    //
    // The Types map does not record the type of every identifier,
    // only those that appear where an arbitrary expression is
    // permitted.For instance, the identifier f in a selector
    // expression x.f is found only in the Selections map, the
    // identifier z in a variable declaration 'var z int' is found
    // only in the Defs map, and identifiers denoting packages in
    // qualified identifiers are collected in the Uses map.
    Types map[ast.Expr]TypeAndValue

    // Instances maps identifiers denoting generic types or functions to their
    // type arguments and instantiated type.
    //
    // For example, Instances will map the identifier for 'T' in the type
    // instantiation T[int, string] to the type arguments [int, string] and
    // resulting instantiated *Named type.Given a generic function
    // func F[A any](A), Instances will map the identifier for 'F' in the call
    // expression F(int(1)) to the inferred type arguments [int], and resulting
    // instantiated *Signature.
    //
    // Invariant: Instantiating Uses[id].Type() with Instances[id].TypeArgs
    // results in an equivalent of Instances[id].Type.
    Instances map[*ast.Ident]Instance // Go 1.18

    // Defs maps identifiers to the objects they define(including
    // package names, dots "." of dot-imports, and blank "_" identifiers).
    // For identifiers that do not denote objects(e.g., the package name
    // in package clauses, or symbolic variables t in t := x.(type) of
    // type switch headers), the corresponding objects are nil.
    //
    // For an embedded field, Defs returns the field *Var it defines.
    //
    // Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos()
    Defs map[*ast.Ident]Object

    // Uses maps identifiers to the objects they denote.
    //
    // For an embedded field, Uses returns the *TypeName it denotes.
    //
    // Invariant: Uses[id].Pos() != id.Pos()
    Uses map[*ast.Ident]Object

    // Implicits maps nodes to their implicitly declared objects, if any.
    // The following node and object types may appear:
    //
    //     node               declared object
    //
    //     *ast.ImportSpec    *PkgName for imports without renames
    //     *ast.CaseClause    type-specific *Var for each type switch case clause(incl.default)
    //     *ast.Field         anonymous parameter *Var(incl.unnamed results)
    //
    Implicits map[ast.Node]Object

    // Selections maps selector expressions(excluding qualified identifiers)
    // to their corresponding selections.
    Selections map[*ast.SelectorExpr]*Selection

    // Scopes maps ast.Nodes to the scopes they define.Package scopes are not
    // associated with a specific node but with all files belonging to a package.
    // Thus, the package scope can be found in the type-checked Package object.
    // Scopes nest, with the Universe scope being the outermost scope, enclosing
    // the package scope, which contains(one or more) files scopes, which enclose
    // function scopes which in turn enclose statement and function literal scopes.
    // Note that even though package-level functions are declared in the package
    // scope, the function scopes are embedded in the file scope of the file
    // containing the function declaration.
    //
    // The following node types may appear in Scopes:
    //
    //     *ast.File
    //     *ast.FuncType
    //     *ast.TypeSpec
    //     *ast.BlockStmt
    //     *ast.IfStmt
    //     *ast.SwitchStmt
    //     *ast.TypeSwitchStmt
    //     *ast.CaseClause
    //     *ast.CommClause
    //     *ast.ForStmt
    //     *ast.RangeStmt
    //
    Scopes map[ast.Node]*Scope

    // InitOrder is the list of package-level initializers in the order in which
    // they must be executed.Initializers referring to variables related by an
    // initialization dependency appear in topological order, the others appear
    // in source order.Variables without an initialization expression do not
    // appear in this list.
    InitOrder []*Initializer
}

package main

import (
	"bytes"
	"fmt"
	"go/ast"
	"go/format"
	"go/parser"
	"go/token"
	"go/types"
	"log"
	"sort"
	"strings"
)

func main() {
	// Parse a single source file.
	const input = `
package fib

type S string

var a, b, c = len(b), S(c), "hello"

func fib(x int) int {
	if x < 2 {
		return x
	}
	return fib(x-1) - fib(x-2)
}`
	fset := token.NewFileSet()
	f, err := parser.ParseFile(fset, "fib.go", input, 0)
	if err != nil {
		log.Fatal(err)
	}

	// Type-check the package.
	// We create an empty map for each kind of input
	// we're interested in, and Check populates them.
	info := types.Info{
		Types: make(map[ast.Expr]types.TypeAndValue),
		Defs:  make(map[*ast.Ident]types.Object),
		Uses:  make(map[*ast.Ident]types.Object),
	}
	var conf types.Config
	pkg, err := conf.Check("fib", fset, []*ast.File{f}, &info)
	if err != nil {
		log.Fatal(err)
	}

	// Print package-level variables in initialization order.
	fmt.Printf("InitOrder: %v\n\n", info.InitOrder)

	// For each named object, print the line and
	// column of its definition and each of its uses.
	fmt.Println("Defs and Uses of each named object:")
	usesByObj := make(map[types.Object][]string)
	for id, obj := range info.Uses {
		posn := fset.Position(id.Pos())
		lineCol := fmt.Sprintf("%d:%d", posn.Line, posn.Column)
		usesByObj[obj] = append(usesByObj[obj], lineCol)
	}
	var items []string
	for obj, uses := range usesByObj {
		sort.Strings(uses)
		item := fmt.Sprintf("%s:\n  defined at %s\n  used at %s",
			types.ObjectString(obj, types.RelativeTo(pkg)),
			fset.Position(obj.Pos()),
			strings.Join(uses, ", "))
		items = append(items, item)
	}
	sort.Strings(items) // sort by line:col, in effect
	fmt.Println(strings.Join(items, "\n"))
	fmt.Println()

	fmt.Println("Types and Values of each expression:")
	items = nil
	for expr, tv := range info.Types {
		var buf bytes.Buffer
		posn := fset.Position(expr.Pos())
		tvstr := tv.Type.String()
		if tv.Value != nil {
			tvstr += " = " + tv.Value.String()
		}
		// line:col | expr | mode : type = value
		fmt.Fprintf(&buf, "%2d:%2d | %-19s | %-7s : %s",
			posn.Line, posn.Column, exprString(fset, expr),
			mode(tv), tvstr)
		items = append(items, buf.String())
	}
	sort.Strings(items)
	fmt.Println(strings.Join(items, "\n"))

}

func mode(tv types.TypeAndValue) string {
	switch {
	case tv.IsVoid():
		return "void"
	case tv.IsType():
		return "type"
	case tv.IsBuiltin():
		return "builtin"
	case tv.IsNil():
		return "nil"
	case tv.Assignable():
		if tv.Addressable() {
			return "var"
		}
		return "mapindex"
	case tv.IsValue():
		return "value"
	default:
		return "unknown"
	}
}

func exprString(fset *token.FileSet, expr ast.Expr) string {
	var buf bytes.Buffer
	format.Node(&buf, fset, expr)
	return buf.String()
}

InitOrder: [c = "hello" b = S(c) a = len(b)]

Defs and Uses of each named object:
builtin len:
  defined at -
  used at 6:15
func fib(x int) int:
  defined at fib.go:8:6
  used at 12:20, 12:9
type S string:
  defined at fib.go:4:6
  used at 6:23
type int:
  defined at -
  used at 8:12, 8:17
type string:
  defined at -
  used at 4:8
var b S:
  defined at fib.go:6:8
  used at 6:19
var c string:
  defined at fib.go:6:11
  used at 6:25
var x int:
  defined at fib.go:8:10
  used at 10:10, 12:13, 12:24, 9:5

Types and Values of each expression:
 4: 8 | string              | type    : string
 6:15 | len                 | builtin : func(fib.S) int
 6:15 | len(b)              | value   : int
 6:19 | b                   | var     : fib.S
 6:23 | S                   | type    : fib.S
 6:23 | S(c)                | value   : fib.S
 6:25 | c                   | var     : string
 6:29 | "hello"             | value   : string = "hello"
 8:12 | int                 | type    : int
 8:17 | int                 | type    : int
 9: 5 | x                   | var     : int
 9: 5 | x < 2               | value   : untyped bool
 9: 9 | 2                   | value   : int = 2
10:10 | x                   | var     : int
12: 9 | fib                 | value   : func(x int) int
12: 9 | fib(x - 1)          | value   : int
12: 9 | fib(x-1) - fib(x-2) | value   : int
12:13 | x                   | var     : int
12:13 | x - 1               | value   : int
12:15 | 1                   | value   : int = 1
12:20 | fib                 | value   : func(x int) int
12:20 | fib(x - 2)          | value   : int
12:24 | x                   | var     : int
12:24 | x - 2               | value   : int
12:26 | 2                   | value   : int = 2