// Copyright 2012 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.
// Package types declares the data types and implements
// the algorithms for type-checking of Go packages. Use
// [Config.Check] to invoke the type checker for a package.
// Alternatively, create a new type checker with [NewChecker]
// and invoke it incrementally by calling [Checker.Files].
//
// Type-checking consists of several interdependent phases:
//
// Name resolution maps each identifier ([ast.Ident]) in the program
// to the symbol ([Object]) it denotes. Use the Defs and Uses fields
// of [Info] or the [Info.ObjectOf] method to find the symbol for an
// identifier, and use the Implicits field of [Info] to find the
// symbol for certain other kinds of syntax node.
//
// Constant folding computes the exact constant value
// ([constant.Value]) of every expression ([ast.Expr]) that is a
// compile-time constant. Use the Types field of [Info] to find the
// results of constant folding for an expression.
//
// Type deduction computes the type ([Type]) of every expression
// ([ast.Expr]) and checks for compliance with the language
// specification. Use the Types field of [Info] for the results of
// type deduction.
//
// Applications that need to type-check one or more complete packages
// of Go source code may find it more convenient not to invoke the
// type checker directly but instead to use the Load function in
// package [golang.org/x/tools/go/packages].
//
// For a tutorial, see https://go.dev/s/types-tutorial.
package types
import (
"bytes"
"fmt"
"go/ast"
"go/constant"
"go/token"
. "internal/types/errors"
_ "unsafe" // for linkname
)
// An Error describes a type-checking error; it implements the error interface.
// A "soft" error is an error that still permits a valid interpretation of a
// package (such as "unused variable"); "hard" errors may lead to unpredictable
// behavior if ignored.
type Error struct {
Fset *token.FileSet // file set for interpretation of Pos
Pos token.Pos // error position
Msg string // error message
Soft bool // if set, error is "soft"
// go116code is a future API, unexported as the set of error codes is large
// and likely to change significantly during experimentation. Tools wishing
// to preview this feature may read go116code using reflection (see
// errorcodes_test.go), but beware that there is no guarantee of future
// compatibility.
go116code Code
go116start token.Pos
go116end token.Pos
}
// Error returns an error string formatted as follows:
// filename:line:column: message
func (err Error) Error() string {
return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg)
}
// An ArgumentError holds an error associated with an argument index.
type ArgumentError struct {
Index int
Err error
}
func (e *ArgumentError) Error() string { return e.Err.Error() }
func (e *ArgumentError) Unwrap() error { return e.Err }
// An Importer resolves import paths to Packages.
//
// CAUTION: This interface does not support the import of locally
// vendored packages. See https://golang.org/s/go15vendor.
// If possible, external implementations should implement [ImporterFrom].
type Importer interface {
// Import returns the imported package for the given import path.
// The semantics is like for ImporterFrom.ImportFrom except that
// dir and mode are ignored (since they are not present).
Import(path string) (*Package, error)
}
// ImportMode is reserved for future use.
type ImportMode int
// An ImporterFrom resolves import paths to packages; it
// supports vendoring per https://golang.org/s/go15vendor.
// Use go/importer to obtain an ImporterFrom implementation.
type ImporterFrom interface {
// Importer is present for backward-compatibility. Calling
// Import(path) is the same as calling ImportFrom(path, "", 0);
// i.e., locally vendored packages may not be found.
// The types package does not call Import if an ImporterFrom
// is present.
Importer
// ImportFrom returns the imported package for the given import
// path when imported by a package file located in dir.
// If the import failed, besides returning an error, ImportFrom
// is encouraged to cache and return a package anyway, if one
// was created. This will reduce package inconsistencies and
// follow-on type checker errors due to the missing package.
// The mode value must be 0; it is reserved for future use.
// Two calls to ImportFrom with the same path and dir must
// return the same package.
ImportFrom(path, dir string, mode ImportMode) (*Package, error)
}
// A Config specifies the configuration for type checking.
// The zero value for Config is a ready-to-use default configuration.
type Config struct {
// Context is the context used for resolving global identifiers. If nil, the
// type checker will initialize this field with a newly created context.
Context *Context
// GoVersion describes the accepted Go language version. The string must
// start with a prefix of the form "go%d.%d" (e.g. "go1.20", "go1.21rc1", or
// "go1.21.0") or it must be empty; an empty string disables Go language
// version checks. If the format is invalid, invoking the type checker will
// result in an error.
GoVersion string
// If IgnoreFuncBodies is set, function bodies are not
// type-checked.
IgnoreFuncBodies bool
// If FakeImportC is set, `import "C"` (for packages requiring Cgo)
// declares an empty "C" package and errors are omitted for qualified
// identifiers referring to package C (which won't find an object).
// This feature is intended for the standard library cmd/api tool.
//
// Caution: Effects may be unpredictable due to follow-on errors.
// Do not use casually!
FakeImportC bool
// If go115UsesCgo is set, the type checker expects the
// _cgo_gotypes.go file generated by running cmd/cgo to be
// provided as a package source file. Qualified identifiers
// referring to package C will be resolved to cgo-provided
// declarations within _cgo_gotypes.go.
//
// It is an error to set both FakeImportC and go115UsesCgo.
go115UsesCgo bool
// If _Trace is set, a debug trace is printed to stdout.
_Trace bool
// If Error != nil, it is called with each error found
// during type checking; err has dynamic type Error.
// Secondary errors (for instance, to enumerate all types
// involved in an invalid recursive type declaration) have
// error strings that start with a '\t' character.
// If Error == nil, type-checking stops with the first
// error found.
Error func(err error)
// An importer is used to import packages referred to from
// import declarations.
// If the installed importer implements ImporterFrom, the type
// checker calls ImportFrom instead of Import.
// The type checker reports an error if an importer is needed
// but none was installed.
Importer Importer
// If Sizes != nil, it provides the sizing functions for package unsafe.
// Otherwise SizesFor("gc", "amd64") is used instead.
Sizes Sizes
// If DisableUnusedImportCheck is set, packages are not checked
// for unused imports.
DisableUnusedImportCheck bool
// If a non-empty _ErrorURL format string is provided, it is used
// to format an error URL link that is appended to the first line
// of an error message. ErrorURL must be a format string containing
// exactly one "%s" format, e.g. "[go.dev/e/%s]".
_ErrorURL string
// If EnableAlias is set, alias declarations produce an Alias type. Otherwise
// the alias information is only in the type name, which points directly to
// the actual (aliased) type.
//
// This setting must not differ among concurrent type-checking operations,
// since it affects the behavior of Universe.Lookup("any").
//
// This flag will eventually be removed (with Go 1.24 at the earliest).
_EnableAlias bool
}
// Linkname for use from srcimporter.
//go:linkname srcimporter_setUsesCgo
func srcimporter_setUsesCgo(conf *Config) {
conf.go115UsesCgo = true
}
// Info holds result type information for a type-checked package.
// Only the information for which a map is provided is collected.
// If the package has type errors, the collected information may
// be incomplete.
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:
// - an identifier f in a selector expression x.f is found
// only in the Selections map;
// - an identifier z in a variable declaration 'var z int'
// is found only in the Defs map;
// - an identifier p denoting a package in a qualified
// identifier p.X is found only in the Uses map.
//
// Similarly, no type is recorded for the (synthetic) FuncType
// node in a FuncDecl.Type field, since there is no corresponding
// syntactic function type expression in the source in this case
// Instead, the function type is found in the Defs map entry for
// the corresponding function declaration.
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
// 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.
//
// In ill-typed code, such as a duplicate declaration of the
// same name, Defs may lack an entry for a declaring identifier.
//
// 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 Scope of a function contains the declarations of any
// type parameters, parameters, and named results, plus any
// local declarations in the body block.
// It is coextensive with the complete extent of the
// function's syntax ([*ast.FuncDecl] or [*ast.FuncLit]).
// The Scopes mapping does not contain an entry for the
// function body ([*ast.BlockStmt]); the function's scope is
// associated with the [*ast.FuncType].
//
// 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
// FileVersions maps a file to its Go version string.
// If the file doesn't specify a version, the reported
// string is Config.GoVersion.
// Version strings begin with “go”, like “go1.21”, and
// are suitable for use with the [go/version] package.
FileVersions map[*ast.File]string
}
func (info *Info) recordTypes() bool {
return info.Types != nil
}
// TypeOf returns the type of expression e, or nil if not found.
// Precondition: the Types, Uses and Defs maps are populated.
func (info *Info) TypeOf(e ast.Expr) Type {
if t, ok := info.Types[e]; ok {
return t.Type
}
if id, _ := e.(*ast.Ident); id != nil {
if obj := info.ObjectOf(id); obj != nil {
return obj.Type()
}
}
return nil
}
// ObjectOf returns the object denoted by the specified id,
// or nil if not found.
//
// If id is an embedded struct field, [Info.ObjectOf] returns the field (*[Var])
// it defines, not the type (*[TypeName]) it uses.
//
// Precondition: the Uses and Defs maps are populated.
func (info *Info) ObjectOf(id *ast.Ident) Object {
if obj := info.Defs[id]; obj != nil {
return obj
}
return info.Uses[id]
}
// PkgNameOf returns the local package name defined by the import,
// or nil if not found.
//
// For dot-imports, the package name is ".".
//
// Precondition: the Defs and Implicts maps are populated.
func (info *Info) PkgNameOf(imp *ast.ImportSpec) *PkgName {
var obj Object
if imp.Name != nil {
obj = info.Defs[imp.Name]
} else {
obj = info.Implicits[imp]
}
pkgname, _ := obj.(*PkgName)
return pkgname
}
// TypeAndValue reports the type and value (for constants)
// of the corresponding expression.
type TypeAndValue struct {
mode operandMode
Type Type
Value constant.Value
}
// IsVoid reports whether the corresponding expression
// is a function call without results.
func (tv TypeAndValue) IsVoid() bool {
return tv.mode == novalue
}
// IsType reports whether the corresponding expression specifies a type.
func (tv TypeAndValue) IsType() bool {
return tv.mode == typexpr
}
// IsBuiltin reports whether the corresponding expression denotes
// a (possibly parenthesized) built-in function.
func (tv TypeAndValue) IsBuiltin() bool {
return tv.mode == builtin
}
// IsValue reports whether the corresponding expression is a value.
// Builtins are not considered values. Constant values have a non-
// nil Value.
func (tv TypeAndValue) IsValue() bool {
switch tv.mode {
case constant_, variable, mapindex, value, commaok, commaerr:
return true
}
return false
}
// IsNil reports whether the corresponding expression denotes the
// predeclared value nil.
func (tv TypeAndValue) IsNil() bool {
return tv.mode == value && tv.Type == Typ[UntypedNil]
}
// Addressable reports whether the corresponding expression
// is addressable (https://golang.org/ref/spec#Address_operators).
func (tv TypeAndValue) Addressable() bool {
return tv.mode == variable
}
// Assignable reports whether the corresponding expression
// is assignable to (provided a value of the right type).
func (tv TypeAndValue) Assignable() bool {
return tv.mode == variable || tv.mode == mapindex
}
// HasOk reports whether the corresponding expression may be
// used on the rhs of a comma-ok assignment.
func (tv TypeAndValue) HasOk() bool {
return tv.mode == commaok || tv.mode == mapindex
}
// Instance reports the type arguments and instantiated type for type and
// function instantiations. For type instantiations, [Type] will be of dynamic
// type *[Named]. For function instantiations, [Type] will be of dynamic type
// *Signature.
type Instance struct {
TypeArgs *TypeList
Type Type
}
// An Initializer describes a package-level variable, or a list of variables in case
// of a multi-valued initialization expression, and the corresponding initialization
// expression.
type Initializer struct {
Lhs []*Var // var Lhs = Rhs
Rhs ast.Expr
}
func (init *Initializer) String() string {
var buf bytes.Buffer
for i, lhs := range init.Lhs {
if i > 0 {
buf.WriteString(", ")
}
buf.WriteString(lhs.Name())
}
buf.WriteString(" = ")
WriteExpr(&buf, init.Rhs)
return buf.String()
}
// Check type-checks a package and returns the resulting package object and
// the first error if any. Additionally, if info != nil, Check populates each
// of the non-nil maps in the [Info] struct.
//
// The package is marked as complete if no errors occurred, otherwise it is
// incomplete. See [Config.Error] for controlling behavior in the presence of
// errors.
//
// The package is specified by a list of *ast.Files and corresponding
// file set, and the package path the package is identified with.
// The clean path must not be empty or dot (".").
func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, info *Info) (*Package, error) {
pkg := NewPackage(path, "")
return pkg, NewChecker(conf, fset, pkg, info).Files(files)
}
