src/go/types/api.go - toolchain/go - Git at Google

 // 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
 // language object ([Object]) it denotes.
 // Use [Info].{Defs,Uses,Implicits} for the results of name resolution.
 //
 // Constant folding computes the exact constant value (constant.Value)
 // for every expression (ast.Expr) that is a compile-time constant.
 // Use Info.Types[expr].Value for the results of constant folding.
 //
 // [Type] inference computes the type ([Type]) of every expression ([ast.Expr])
 // and checks for compliance with the language specification.
 // Use [Info.Types][expr].Type for the results of type inference.
 //
 // For a tutorial, see https://golang.org/s/types-tutorial.
 package types

 import (
 	"bytes"
 	"fmt"
 	"go/ast"
 	"go/constant"
 	"go/token"
 	. "internal/types/errors"
 )

 // 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
 }

 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, 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

 	// 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 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)
 }
	// 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
	// language object ([Object]) it denotes.
	// Use [Info].{Defs,Uses,Implicits} for the results of name resolution.
	//
	// Constant folding computes the exact constant value (constant.Value)
	// for every expression (ast.Expr) that is a compile-time constant.
	// Use Info.Types[expr].Value for the results of constant folding.
	//
	// [Type] inference computes the type ([Type]) of every expression ([ast.Expr])
	// and checks for compliance with the language specification.
	// Use [Info.Types][expr].Type for the results of type inference.
	//
	// For a tutorial, see https://golang.org/s/types-tutorial.
	package types

	import (
	"bytes"
	"fmt"
	"go/ast"
	"go/constant"
	"go/token"
	. "internal/types/errors"
	)

	// 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
	}

	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, 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

	// 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 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)
	}