1 // Copyright 2012 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
5 // Package types declares the data types and implements
6 // the algorithms for type-checking of Go packages. Use
7 // [Config.Check] to invoke the type checker for a package.
8 // Alternatively, create a new type checker with [NewChecker]
9 // and invoke it incrementally by calling [Checker.Files].
11 // Type-checking consists of several interdependent phases:
13 // Name resolution maps each identifier (ast.Ident) in the program to the
14 // language object ([Object]) it denotes.
15 // Use [Info].{Defs,Uses,Implicits} for the results of name resolution.
17 // Constant folding computes the exact constant value (constant.Value)
18 // for every expression (ast.Expr) that is a compile-time constant.
19 // Use Info.Types[expr].Value for the results of constant folding.
21 // [Type] inference computes the type ([Type]) of every expression ([ast.Expr])
22 // and checks for compliance with the language specification.
23 // Use [Info.Types][expr].Type for the results of type inference.
25 // For a tutorial, see https://golang.org/s/types-tutorial.
34 . "internal/types/errors"
37 // An Error describes a type-checking error; it implements the error interface.
38 // A "soft" error is an error that still permits a valid interpretation of a
39 // package (such as "unused variable"); "hard" errors may lead to unpredictable
40 // behavior if ignored.
42 Fset *token.FileSet // file set for interpretation of Pos
43 Pos token.Pos // error position
44 Msg string // error message
45 Soft bool // if set, error is "soft"
47 // go116code is a future API, unexported as the set of error codes is large
48 // and likely to change significantly during experimentation. Tools wishing
49 // to preview this feature may read go116code using reflection (see
50 // errorcodes_test.go), but beware that there is no guarantee of future
57 // Error returns an error string formatted as follows:
58 // filename:line:column: message
59 func (err Error) Error() string {
60 return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg)
63 // An ArgumentError holds an error associated with an argument index.
64 type ArgumentError struct {
69 func (e *ArgumentError) Error() string { return e.Err.Error() }
70 func (e *ArgumentError) Unwrap() error { return e.Err }
72 // An Importer resolves import paths to Packages.
74 // CAUTION: This interface does not support the import of locally
75 // vendored packages. See https://golang.org/s/go15vendor.
76 // If possible, external implementations should implement [ImporterFrom].
77 type Importer interface {
78 // Import returns the imported package for the given import path.
79 // The semantics is like for ImporterFrom.ImportFrom except that
80 // dir and mode are ignored (since they are not present).
81 Import(path string) (*Package, error)
84 // ImportMode is reserved for future use.
87 // An ImporterFrom resolves import paths to packages; it
88 // supports vendoring per https://golang.org/s/go15vendor.
89 // Use go/importer to obtain an ImporterFrom implementation.
90 type ImporterFrom interface {
91 // Importer is present for backward-compatibility. Calling
92 // Import(path) is the same as calling ImportFrom(path, "", 0);
93 // i.e., locally vendored packages may not be found.
94 // The types package does not call Import if an ImporterFrom
98 // ImportFrom returns the imported package for the given import
99 // path when imported by a package file located in dir.
100 // If the import failed, besides returning an error, ImportFrom
101 // is encouraged to cache and return a package anyway, if one
102 // was created. This will reduce package inconsistencies and
103 // follow-on type checker errors due to the missing package.
104 // The mode value must be 0; it is reserved for future use.
105 // Two calls to ImportFrom with the same path and dir must
106 // return the same package.
107 ImportFrom(path, dir string, mode ImportMode) (*Package, error)
110 // A Config specifies the configuration for type checking.
111 // The zero value for Config is a ready-to-use default configuration.
113 // Context is the context used for resolving global identifiers. If nil, the
114 // type checker will initialize this field with a newly created context.
117 // GoVersion describes the accepted Go language version. The string must
118 // start with a prefix of the form "go%d.%d" (e.g. "go1.20", "go1.21rc1", or
119 // "go1.21.0") or it must be empty; an empty string disables Go language
120 // version checks. If the format is invalid, invoking the type checker will
121 // result in an error.
124 // If IgnoreFuncBodies is set, function bodies are not
126 IgnoreFuncBodies bool
128 // If FakeImportC is set, `import "C"` (for packages requiring Cgo)
129 // declares an empty "C" package and errors are omitted for qualified
130 // identifiers referring to package C (which won't find an object).
131 // This feature is intended for the standard library cmd/api tool.
133 // Caution: Effects may be unpredictable due to follow-on errors.
134 // Do not use casually!
137 // If go115UsesCgo is set, the type checker expects the
138 // _cgo_gotypes.go file generated by running cmd/cgo to be
139 // provided as a package source file. Qualified identifiers
140 // referring to package C will be resolved to cgo-provided
141 // declarations within _cgo_gotypes.go.
143 // It is an error to set both FakeImportC and go115UsesCgo.
146 // If _Trace is set, a debug trace is printed to stdout.
149 // If Error != nil, it is called with each error found
150 // during type checking; err has dynamic type Error.
151 // Secondary errors (for instance, to enumerate all types
152 // involved in an invalid recursive type declaration) have
153 // error strings that start with a '\t' character.
154 // If Error == nil, type-checking stops with the first
156 Error func(err error)
158 // An importer is used to import packages referred to from
159 // import declarations.
160 // If the installed importer implements ImporterFrom, the type
161 // checker calls ImportFrom instead of Import.
162 // The type checker reports an error if an importer is needed
163 // but none was installed.
166 // If Sizes != nil, it provides the sizing functions for package unsafe.
167 // Otherwise SizesFor("gc", "amd64") is used instead.
170 // If DisableUnusedImportCheck is set, packages are not checked
171 // for unused imports.
172 DisableUnusedImportCheck bool
174 // If EnableAlias is set, alias declarations produce an _Alias type.
175 // Otherwise the alias information is only in the type name, which
176 // points directly to the actual (aliased) type.
179 // If a non-empty _ErrorURL format string is provided, it is used
180 // to format an error URL link that is appended to the first line
181 // of an error message. ErrorURL must be a format string containing
182 // exactly one "%s" format, e.g. "[go.dev/e/%s]".
186 func srcimporter_setUsesCgo(conf *Config) {
187 conf.go115UsesCgo = true
190 // Info holds result type information for a type-checked package.
191 // Only the information for which a map is provided is collected.
192 // If the package has type errors, the collected information may
195 // Types maps expressions to their types, and for constant
196 // expressions, also their values. Invalid expressions are
199 // For (possibly parenthesized) identifiers denoting built-in
200 // functions, the recorded signatures are call-site specific:
201 // if the call result is not a constant, the recorded type is
202 // an argument-specific signature. Otherwise, the recorded type
205 // The Types map does not record the type of every identifier,
206 // only those that appear where an arbitrary expression is
207 // permitted. For instance, the identifier f in a selector
208 // expression x.f is found only in the Selections map, the
209 // identifier z in a variable declaration 'var z int' is found
210 // only in the Defs map, and identifiers denoting packages in
211 // qualified identifiers are collected in the Uses map.
212 Types map[ast.Expr]TypeAndValue
214 // Instances maps identifiers denoting generic types or functions to their
215 // type arguments and instantiated type.
217 // For example, Instances will map the identifier for 'T' in the type
218 // instantiation T[int, string] to the type arguments [int, string] and
219 // resulting instantiated *Named type. Given a generic function
220 // func F[A any](A), Instances will map the identifier for 'F' in the call
221 // expression F(int(1)) to the inferred type arguments [int], and resulting
222 // instantiated *Signature.
224 // Invariant: Instantiating Uses[id].Type() with Instances[id].TypeArgs
225 // results in an equivalent of Instances[id].Type.
226 Instances map[*ast.Ident]Instance
228 // Defs maps identifiers to the objects they define (including
229 // package names, dots "." of dot-imports, and blank "_" identifiers).
230 // For identifiers that do not denote objects (e.g., the package name
231 // in package clauses, or symbolic variables t in t := x.(type) of
232 // type switch headers), the corresponding objects are nil.
234 // For an embedded field, Defs returns the field *Var it defines.
236 // Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos()
237 Defs map[*ast.Ident]Object
239 // Uses maps identifiers to the objects they denote.
241 // For an embedded field, Uses returns the *TypeName it denotes.
243 // Invariant: Uses[id].Pos() != id.Pos()
244 Uses map[*ast.Ident]Object
246 // Implicits maps nodes to their implicitly declared objects, if any.
247 // The following node and object types may appear:
249 // node declared object
251 // *ast.ImportSpec *PkgName for imports without renames
252 // *ast.CaseClause type-specific *Var for each type switch case clause (incl. default)
253 // *ast.Field anonymous parameter *Var (incl. unnamed results)
255 Implicits map[ast.Node]Object
257 // Selections maps selector expressions (excluding qualified identifiers)
258 // to their corresponding selections.
259 Selections map[*ast.SelectorExpr]*Selection
261 // Scopes maps ast.Nodes to the scopes they define. Package scopes are not
262 // associated with a specific node but with all files belonging to a package.
263 // Thus, the package scope can be found in the type-checked Package object.
264 // Scopes nest, with the Universe scope being the outermost scope, enclosing
265 // the package scope, which contains (one or more) files scopes, which enclose
266 // function scopes which in turn enclose statement and function literal scopes.
267 // Note that even though package-level functions are declared in the package
268 // scope, the function scopes are embedded in the file scope of the file
269 // containing the function declaration.
271 // The following node types may appear in Scopes:
279 // *ast.TypeSwitchStmt
285 Scopes map[ast.Node]*Scope
287 // InitOrder is the list of package-level initializers in the order in which
288 // they must be executed. Initializers referring to variables related by an
289 // initialization dependency appear in topological order, the others appear
290 // in source order. Variables without an initialization expression do not
291 // appear in this list.
292 InitOrder []*Initializer
294 // FileVersions maps a file to its Go version string.
295 // If the file doesn't specify a version, the reported
296 // string is Config.GoVersion.
297 // Version strings begin with “go”, like “go1.21”, and
298 // are suitable for use with the [go/version] package.
299 FileVersions map[*ast.File]string
302 func (info *Info) recordTypes() bool {
303 return info.Types != nil
306 // TypeOf returns the type of expression e, or nil if not found.
307 // Precondition: the Types, Uses and Defs maps are populated.
308 func (info *Info) TypeOf(e ast.Expr) Type {
309 if t, ok := info.Types[e]; ok {
312 if id, _ := e.(*ast.Ident); id != nil {
313 if obj := info.ObjectOf(id); obj != nil {
320 // ObjectOf returns the object denoted by the specified id,
321 // or nil if not found.
323 // If id is an embedded struct field, [Info.ObjectOf] returns the field (*[Var])
324 // it defines, not the type (*[TypeName]) it uses.
326 // Precondition: the Uses and Defs maps are populated.
327 func (info *Info) ObjectOf(id *ast.Ident) Object {
328 if obj := info.Defs[id]; obj != nil {
334 // PkgNameOf returns the local package name defined by the import,
335 // or nil if not found.
337 // For dot-imports, the package name is ".".
339 // Precondition: the Defs and Implicts maps are populated.
340 func (info *Info) PkgNameOf(imp *ast.ImportSpec) *PkgName {
343 obj = info.Defs[imp.Name]
345 obj = info.Implicits[imp]
347 pkgname, _ := obj.(*PkgName)
351 // TypeAndValue reports the type and value (for constants)
352 // of the corresponding expression.
353 type TypeAndValue struct {
359 // IsVoid reports whether the corresponding expression
360 // is a function call without results.
361 func (tv TypeAndValue) IsVoid() bool {
362 return tv.mode == novalue
365 // IsType reports whether the corresponding expression specifies a type.
366 func (tv TypeAndValue) IsType() bool {
367 return tv.mode == typexpr
370 // IsBuiltin reports whether the corresponding expression denotes
371 // a (possibly parenthesized) built-in function.
372 func (tv TypeAndValue) IsBuiltin() bool {
373 return tv.mode == builtin
376 // IsValue reports whether the corresponding expression is a value.
377 // Builtins are not considered values. Constant values have a non-
379 func (tv TypeAndValue) IsValue() bool {
381 case constant_, variable, mapindex, value, commaok, commaerr:
387 // IsNil reports whether the corresponding expression denotes the
388 // predeclared value nil.
389 func (tv TypeAndValue) IsNil() bool {
390 return tv.mode == value && tv.Type == Typ[UntypedNil]
393 // Addressable reports whether the corresponding expression
394 // is addressable (https://golang.org/ref/spec#Address_operators).
395 func (tv TypeAndValue) Addressable() bool {
396 return tv.mode == variable
399 // Assignable reports whether the corresponding expression
400 // is assignable to (provided a value of the right type).
401 func (tv TypeAndValue) Assignable() bool {
402 return tv.mode == variable || tv.mode == mapindex
405 // HasOk reports whether the corresponding expression may be
406 // used on the rhs of a comma-ok assignment.
407 func (tv TypeAndValue) HasOk() bool {
408 return tv.mode == commaok || tv.mode == mapindex
411 // Instance reports the type arguments and instantiated type for type and
412 // function instantiations. For type instantiations, [Type] will be of dynamic
413 // type *[Named]. For function instantiations, [Type] will be of dynamic type
415 type Instance struct {
420 // An Initializer describes a package-level variable, or a list of variables in case
421 // of a multi-valued initialization expression, and the corresponding initialization
423 type Initializer struct {
424 Lhs []*Var // var Lhs = Rhs
428 func (init *Initializer) String() string {
430 for i, lhs := range init.Lhs {
432 buf.WriteString(", ")
434 buf.WriteString(lhs.Name())
436 buf.WriteString(" = ")
437 WriteExpr(&buf, init.Rhs)
441 // Check type-checks a package and returns the resulting package object and
442 // the first error if any. Additionally, if info != nil, Check populates each
443 // of the non-nil maps in the [Info] struct.
445 // The package is marked as complete if no errors occurred, otherwise it is
446 // incomplete. See [Config.Error] for controlling behavior in the presence of
449 // The package is specified by a list of *ast.Files and corresponding
450 // file set, and the package path the package is identified with.
451 // The clean path must not be empty or dot (".").
452 func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, info *Info) (*Package, error) {
453 pkg := NewPackage(path, "")
454 return pkg, NewChecker(conf, fset, pkg, info).Files(files)
457 // AssertableTo reports whether a value of type V can be asserted to have type T.
459 // The behavior of AssertableTo is unspecified in three cases:
460 // - if T is Typ[Invalid]
461 // - if V is a generalized interface; i.e., an interface that may only be used
462 // as a type constraint in Go code
463 // - if T is an uninstantiated generic type
464 func AssertableTo(V *Interface, T Type) bool {
465 // Checker.newAssertableTo suppresses errors for invalid types, so we need special
467 if !isValid(T.Underlying()) {
470 return (*Checker)(nil).newAssertableTo(nopos, V, T, nil)
473 // AssignableTo reports whether a value of type V is assignable to a variable
476 // The behavior of AssignableTo is unspecified if V or T is Typ[Invalid] or an
477 // uninstantiated generic type.
478 func AssignableTo(V, T Type) bool {
479 x := operand{mode: value, typ: V}
480 ok, _ := x.assignableTo(nil, T, nil) // check not needed for non-constant x
484 // ConvertibleTo reports whether a value of type V is convertible to a value of
487 // The behavior of ConvertibleTo is unspecified if V or T is Typ[Invalid] or an
488 // uninstantiated generic type.
489 func ConvertibleTo(V, T Type) bool {
490 x := operand{mode: value, typ: V}
491 return x.convertibleTo(nil, T, nil) // check not needed for non-constant x
494 // Implements reports whether type V implements interface T.
496 // The behavior of Implements is unspecified if V is Typ[Invalid] or an uninstantiated
498 func Implements(V Type, T *Interface) bool {
500 // All types (even Typ[Invalid]) implement the empty interface.
503 // Checker.implements suppresses errors for invalid types, so we need special
505 if !isValid(V.Underlying()) {
508 return (*Checker)(nil).implements(0, V, T, false, nil)
511 // Satisfies reports whether type V satisfies the constraint T.
513 // The behavior of Satisfies is unspecified if V is Typ[Invalid] or an uninstantiated
515 func Satisfies(V Type, T *Interface) bool {
516 return (*Checker)(nil).implements(0, V, T, true, nil)
519 // Identical reports whether x and y are identical types.
520 // Receivers of [Signature] types are ignored.
521 func Identical(x, y Type) bool {
523 return c.identical(x, y, nil)
526 // IdenticalIgnoreTags reports whether x and y are identical types if tags are ignored.
527 // Receivers of [Signature] types are ignored.
528 func IdenticalIgnoreTags(x, y Type) bool {
531 return c.identical(x, y, nil)