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.
4 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].
10 //
11 // Type-checking consists of several interdependent phases:
12 //
13 // Name resolution maps each identifier ([ast.Ident]) in the program
14 // to the symbol ([Object]) it denotes. Use the Defs and Uses fields
15 // of [Info] or the [Info.ObjectOf] method to find the symbol for an
16 // identifier, and use the Implicits field of [Info] to find the
17 // symbol for certain other kinds of syntax node.
18 //
19 // Constant folding computes the exact constant value
20 // ([constant.Value]) of every expression ([ast.Expr]) that is a
21 // compile-time constant. Use the Types field of [Info] to find the
22 // results of constant folding for an expression.
23 //
24 // Type deduction computes the type ([Type]) of every expression
25 // ([ast.Expr]) and checks for compliance with the language
26 // specification. Use the Types field of [Info] for the results of
27 // type deduction.
28 //
29 // Applications that need to type-check one or more complete packages
30 // of Go source code may find it more convenient not to invoke the
31 // type checker directly but instead to use the Load function in
32 // package [golang.org/x/tools/go/packages].
33 //
34 // For a tutorial, see https://go.dev/s/types-tutorial.
35 package types
36 37 import (
38 "bytes"
39 "fmt"
40 "go/ast"
41 "go/constant"
42 "go/token"
43 . "internal/types/errors"
44 _ "unsafe" // for linkname
45 )
46 47 // An Error describes a type-checking error; it implements the error interface.
48 // A "soft" error is an error that still permits a valid interpretation of a
49 // package (such as "unused variable"); "hard" errors may lead to unpredictable
50 // behavior if ignored.
51 type Error struct {
52 Fset *token.FileSet // file set for interpretation of Pos
53 Pos token.Pos // error position
54 Msg string // error message
55 Soft bool // if set, error is "soft"
56 57 // go116code is a future API, unexported as the set of error codes is large
58 // and likely to change significantly during experimentation. Tools wishing
59 // to preview this feature may read go116code using reflection (see
60 // errorcodes_test.go), but beware that there is no guarantee of future
61 // compatibility.
62 go116code Code
63 go116start token.Pos
64 go116end token.Pos
65 }
66 67 // Error returns an error string formatted as follows:
68 // filename:line:column: message
69 func (err Error) Error() string {
70 return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg)
71 }
72 73 // An ArgumentError holds an error associated with an argument index.
74 type ArgumentError struct {
75 Index int
76 Err error
77 }
78 79 func (e *ArgumentError) Error() string { return e.Err.Error() }
80 func (e *ArgumentError) Unwrap() error { return e.Err }
81 82 // An Importer resolves import paths to Packages.
83 //
84 // CAUTION: This interface does not support the import of locally
85 // vendored packages. See https://golang.org/s/go15vendor.
86 // If possible, external implementations should implement [ImporterFrom].
87 type Importer interface {
88 // Import returns the imported package for the given import path.
89 // The semantics is like for ImporterFrom.ImportFrom except that
90 // dir and mode are ignored (since they are not present).
91 Import(path string) (*Package, error)
92 }
93 94 // ImportMode is reserved for future use.
95 type ImportMode int
96 97 // An ImporterFrom resolves import paths to packages; it
98 // supports vendoring per https://golang.org/s/go15vendor.
99 // Use go/importer to obtain an ImporterFrom implementation.
100 type ImporterFrom interface {
101 // Importer is present for backward-compatibility. Calling
102 // Import(path) is the same as calling ImportFrom(path, "", 0);
103 // i.e., locally vendored packages may not be found.
104 // The types package does not call Import if an ImporterFrom
105 // is present.
106 Importer
107 108 // ImportFrom returns the imported package for the given import
109 // path when imported by a package file located in dir.
110 // If the import failed, besides returning an error, ImportFrom
111 // is encouraged to cache and return a package anyway, if one
112 // was created. This will reduce package inconsistencies and
113 // follow-on type checker errors due to the missing package.
114 // The mode value must be 0; it is reserved for future use.
115 // Two calls to ImportFrom with the same path and dir must
116 // return the same package.
117 ImportFrom(path, dir string, mode ImportMode) (*Package, error)
118 }
119 120 // A Config specifies the configuration for type checking.
121 // The zero value for Config is a ready-to-use default configuration.
122 type Config struct {
123 // Context is the context used for resolving global identifiers. If nil, the
124 // type checker will initialize this field with a newly created context.
125 Context *Context
126 127 // GoVersion describes the accepted Go language version. The string must
128 // start with a prefix of the form "go%d.%d" (e.g. "go1.20", "go1.21rc1", or
129 // "go1.21.0") or it must be empty; an empty string disables Go language
130 // version checks. If the format is invalid, invoking the type checker will
131 // result in an error.
132 GoVersion string
133 134 // If IgnoreFuncBodies is set, function bodies are not
135 // type-checked.
136 IgnoreFuncBodies bool
137 138 // If FakeImportC is set, `import "C"` (for packages requiring Cgo)
139 // declares an empty "C" package and errors are omitted for qualified
140 // identifiers referring to package C (which won't find an object).
141 // This feature is intended for the standard library cmd/api tool.
142 //
143 // Caution: Effects may be unpredictable due to follow-on errors.
144 // Do not use casually!
145 FakeImportC bool
146 147 // If go115UsesCgo is set, the type checker expects the
148 // _cgo_gotypes.go file generated by running cmd/cgo to be
149 // provided as a package source file. Qualified identifiers
150 // referring to package C will be resolved to cgo-provided
151 // declarations within _cgo_gotypes.go.
152 //
153 // It is an error to set both FakeImportC and go115UsesCgo.
154 go115UsesCgo bool
155 156 // If _Trace is set, a debug trace is printed to stdout.
157 _Trace bool
158 159 // If Error != nil, it is called with each error found
160 // during type checking; err has dynamic type Error.
161 // Secondary errors (for instance, to enumerate all types
162 // involved in an invalid recursive type declaration) have
163 // error strings that start with a '\t' character.
164 // If Error == nil, type-checking stops with the first
165 // error found.
166 Error func(err error)
167 168 // An importer is used to import packages referred to from
169 // import declarations.
170 // If the installed importer implements ImporterFrom, the type
171 // checker calls ImportFrom instead of Import.
172 // The type checker reports an error if an importer is needed
173 // but none was installed.
174 Importer Importer
175 176 // If Sizes != nil, it provides the sizing functions for package unsafe.
177 // Otherwise SizesFor("gc", "amd64") is used instead.
178 Sizes Sizes
179 180 // If DisableUnusedImportCheck is set, packages are not checked
181 // for unused imports.
182 DisableUnusedImportCheck bool
183 184 // If a non-empty _ErrorURL format string is provided, it is used
185 // to format an error URL link that is appended to the first line
186 // of an error message. ErrorURL must be a format string containing
187 // exactly one "%s" format, e.g. "[go.dev/e/%s]".
188 _ErrorURL string
189 190 // If EnableAlias is set, alias declarations produce an Alias type. Otherwise
191 // the alias information is only in the type name, which points directly to
192 // the actual (aliased) type.
193 //
194 // This setting must not differ among concurrent type-checking operations,
195 // since it affects the behavior of Universe.Lookup("any").
196 //
197 // This flag will eventually be removed (with Go 1.24 at the earliest).
198 _EnableAlias bool
199 }
200 201 // Linkname for use from srcimporter.
202 //go:linkname srcimporter_setUsesCgo
203 204 func srcimporter_setUsesCgo(conf *Config) {
205 conf.go115UsesCgo = true
206 }
207 208 // Info holds result type information for a type-checked package.
209 // Only the information for which a map is provided is collected.
210 // If the package has type errors, the collected information may
211 // be incomplete.
212 type Info struct {
213 // Types maps expressions to their types, and for constant
214 // expressions, also their values. Invalid expressions are
215 // omitted.
216 //
217 // For (possibly parenthesized) identifiers denoting built-in
218 // functions, the recorded signatures are call-site specific:
219 // if the call result is not a constant, the recorded type is
220 // an argument-specific signature. Otherwise, the recorded type
221 // is invalid.
222 //
223 // The Types map does not record the type of every identifier,
224 // only those that appear where an arbitrary expression is
225 // permitted. For instance:
226 // - an identifier f in a selector expression x.f is found
227 // only in the Selections map;
228 // - an identifier z in a variable declaration 'var z int'
229 // is found only in the Defs map;
230 // - an identifier p denoting a package in a qualified
231 // identifier p.X is found only in the Uses map.
232 //
233 // Similarly, no type is recorded for the (synthetic) FuncType
234 // node in a FuncDecl.Type field, since there is no corresponding
235 // syntactic function type expression in the source in this case
236 // Instead, the function type is found in the Defs map entry for
237 // the corresponding function declaration.
238 Types map[ast.Expr]TypeAndValue
239 240 // Instances maps identifiers denoting generic types or functions to their
241 // type arguments and instantiated type.
242 //
243 // For example, Instances will map the identifier for 'T' in the type
244 // instantiation T[int, string] to the type arguments [int, string] and
245 // resulting instantiated *Named type. Given a generic function
246 // func F[A any](A), Instances will map the identifier for 'F' in the call
247 // expression F(int(1)) to the inferred type arguments [int], and resulting
248 // instantiated *Signature.
249 //
250 // Invariant: Instantiating Uses[id].Type() with Instances[id].TypeArgs
251 // results in an equivalent of Instances[id].Type.
252 Instances map[*ast.Ident]Instance
253 254 // Defs maps identifiers to the objects they define (including
255 // package names, dots "." of dot-imports, and blank "_" identifiers).
256 // For identifiers that do not denote objects (e.g., the package name
257 // in package clauses, or symbolic variables t in t := x.(type) of
258 // type switch headers), the corresponding objects are nil.
259 //
260 // For an embedded field, Defs returns the field *Var it defines.
261 //
262 // In ill-typed code, such as a duplicate declaration of the
263 // same name, Defs may lack an entry for a declaring identifier.
264 //
265 // Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos()
266 Defs map[*ast.Ident]Object
267 268 // Uses maps identifiers to the objects they denote.
269 //
270 // For an embedded field, Uses returns the *TypeName it denotes.
271 //
272 // Invariant: Uses[id].Pos() != id.Pos()
273 Uses map[*ast.Ident]Object
274 275 // Implicits maps nodes to their implicitly declared objects, if any.
276 // The following node and object types may appear:
277 //
278 // node declared object
279 //
280 // *ast.ImportSpec *PkgName for imports without renames
281 // *ast.CaseClause type-specific *Var for each type switch case clause (incl. default)
282 // *ast.Field anonymous parameter *Var (incl. unnamed results)
283 //
284 Implicits map[ast.Node]Object
285 286 // Selections maps selector expressions (excluding qualified identifiers)
287 // to their corresponding selections.
288 Selections map[*ast.SelectorExpr]*Selection
289 290 // Scopes maps ast.Nodes to the scopes they define. Package scopes are not
291 // associated with a specific node but with all files belonging to a package.
292 // Thus, the package scope can be found in the type-checked Package object.
293 // Scopes nest, with the Universe scope being the outermost scope, enclosing
294 // the package scope, which contains (one or more) files scopes, which enclose
295 // function scopes which in turn enclose statement and function literal scopes.
296 // Note that even though package-level functions are declared in the package
297 // scope, the function scopes are embedded in the file scope of the file
298 // containing the function declaration.
299 //
300 // The Scope of a function contains the declarations of any
301 // type parameters, parameters, and named results, plus any
302 // local declarations in the body block.
303 // It is coextensive with the complete extent of the
304 // function's syntax ([*ast.FuncDecl] or [*ast.FuncLit]).
305 // The Scopes mapping does not contain an entry for the
306 // function body ([*ast.BlockStmt]); the function's scope is
307 // associated with the [*ast.FuncType].
308 //
309 // The following node types may appear in Scopes:
310 //
311 // *ast.File
312 // *ast.FuncType
313 // *ast.TypeSpec
314 // *ast.BlockStmt
315 // *ast.IfStmt
316 // *ast.SwitchStmt
317 // *ast.TypeSwitchStmt
318 // *ast.CaseClause
319 // *ast.CommClause
320 // *ast.ForStmt
321 // *ast.RangeStmt
322 //
323 Scopes map[ast.Node]*Scope
324 325 // InitOrder is the list of package-level initializers in the order in which
326 // they must be executed. Initializers referring to variables related by an
327 // initialization dependency appear in topological order, the others appear
328 // in source order. Variables without an initialization expression do not
329 // appear in this list.
330 InitOrder []*Initializer
331 332 // FileVersions maps a file to its Go version string.
333 // If the file doesn't specify a version, the reported
334 // string is Config.GoVersion.
335 // Version strings begin with “go”, like “go1.21”, and
336 // are suitable for use with the [go/version] package.
337 FileVersions map[*ast.File]string
338 }
339 340 func (info *Info) recordTypes() bool {
341 return info.Types != nil
342 }
343 344 // TypeOf returns the type of expression e, or nil if not found.
345 // Precondition: the Types, Uses and Defs maps are populated.
346 func (info *Info) TypeOf(e ast.Expr) Type {
347 if t, ok := info.Types[e]; ok {
348 return t.Type
349 }
350 if id, _ := e.(*ast.Ident); id != nil {
351 if obj := info.ObjectOf(id); obj != nil {
352 return obj.Type()
353 }
354 }
355 return nil
356 }
357 358 // ObjectOf returns the object denoted by the specified id,
359 // or nil if not found.
360 //
361 // If id is an embedded struct field, [Info.ObjectOf] returns the field (*[Var])
362 // it defines, not the type (*[TypeName]) it uses.
363 //
364 // Precondition: the Uses and Defs maps are populated.
365 func (info *Info) ObjectOf(id *ast.Ident) Object {
366 if obj := info.Defs[id]; obj != nil {
367 return obj
368 }
369 return info.Uses[id]
370 }
371 372 // PkgNameOf returns the local package name defined by the import,
373 // or nil if not found.
374 //
375 // For dot-imports, the package name is ".".
376 //
377 // Precondition: the Defs and Implicts maps are populated.
378 func (info *Info) PkgNameOf(imp *ast.ImportSpec) *PkgName {
379 var obj Object
380 if imp.Name != nil {
381 obj = info.Defs[imp.Name]
382 } else {
383 obj = info.Implicits[imp]
384 }
385 pkgname, _ := obj.(*PkgName)
386 return pkgname
387 }
388 389 // TypeAndValue reports the type and value (for constants)
390 // of the corresponding expression.
391 type TypeAndValue struct {
392 mode operandMode
393 Type Type
394 Value constant.Value
395 }
396 397 // IsVoid reports whether the corresponding expression
398 // is a function call without results.
399 func (tv TypeAndValue) IsVoid() bool {
400 return tv.mode == novalue
401 }
402 403 // IsType reports whether the corresponding expression specifies a type.
404 func (tv TypeAndValue) IsType() bool {
405 return tv.mode == typexpr
406 }
407 408 // IsBuiltin reports whether the corresponding expression denotes
409 // a (possibly parenthesized) built-in function.
410 func (tv TypeAndValue) IsBuiltin() bool {
411 return tv.mode == builtin
412 }
413 414 // IsValue reports whether the corresponding expression is a value.
415 // Builtins are not considered values. Constant values have a non-
416 // nil Value.
417 func (tv TypeAndValue) IsValue() bool {
418 switch tv.mode {
419 case constant_, variable, mapindex, value, commaok, commaerr:
420 return true
421 }
422 return false
423 }
424 425 // IsNil reports whether the corresponding expression denotes the
426 // predeclared value nil.
427 func (tv TypeAndValue) IsNil() bool {
428 return tv.mode == value && tv.Type == Typ[UntypedNil]
429 }
430 431 // Addressable reports whether the corresponding expression
432 // is addressable (https://golang.org/ref/spec#Address_operators).
433 func (tv TypeAndValue) Addressable() bool {
434 return tv.mode == variable
435 }
436 437 // Assignable reports whether the corresponding expression
438 // is assignable to (provided a value of the right type).
439 func (tv TypeAndValue) Assignable() bool {
440 return tv.mode == variable || tv.mode == mapindex
441 }
442 443 // HasOk reports whether the corresponding expression may be
444 // used on the rhs of a comma-ok assignment.
445 func (tv TypeAndValue) HasOk() bool {
446 return tv.mode == commaok || tv.mode == mapindex
447 }
448 449 // Instance reports the type arguments and instantiated type for type and
450 // function instantiations. For type instantiations, [Type] will be of dynamic
451 // type *[Named]. For function instantiations, [Type] will be of dynamic type
452 // *Signature.
453 type Instance struct {
454 TypeArgs *TypeList
455 Type Type
456 }
457 458 // An Initializer describes a package-level variable, or a list of variables in case
459 // of a multi-valued initialization expression, and the corresponding initialization
460 // expression.
461 type Initializer struct {
462 Lhs []*Var // var Lhs = Rhs
463 Rhs ast.Expr
464 }
465 466 func (init *Initializer) String() string {
467 var buf bytes.Buffer
468 for i, lhs := range init.Lhs {
469 if i > 0 {
470 buf.WriteString(", ")
471 }
472 buf.WriteString(lhs.Name())
473 }
474 buf.WriteString(" = ")
475 WriteExpr(&buf, init.Rhs)
476 return buf.String()
477 }
478 479 // Check type-checks a package and returns the resulting package object and
480 // the first error if any. Additionally, if info != nil, Check populates each
481 // of the non-nil maps in the [Info] struct.
482 //
483 // The package is marked as complete if no errors occurred, otherwise it is
484 // incomplete. See [Config.Error] for controlling behavior in the presence of
485 // errors.
486 //
487 // The package is specified by a list of *ast.Files and corresponding
488 // file set, and the package path the package is identified with.
489 // The clean path must not be empty or dot (".").
490 func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, info *Info) (*Package, error) {
491 pkg := NewPackage(path, "")
492 return pkg, NewChecker(conf, fset, pkg, info).Files(files)
493 }
494