// 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 ( . ) // 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 ( Error) () string { return fmt.Sprintf("%s: %s", .Fset.Position(.Pos), .Msg) } // An ArgumentError holds an error associated with an argument index. type ArgumentError struct { Index int Err error } func ( *ArgumentError) () string { return .Err.Error() } func ( *ArgumentError) () error { return .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( *Config) { .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) () bool { return .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) ( ast.Expr) Type { if , := .Types[]; { return .Type } if , := .(*ast.Ident); != nil { if := .ObjectOf(); != nil { return .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) ( *ast.Ident) Object { if := .Defs[]; != nil { return } return .Uses[] } // 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) ( *ast.ImportSpec) *PkgName { var Object if .Name != nil { = .Defs[.Name] } else { = .Implicits[] } , := .(*PkgName) return } // 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 ( TypeAndValue) () bool { return .mode == novalue } // IsType reports whether the corresponding expression specifies a type. func ( TypeAndValue) () bool { return .mode == typexpr } // IsBuiltin reports whether the corresponding expression denotes // a (possibly parenthesized) built-in function. func ( TypeAndValue) () bool { return .mode == builtin } // IsValue reports whether the corresponding expression is a value. // Builtins are not considered values. Constant values have a non- // nil Value. func ( TypeAndValue) () bool { switch .mode { case constant_, variable, mapindex, value, commaok, commaerr: return true } return false } // IsNil reports whether the corresponding expression denotes the // predeclared value nil. func ( TypeAndValue) () bool { return .mode == value && .Type == Typ[UntypedNil] } // Addressable reports whether the corresponding expression // is addressable (https://golang.org/ref/spec#Address_operators). func ( TypeAndValue) () bool { return .mode == variable } // Assignable reports whether the corresponding expression // is assignable to (provided a value of the right type). func ( TypeAndValue) () bool { return .mode == variable || .mode == mapindex } // HasOk reports whether the corresponding expression may be // used on the rhs of a comma-ok assignment. func ( TypeAndValue) () bool { return .mode == commaok || .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 ( *Initializer) () string { var bytes.Buffer for , := range .Lhs { if > 0 { .WriteString(", ") } .WriteString(.Name()) } .WriteString(" = ") WriteExpr(&, .Rhs) return .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 ( *Config) ( string, *token.FileSet, []*ast.File, *Info) (*Package, error) { := NewPackage(, "") return , NewChecker(, , , ).Files() }