// 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 "go/types" import ( "bytes" "fmt" "go/ast" "go/constant" "go/token" ) // 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" } // 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 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, or an error if the package couldn't be imported. // Two calls to Import with the same path return the same // package. 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 the package in srcDir, or an error // if the package couldn't be imported. The mode value must // be 0; it is reserved for future use. // Two calls to ImportFrom with the same path and srcDir return // the same package. ImportFrom(path, srcDir 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 { // 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-up errors. // Do not use casually! FakeImportC 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 &StdSizes{WordSize: 8, MaxAlign: 8} is used instead. Sizes Sizes // If DisableUnusedImportCheck is set, packages are not checked // for unused imports. DisableUnusedImportCheck bool } // 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 // 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 anonymous 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 anonymous 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 dot-imports and imports without renames // *ast.CaseClause type-specific *Var for each type switch case clause (incl. default) // *ast.Field anonymous parameter *Var // 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 following node types may appear in Scopes: // // *ast.File // *ast.FuncType // *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 } // 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 anonymous struct field, ObjectOf returns the field (*Var) // it uses, not the type (*TypeName) it defines. // // 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] } // TypeAndValue reports the type and value (for constants) // of the corresponding expression. type TypeAndValue struct { mode operandMode Type Type Value constant.Value } // TODO(gri) Consider eliminating the IsVoid predicate. Instead, report // "void" values as regular values but with the empty tuple type. // 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: 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 lhs of a comma-ok assignment. func (tv TypeAndValue) HasOk() bool { return tv.mode == commaok || tv.mode == mapindex } // 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) } // AssertableTo reports whether a value of type V can be asserted to have type T. func AssertableTo(V *Interface, T Type) bool { m, _ := assertableTo(V, T) return m == nil } // AssignableTo reports whether a value of type V is assignable to a variable of type T. func AssignableTo(V, T Type) bool { x := operand{mode: value, typ: V} return x.assignableTo(nil, T, nil) // config not needed for non-constant x } // ConvertibleTo reports whether a value of type V is convertible to a value of type T. func ConvertibleTo(V, T Type) bool { x := operand{mode: value, typ: V} return x.convertibleTo(nil, T) // config not needed for non-constant x } // Implements reports whether type V implements interface T. func Implements(V Type, T *Interface) bool { f, _ := MissingMethod(V, T, true) return f == nil }