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 to the 14 // language object (Object) it denotes. 15 // Use Info.{Defs,Uses,Implicits} for the results of name resolution. 16 // 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. 20 // 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. 24 // 25 // For a tutorial, see https://golang.org/s/types-tutorial. 26 // 27 package types // import "go/types" 28 29 import ( 30 "bytes" 31 "fmt" 32 "go/ast" 33 "go/constant" 34 "go/token" 35 ) 36 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. 41 type Error struct { 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" 46 } 47 48 // Error returns an error string formatted as follows: 49 // filename:line:column: message 50 func (err Error) Error() string { 51 return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg) 52 } 53 54 // An Importer resolves import paths to Packages. 55 // 56 // CAUTION: This interface does not support the import of locally 57 // vendored packages. See https://golang.org/s/go15vendor. 58 // If possible, external implementations should implement ImporterFrom. 59 type Importer interface { 60 // Import returns the imported package for the given import 61 // path, or an error if the package couldn't be imported. 62 // Two calls to Import with the same path return the same 63 // package. 64 Import(path string) (*Package, error) 65 } 66 67 // ImportMode is reserved for future use. 68 type ImportMode int 69 70 // An ImporterFrom resolves import paths to packages; it 71 // supports vendoring per https://golang.org/s/go15vendor. 72 // Use go/importer to obtain an ImporterFrom implementation. 73 type ImporterFrom interface { 74 // Importer is present for backward-compatibility. Calling 75 // Import(path) is the same as calling ImportFrom(path, "", 0); 76 // i.e., locally vendored packages may not be found. 77 // The types package does not call Import if an ImporterFrom 78 // is present. 79 Importer 80 81 // ImportFrom returns the imported package for the given import 82 // path when imported by the package in srcDir, or an error 83 // if the package couldn't be imported. The mode value must 84 // be 0; it is reserved for future use. 85 // Two calls to ImportFrom with the same path and srcDir return 86 // the same package. 87 ImportFrom(path, srcDir string, mode ImportMode) (*Package, error) 88 } 89 90 // A Config specifies the configuration for type checking. 91 // The zero value for Config is a ready-to-use default configuration. 92 type Config struct { 93 // If IgnoreFuncBodies is set, function bodies are not 94 // type-checked. 95 IgnoreFuncBodies bool 96 97 // If FakeImportC is set, `import "C"` (for packages requiring Cgo) 98 // declares an empty "C" package and errors are omitted for qualified 99 // identifiers referring to package C (which won't find an object). 100 // This feature is intended for the standard library cmd/api tool. 101 // 102 // Caution: Effects may be unpredictable due to follow-up errors. 103 // Do not use casually! 104 FakeImportC bool 105 106 // If Error != nil, it is called with each error found 107 // during type checking; err has dynamic type Error. 108 // Secondary errors (for instance, to enumerate all types 109 // involved in an invalid recursive type declaration) have 110 // error strings that start with a '\t' character. 111 // If Error == nil, type-checking stops with the first 112 // error found. 113 Error func(err error) 114 115 // An importer is used to import packages referred to from 116 // import declarations. 117 // If the installed importer implements ImporterFrom, the type 118 // checker calls ImportFrom instead of Import. 119 // The type checker reports an error if an importer is needed 120 // but none was installed. 121 Importer Importer 122 123 // If Sizes != nil, it provides the sizing functions for package unsafe. 124 // Otherwise &StdSizes{WordSize: 8, MaxAlign: 8} is used instead. 125 Sizes Sizes 126 127 // If DisableUnusedImportCheck is set, packages are not checked 128 // for unused imports. 129 DisableUnusedImportCheck bool 130 } 131 132 // Info holds result type information for a type-checked package. 133 // Only the information for which a map is provided is collected. 134 // If the package has type errors, the collected information may 135 // be incomplete. 136 type Info struct { 137 // Types maps expressions to their types, and for constant 138 // expressions, also their values. Invalid expressions are 139 // omitted. 140 // 141 // For (possibly parenthesized) identifiers denoting built-in 142 // functions, the recorded signatures are call-site specific: 143 // if the call result is not a constant, the recorded type is 144 // an argument-specific signature. Otherwise, the recorded type 145 // is invalid. 146 // 147 // The Types map does not record the type of every identifier, 148 // only those that appear where an arbitrary expression is 149 // permitted. For instance, the identifier f in a selector 150 // expression x.f is found only in the Selections map, the 151 // identifier z in a variable declaration 'var z int' is found 152 // only in the Defs map, and identifiers denoting packages in 153 // qualified identifiers are collected in the Uses map. 154 Types map[ast.Expr]TypeAndValue 155 156 // Defs maps identifiers to the objects they define (including 157 // package names, dots "." of dot-imports, and blank "_" identifiers). 158 // For identifiers that do not denote objects (e.g., the package name 159 // in package clauses, or symbolic variables t in t := x.(type) of 160 // type switch headers), the corresponding objects are nil. 161 // 162 // For an anonymous field, Defs returns the field *Var it defines. 163 // 164 // Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos() 165 Defs map[*ast.Ident]Object 166 167 // Uses maps identifiers to the objects they denote. 168 // 169 // For an anonymous field, Uses returns the *TypeName it denotes. 170 // 171 // Invariant: Uses[id].Pos() != id.Pos() 172 Uses map[*ast.Ident]Object 173 174 // Implicits maps nodes to their implicitly declared objects, if any. 175 // The following node and object types may appear: 176 // 177 // node declared object 178 // 179 // *ast.ImportSpec *PkgName for dot-imports and imports without renames 180 // *ast.CaseClause type-specific *Var for each type switch case clause (incl. default) 181 // *ast.Field anonymous parameter *Var 182 // 183 Implicits map[ast.Node]Object 184 185 // Selections maps selector expressions (excluding qualified identifiers) 186 // to their corresponding selections. 187 Selections map[*ast.SelectorExpr]*Selection 188 189 // Scopes maps ast.Nodes to the scopes they define. Package scopes are not 190 // associated with a specific node but with all files belonging to a package. 191 // Thus, the package scope can be found in the type-checked Package object. 192 // Scopes nest, with the Universe scope being the outermost scope, enclosing 193 // the package scope, which contains (one or more) files scopes, which enclose 194 // function scopes which in turn enclose statement and function literal scopes. 195 // Note that even though package-level functions are declared in the package 196 // scope, the function scopes are embedded in the file scope of the file 197 // containing the function declaration. 198 // 199 // The following node types may appear in Scopes: 200 // 201 // *ast.File 202 // *ast.FuncType 203 // *ast.BlockStmt 204 // *ast.IfStmt 205 // *ast.SwitchStmt 206 // *ast.TypeSwitchStmt 207 // *ast.CaseClause 208 // *ast.CommClause 209 // *ast.ForStmt 210 // *ast.RangeStmt 211 // 212 Scopes map[ast.Node]*Scope 213 214 // InitOrder is the list of package-level initializers in the order in which 215 // they must be executed. Initializers referring to variables related by an 216 // initialization dependency appear in topological order, the others appear 217 // in source order. Variables without an initialization expression do not 218 // appear in this list. 219 InitOrder []*Initializer 220 } 221 222 // TypeOf returns the type of expression e, or nil if not found. 223 // Precondition: the Types, Uses and Defs maps are populated. 224 // 225 func (info *Info) TypeOf(e ast.Expr) Type { 226 if t, ok := info.Types[e]; ok { 227 return t.Type 228 } 229 if id, _ := e.(*ast.Ident); id != nil { 230 if obj := info.ObjectOf(id); obj != nil { 231 return obj.Type() 232 } 233 } 234 return nil 235 } 236 237 // ObjectOf returns the object denoted by the specified id, 238 // or nil if not found. 239 // 240 // If id is an anonymous struct field, ObjectOf returns the field (*Var) 241 // it uses, not the type (*TypeName) it defines. 242 // 243 // Precondition: the Uses and Defs maps are populated. 244 // 245 func (info *Info) ObjectOf(id *ast.Ident) Object { 246 if obj, _ := info.Defs[id]; obj != nil { 247 return obj 248 } 249 return info.Uses[id] 250 } 251 252 // TypeAndValue reports the type and value (for constants) 253 // of the corresponding expression. 254 type TypeAndValue struct { 255 mode operandMode 256 Type Type 257 Value constant.Value 258 } 259 260 // TODO(gri) Consider eliminating the IsVoid predicate. Instead, report 261 // "void" values as regular values but with the empty tuple type. 262 263 // IsVoid reports whether the corresponding expression 264 // is a function call without results. 265 func (tv TypeAndValue) IsVoid() bool { 266 return tv.mode == novalue 267 } 268 269 // IsType reports whether the corresponding expression specifies a type. 270 func (tv TypeAndValue) IsType() bool { 271 return tv.mode == typexpr 272 } 273 274 // IsBuiltin reports whether the corresponding expression denotes 275 // a (possibly parenthesized) built-in function. 276 func (tv TypeAndValue) IsBuiltin() bool { 277 return tv.mode == builtin 278 } 279 280 // IsValue reports whether the corresponding expression is a value. 281 // Builtins are not considered values. Constant values have a non- 282 // nil Value. 283 func (tv TypeAndValue) IsValue() bool { 284 switch tv.mode { 285 case constant_, variable, mapindex, value, commaok: 286 return true 287 } 288 return false 289 } 290 291 // IsNil reports whether the corresponding expression denotes the 292 // predeclared value nil. 293 func (tv TypeAndValue) IsNil() bool { 294 return tv.mode == value && tv.Type == Typ[UntypedNil] 295 } 296 297 // Addressable reports whether the corresponding expression 298 // is addressable (https://golang.org/ref/spec#Address_operators). 299 func (tv TypeAndValue) Addressable() bool { 300 return tv.mode == variable 301 } 302 303 // Assignable reports whether the corresponding expression 304 // is assignable to (provided a value of the right type). 305 func (tv TypeAndValue) Assignable() bool { 306 return tv.mode == variable || tv.mode == mapindex 307 } 308 309 // HasOk reports whether the corresponding expression may be 310 // used on the lhs of a comma-ok assignment. 311 func (tv TypeAndValue) HasOk() bool { 312 return tv.mode == commaok || tv.mode == mapindex 313 } 314 315 // An Initializer describes a package-level variable, or a list of variables in case 316 // of a multi-valued initialization expression, and the corresponding initialization 317 // expression. 318 type Initializer struct { 319 Lhs []*Var // var Lhs = Rhs 320 Rhs ast.Expr 321 } 322 323 func (init *Initializer) String() string { 324 var buf bytes.Buffer 325 for i, lhs := range init.Lhs { 326 if i > 0 { 327 buf.WriteString(", ") 328 } 329 buf.WriteString(lhs.Name()) 330 } 331 buf.WriteString(" = ") 332 WriteExpr(&buf, init.Rhs) 333 return buf.String() 334 } 335 336 // Check type-checks a package and returns the resulting package object and 337 // the first error if any. Additionally, if info != nil, Check populates each 338 // of the non-nil maps in the Info struct. 339 // 340 // The package is marked as complete if no errors occurred, otherwise it is 341 // incomplete. See Config.Error for controlling behavior in the presence of 342 // errors. 343 // 344 // The package is specified by a list of *ast.Files and corresponding 345 // file set, and the package path the package is identified with. 346 // The clean path must not be empty or dot ("."). 347 func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, info *Info) (*Package, error) { 348 pkg := NewPackage(path, "") 349 return pkg, NewChecker(conf, fset, pkg, info).Files(files) 350 } 351 352 // AssertableTo reports whether a value of type V can be asserted to have type T. 353 func AssertableTo(V *Interface, T Type) bool { 354 m, _ := assertableTo(V, T) 355 return m == nil 356 } 357 358 // AssignableTo reports whether a value of type V is assignable to a variable of type T. 359 func AssignableTo(V, T Type) bool { 360 x := operand{mode: value, typ: V} 361 return x.assignableTo(nil, T, nil) // config not needed for non-constant x 362 } 363 364 // ConvertibleTo reports whether a value of type V is convertible to a value of type T. 365 func ConvertibleTo(V, T Type) bool { 366 x := operand{mode: value, typ: V} 367 return x.convertibleTo(nil, T) // config not needed for non-constant x 368 } 369 370 // Implements reports whether type V implements interface T. 371 func Implements(V Type, T *Interface) bool { 372 f, _ := MissingMethod(V, T, true) 373 return f == nil 374 } 375