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 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 path. 61 // The semantics is like for ImporterFrom.ImportFrom except that 62 // dir and mode are ignored (since they are not present). 63 Import(path string) (*Package, error) 64 } 65 66 // ImportMode is reserved for future use. 67 type ImportMode int 68 69 // An ImporterFrom resolves import paths to packages; it 70 // supports vendoring per https://golang.org/s/go15vendor. 71 // Use go/importer to obtain an ImporterFrom implementation. 72 type ImporterFrom interface { 73 // Importer is present for backward-compatibility. Calling 74 // Import(path) is the same as calling ImportFrom(path, "", 0); 75 // i.e., locally vendored packages may not be found. 76 // The types package does not call Import if an ImporterFrom 77 // is present. 78 Importer 79 80 // ImportFrom returns the imported package for the given import 81 // path when imported by a package file located in dir. 82 // If the import failed, besides returning an error, ImportFrom 83 // is encouraged to cache and return a package anyway, if one 84 // was created. This will reduce package inconsistencies and 85 // follow-on type checker errors due to the missing package. 86 // The mode value must be 0; it is reserved for future use. 87 // Two calls to ImportFrom with the same path and dir must 88 // return the same package. 89 ImportFrom(path, dir string, mode ImportMode) (*Package, error) 90 } 91 92 // A Config specifies the configuration for type checking. 93 // The zero value for Config is a ready-to-use default configuration. 94 type Config struct { 95 // If IgnoreFuncBodies is set, function bodies are not 96 // type-checked. 97 IgnoreFuncBodies bool 98 99 // If FakeImportC is set, `import "C"` (for packages requiring Cgo) 100 // declares an empty "C" package and errors are omitted for qualified 101 // identifiers referring to package C (which won't find an object). 102 // This feature is intended for the standard library cmd/api tool. 103 // 104 // Caution: Effects may be unpredictable due to follow-on errors. 105 // Do not use casually! 106 FakeImportC bool 107 108 // If Error != nil, it is called with each error found 109 // during type checking; err has dynamic type Error. 110 // Secondary errors (for instance, to enumerate all types 111 // involved in an invalid recursive type declaration) have 112 // error strings that start with a '\t' character. 113 // If Error == nil, type-checking stops with the first 114 // error found. 115 Error func(err error) 116 117 // An importer is used to import packages referred to from 118 // import declarations. 119 // If the installed importer implements ImporterFrom, the type 120 // checker calls ImportFrom instead of Import. 121 // The type checker reports an error if an importer is needed 122 // but none was installed. 123 Importer Importer 124 125 // If Sizes != nil, it provides the sizing functions for package unsafe. 126 // Otherwise SizesFor("gc", "amd64") is used instead. 127 Sizes Sizes 128 129 // If DisableUnusedImportCheck is set, packages are not checked 130 // for unused imports. 131 DisableUnusedImportCheck bool 132 } 133 134 // Info holds result type information for a type-checked package. 135 // Only the information for which a map is provided is collected. 136 // If the package has type errors, the collected information may 137 // be incomplete. 138 type Info struct { 139 // Types maps expressions to their types, and for constant 140 // expressions, also their values. Invalid expressions are 141 // omitted. 142 // 143 // For (possibly parenthesized) identifiers denoting built-in 144 // functions, the recorded signatures are call-site specific: 145 // if the call result is not a constant, the recorded type is 146 // an argument-specific signature. Otherwise, the recorded type 147 // is invalid. 148 // 149 // The Types map does not record the type of every identifier, 150 // only those that appear where an arbitrary expression is 151 // permitted. For instance, the identifier f in a selector 152 // expression x.f is found only in the Selections map, the 153 // identifier z in a variable declaration 'var z int' is found 154 // only in the Defs map, and identifiers denoting packages in 155 // qualified identifiers are collected in the Uses map. 156 Types map[ast.Expr]TypeAndValue 157 158 // Defs maps identifiers to the objects they define (including 159 // package names, dots "." of dot-imports, and blank "_" identifiers). 160 // For identifiers that do not denote objects (e.g., the package name 161 // in package clauses, or symbolic variables t in t := x.(type) of 162 // type switch headers), the corresponding objects are nil. 163 // 164 // For an embedded field, Defs returns the field *Var it defines. 165 // 166 // Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos() 167 Defs map[*ast.Ident]Object 168 169 // Uses maps identifiers to the objects they denote. 170 // 171 // For an embedded field, Uses returns the *TypeName it denotes. 172 // 173 // Invariant: Uses[id].Pos() != id.Pos() 174 Uses map[*ast.Ident]Object 175 176 // Implicits maps nodes to their implicitly declared objects, if any. 177 // The following node and object types may appear: 178 // 179 // node declared object 180 // 181 // *ast.ImportSpec *PkgName for imports without renames 182 // *ast.CaseClause type-specific *Var for each type switch case clause (incl. default) 183 // *ast.Field anonymous parameter *Var (incl. unnamed results) 184 // 185 Implicits map[ast.Node]Object 186 187 // Selections maps selector expressions (excluding qualified identifiers) 188 // to their corresponding selections. 189 Selections map[*ast.SelectorExpr]*Selection 190 191 // Scopes maps ast.Nodes to the scopes they define. Package scopes are not 192 // associated with a specific node but with all files belonging to a package. 193 // Thus, the package scope can be found in the type-checked Package object. 194 // Scopes nest, with the Universe scope being the outermost scope, enclosing 195 // the package scope, which contains (one or more) files scopes, which enclose 196 // function scopes which in turn enclose statement and function literal scopes. 197 // Note that even though package-level functions are declared in the package 198 // scope, the function scopes are embedded in the file scope of the file 199 // containing the function declaration. 200 // 201 // The following node types may appear in Scopes: 202 // 203 // *ast.File 204 // *ast.FuncType 205 // *ast.BlockStmt 206 // *ast.IfStmt 207 // *ast.SwitchStmt 208 // *ast.TypeSwitchStmt 209 // *ast.CaseClause 210 // *ast.CommClause 211 // *ast.ForStmt 212 // *ast.RangeStmt 213 // 214 Scopes map[ast.Node]*Scope 215 216 // InitOrder is the list of package-level initializers in the order in which 217 // they must be executed. Initializers referring to variables related by an 218 // initialization dependency appear in topological order, the others appear 219 // in source order. Variables without an initialization expression do not 220 // appear in this list. 221 InitOrder []*Initializer 222 } 223 224 // TypeOf returns the type of expression e, or nil if not found. 225 // Precondition: the Types, Uses and Defs maps are populated. 226 // 227 func (info *Info) TypeOf(e ast.Expr) Type { 228 if t, ok := info.Types[e]; ok { 229 return t.Type 230 } 231 if id, _ := e.(*ast.Ident); id != nil { 232 if obj := info.ObjectOf(id); obj != nil { 233 return obj.Type() 234 } 235 } 236 return nil 237 } 238 239 // ObjectOf returns the object denoted by the specified id, 240 // or nil if not found. 241 // 242 // If id is an embedded struct field, ObjectOf returns the field (*Var) 243 // it defines, not the type (*TypeName) it uses. 244 // 245 // Precondition: the Uses and Defs maps are populated. 246 // 247 func (info *Info) ObjectOf(id *ast.Ident) Object { 248 if obj := info.Defs[id]; obj != nil { 249 return obj 250 } 251 return info.Uses[id] 252 } 253 254 // TypeAndValue reports the type and value (for constants) 255 // of the corresponding expression. 256 type TypeAndValue struct { 257 mode operandMode 258 Type Type 259 Value constant.Value 260 } 261 262 // TODO(gri) Consider eliminating the IsVoid predicate. Instead, report 263 // "void" values as regular values but with the empty tuple type. 264 265 // IsVoid reports whether the corresponding expression 266 // is a function call without results. 267 func (tv TypeAndValue) IsVoid() bool { 268 return tv.mode == novalue 269 } 270 271 // IsType reports whether the corresponding expression specifies a type. 272 func (tv TypeAndValue) IsType() bool { 273 return tv.mode == typexpr 274 } 275 276 // IsBuiltin reports whether the corresponding expression denotes 277 // a (possibly parenthesized) built-in function. 278 func (tv TypeAndValue) IsBuiltin() bool { 279 return tv.mode == builtin 280 } 281 282 // IsValue reports whether the corresponding expression is a value. 283 // Builtins are not considered values. Constant values have a non- 284 // nil Value. 285 func (tv TypeAndValue) IsValue() bool { 286 switch tv.mode { 287 case constant_, variable, mapindex, value, commaok: 288 return true 289 } 290 return false 291 } 292 293 // IsNil reports whether the corresponding expression denotes the 294 // predeclared value nil. 295 func (tv TypeAndValue) IsNil() bool { 296 return tv.mode == value && tv.Type == Typ[UntypedNil] 297 } 298 299 // Addressable reports whether the corresponding expression 300 // is addressable (https://golang.org/ref/spec#Address_operators). 301 func (tv TypeAndValue) Addressable() bool { 302 return tv.mode == variable 303 } 304 305 // Assignable reports whether the corresponding expression 306 // is assignable to (provided a value of the right type). 307 func (tv TypeAndValue) Assignable() bool { 308 return tv.mode == variable || tv.mode == mapindex 309 } 310 311 // HasOk reports whether the corresponding expression may be 312 // used on the rhs of a comma-ok assignment. 313 func (tv TypeAndValue) HasOk() bool { 314 return tv.mode == commaok || tv.mode == mapindex 315 } 316 317 // An Initializer describes a package-level variable, or a list of variables in case 318 // of a multi-valued initialization expression, and the corresponding initialization 319 // expression. 320 type Initializer struct { 321 Lhs []*Var // var Lhs = Rhs 322 Rhs ast.Expr 323 } 324 325 func (init *Initializer) String() string { 326 var buf bytes.Buffer 327 for i, lhs := range init.Lhs { 328 if i > 0 { 329 buf.WriteString(", ") 330 } 331 buf.WriteString(lhs.Name()) 332 } 333 buf.WriteString(" = ") 334 WriteExpr(&buf, init.Rhs) 335 return buf.String() 336 } 337 338 // Check type-checks a package and returns the resulting package object and 339 // the first error if any. Additionally, if info != nil, Check populates each 340 // of the non-nil maps in the Info struct. 341 // 342 // The package is marked as complete if no errors occurred, otherwise it is 343 // incomplete. See Config.Error for controlling behavior in the presence of 344 // errors. 345 // 346 // The package is specified by a list of *ast.Files and corresponding 347 // file set, and the package path the package is identified with. 348 // The clean path must not be empty or dot ("."). 349 func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, info *Info) (*Package, error) { 350 pkg := NewPackage(path, "") 351 return pkg, NewChecker(conf, fset, pkg, info).Files(files) 352 } 353 354 // AssertableTo reports whether a value of type V can be asserted to have type T. 355 func AssertableTo(V *Interface, T Type) bool { 356 m, _ := (*Checker)(nil).assertableTo(V, T) 357 return m == nil 358 } 359 360 // AssignableTo reports whether a value of type V is assignable to a variable of type T. 361 func AssignableTo(V, T Type) bool { 362 x := operand{mode: value, typ: V} 363 return x.assignableTo(nil, T, nil) // check not needed for non-constant x 364 } 365 366 // ConvertibleTo reports whether a value of type V is convertible to a value of type T. 367 func ConvertibleTo(V, T Type) bool { 368 x := operand{mode: value, typ: V} 369 return x.convertibleTo(nil, T) // check not needed for non-constant x 370 } 371 372 // Implements reports whether type V implements interface T. 373 func Implements(V Type, T *Interface) bool { 374 f, _ := MissingMethod(V, T, true) 375 return f == nil 376 } 377