go/types, types2: infer minimum default type for untyped arguments

[gostls13.git] / src / go / types / api.go

// 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 (
        "bytes"
        "fmt"
        "go/ast"
        "go/constant"
        "go/token"
        . "internal/types/errors"
)

// 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 (err Error) Error() string {
        return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg)
}

// An ArgumentError holds an error associated with an argument index.
type ArgumentError struct {
        Index int
        Err   error
}

func (e *ArgumentError) Error() string { return e.Err.Error() }
func (e *ArgumentError) Unwrap() error { return e.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 follow the format "go%d.%d" (e.g. "go1.12") or it must be
        // empty; an empty string disables Go language version checks.
        // If the format is invalid, invoking the type checker will cause a
        // panic.
        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 _InferMaxDefaultType is set, the minimum (smallest) default
        // type that fits all untyped constant arguments for the same type
        // parameter is selected in type inference. (go.dev/issue/58671)
        _InferMaxDefaultType bool
}

func srcimporter_setUsesCgo(conf *Config) {
        conf.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 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
}

// 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 embedded struct field, ObjectOf returns the field (*Var)
// it defines, not the type (*TypeName) it uses.
//
// 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
}

// 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, commaerr:
                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 rhs of a comma-ok assignment.
func (tv TypeAndValue) HasOk() bool {
        return tv.mode == commaok || tv.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 (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.
//
// The behavior of AssertableTo is unspecified in three cases:
//   - if T is Typ[Invalid]
//   - if V is a generalized interface; i.e., an interface that may only be used
//     as a type constraint in Go code
//   - if T is an uninstantiated generic type
func AssertableTo(V *Interface, T Type) bool {
        // Checker.newAssertableTo suppresses errors for invalid types, so we need special
        // handling here.
        if T.Underlying() == Typ[Invalid] {
                return false
        }
        return (*Checker)(nil).newAssertableTo(nopos, V, T, nil)
}

// AssignableTo reports whether a value of type V is assignable to a variable
// of type T.
//
// The behavior of AssignableTo is unspecified if V or T is Typ[Invalid] or an
// uninstantiated generic type.
func AssignableTo(V, T Type) bool {
        x := operand{mode: value, typ: V}
        ok, _ := x.assignableTo(nil, T, nil) // check not needed for non-constant x
        return ok
}

// ConvertibleTo reports whether a value of type V is convertible to a value of
// type T.
//
// The behavior of ConvertibleTo is unspecified if V or T is Typ[Invalid] or an
// uninstantiated generic type.
func ConvertibleTo(V, T Type) bool {
        x := operand{mode: value, typ: V}
        return x.convertibleTo(nil, T, nil) // check not needed for non-constant x
}

// Implements reports whether type V implements interface T.
//
// The behavior of Implements is unspecified if V is Typ[Invalid] or an uninstantiated
// generic type.
func Implements(V Type, T *Interface) bool {
        if T.Empty() {
                // All types (even Typ[Invalid]) implement the empty interface.
                return true
        }
        // Checker.implements suppresses errors for invalid types, so we need special
        // handling here.
        if V.Underlying() == Typ[Invalid] {
                return false
        }
        return (*Checker)(nil).implements(0, V, T, false, nil)
}

// Satisfies reports whether type V satisfies the constraint T.
//
// The behavior of Satisfies is unspecified if V is Typ[Invalid] or an uninstantiated
// generic type.
func Satisfies(V Type, T *Interface) bool {
        return (*Checker)(nil).implements(0, V, T, true, nil)
}

// Identical reports whether x and y are identical types.
// Receivers of Signature types are ignored.
func Identical(x, y Type) bool {
        var c comparer
        return c.identical(x, y, nil)
}

// IdenticalIgnoreTags reports whether x and y are identical types if tags are ignored.
// Receivers of Signature types are ignored.
func IdenticalIgnoreTags(x, y Type) bool {
        var c comparer
        c.ignoreTags = true
        return c.identical(x, y, nil)
}