// distanceFrom returns the column difference between from and p.pos (the current
// estimated position) if both are on the same line; if they are on different lines
// (or unknown) the result is infinity.
func (p *printer) distanceFrom(from token.Pos) int {
if from.IsValid() && p.pos.IsValid() {
if f := p.posFor(from); f.Line == p.pos.Line {
return p.pos.Column - f.Column
}
}
return infinity
}
// LookupParent follows the parent chain of scopes starting with s until
// it finds a scope where Lookup(name) returns a non-nil object, and then
// returns that scope and object. If a valid position pos is provided,
// only objects that were declared at or before pos are considered.
// If no such scope and object exists, the result is (nil, nil).
//
// Note that obj.Parent() may be different from the returned scope if the
// object was inserted into the scope and already had a parent at that
// time (see Insert, below). This can only happen for dot-imported objects
// whose scope is the scope of the package that exported them.
func (s *Scope) LookupParent(name string, pos token.Pos) (*Scope, Object) {
for ; s != nil; s = s.parent {
if obj := s.elems[name]; obj != nil && (!pos.IsValid() || obj.scopePos() <= pos) {
return s, obj
}
}
return nil, nil
}
// Eval returns the type and, if constant, the value for the
// expression expr, evaluated at position pos of package pkg,
// which must have been derived from type-checking an AST with
// complete position information relative to the provided file
// set.
//
// If the expression contains function literals, their bodies
// are ignored (i.e., the bodies are not type-checked).
//
// If pkg == nil, the Universe scope is used and the provided
// position pos is ignored. If pkg != nil, and pos is invalid,
// the package scope is used. Otherwise, pos must belong to the
// package.
//
// An error is returned if pos is not within the package or
// if the node cannot be evaluated.
//
// Note: Eval should not be used instead of running Check to compute
// types and values, but in addition to Check. Eval will re-evaluate
// its argument each time, and it also does not know about the context
// in which an expression is used (e.g., an assignment). Thus, top-
// level untyped constants will return an untyped type rather then the
// respective context-specific type.
//
func Eval(fset *token.FileSet, pkg *Package, pos token.Pos, expr string) (tv TypeAndValue, err error) {
// determine scope
var scope *Scope
if pkg == nil {
scope = Universe
pos = token.NoPos
} else if !pos.IsValid() {
scope = pkg.scope
} else {
// The package scope extent (position information) may be
// incorrect (files spread accross a wide range of fset
// positions) - ignore it and just consider its children
// (file scopes).
for _, fscope := range pkg.scope.children {
if scope = fscope.Innermost(pos); scope != nil {
break
}
}
if scope == nil || debug {
s := scope
for s != nil && s != pkg.scope {
s = s.parent
}
// s == nil || s == pkg.scope
if s == nil {
return TypeAndValue{}, fmt.Errorf("no position %s found in package %s", fset.Position(pos), pkg.name)
}
}
}
// parse expressions
node, err := parser.ParseExprFrom(fset, "eval", expr, 0)
if err != nil {
return TypeAndValue{}, err
}
// initialize checker
check := NewChecker(nil, fset, pkg, nil)
check.scope = scope
check.pos = pos
defer check.handleBailout(&err)
// evaluate node
var x operand
check.rawExpr(&x, node, nil)
return TypeAndValue{x.mode, x.typ, x.val}, err
}
// argument checks passing of argument x to the i'th parameter of the given signature.
// If ellipsis is valid, the argument is followed by ... at that position in the call.
func (check *Checker) argument(sig *Signature, i int, x *operand, ellipsis token.Pos) {
n := sig.params.Len()
// determine parameter type
var typ Type
switch {
case i < n:
typ = sig.params.vars[i].typ
case sig.variadic:
typ = sig.params.vars[n-1].typ
if debug {
if _, ok := typ.(*Slice); !ok {
check.dump("%s: expected unnamed slice type, got %s", sig.params.vars[n-1].Pos(), typ)
}
}
default:
check.errorf(x.pos(), "too many arguments")
return
}
if ellipsis.IsValid() {
// argument is of the form x...
if i != n-1 {
check.errorf(ellipsis, "can only use ... with matching parameter")
return
}
switch t := x.typ.Underlying().(type) {
case *Slice:
// ok
case *Tuple:
check.errorf(ellipsis, "cannot use ... with %d-valued expression %s", t.Len(), x)
return
default:
check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
return
}
} else if sig.variadic && i >= n-1 {
// use the variadic parameter slice's element type
typ = typ.(*Slice).elem
}
if !check.assignment(x, typ) && x.mode != invalid {
check.errorf(x.pos(), "cannot pass argument %s to parameter of type %s", x, typ)
}
}
// If returnPos is valid, initVars is called to type-check the assignment of
// return expressions, and returnPos is the position of the return statement.
func (check *Checker) initVars(lhs []*Var, rhs []ast.Expr, returnPos token.Pos) {
l := len(lhs)
get, r, commaOk := unpack(func(x *operand, i int) { check.expr(x, rhs[i]) }, len(rhs), l == 2 && !returnPos.IsValid())
if get == nil || l != r {
// invalidate lhs and use rhs
for _, obj := range lhs {
if obj.typ == nil {
obj.typ = Typ[Invalid]
}
}
if get == nil {
return // error reported by unpack
}
check.useGetter(get, r)
if returnPos.IsValid() {
check.errorf(returnPos, "wrong number of return values (want %d, got %d)", l, r)
return
}
check.errorf(rhs[0].Pos(), "assignment count mismatch (%d vs %d)", l, r)
return
}
var x operand
if commaOk {
var a [2]Type
for i := range a {
get(&x, i)
a[i] = check.initVar(lhs[i], &x, returnPos.IsValid())
}
check.recordCommaOkTypes(rhs[0], a)
return
}
for i, lhs := range lhs {
get(&x, i)
check.initVar(lhs, &x, returnPos.IsValid())
}
}
// blockBranches processes a block's statement list and returns the set of outgoing forward jumps.
// all is the scope of all declared labels, parent the set of labels declared in the immediately
// enclosing block, and lstmt is the labeled statement this block is associated with (or nil).
func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *ast.LabeledStmt, list []ast.Stmt) []*ast.BranchStmt {
b := &block{parent: parent, lstmt: lstmt}
var (
varDeclPos token.Pos
fwdJumps, badJumps []*ast.BranchStmt
)
// All forward jumps jumping over a variable declaration are possibly
// invalid (they may still jump out of the block and be ok).
// recordVarDecl records them for the given position.
recordVarDecl := func(pos token.Pos) {
varDeclPos = pos
badJumps = append(badJumps[:0], fwdJumps...) // copy fwdJumps to badJumps
}
jumpsOverVarDecl := func(jmp *ast.BranchStmt) bool {
if varDeclPos.IsValid() {
for _, bad := range badJumps {
if jmp == bad {
return true
}
}
}
return false
}
blockBranches := func(lstmt *ast.LabeledStmt, list []ast.Stmt) {
// Unresolved forward jumps inside the nested block
// become forward jumps in the current block.
fwdJumps = append(fwdJumps, check.blockBranches(all, b, lstmt, list)...)
}
var stmtBranches func(ast.Stmt)
stmtBranches = func(s ast.Stmt) {
switch s := s.(type) {
case *ast.DeclStmt:
if d, _ := s.Decl.(*ast.GenDecl); d != nil && d.Tok == token.VAR {
recordVarDecl(d.Pos())
}
case *ast.LabeledStmt:
// declare non-blank label
if name := s.Label.Name; name != "_" {
lbl := NewLabel(s.Label.Pos(), check.pkg, name)
if alt := all.Insert(lbl); alt != nil {
check.softErrorf(lbl.pos, "label %s already declared", name)
check.reportAltDecl(alt)
// ok to continue
} else {
b.insert(s)
check.recordDef(s.Label, lbl)
}
// resolve matching forward jumps and remove them from fwdJumps
i := 0
for _, jmp := range fwdJumps {
if jmp.Label.Name == name {
// match
lbl.used = true
check.recordUse(jmp.Label, lbl)
if jumpsOverVarDecl(jmp) {
check.softErrorf(
jmp.Label.Pos(),
"goto %s jumps over variable declaration at line %d",
name,
check.fset.Position(varDeclPos).Line,
)
// ok to continue
}
} else {
// no match - record new forward jump
fwdJumps[i] = jmp
i++
}
}
fwdJumps = fwdJumps[:i]
lstmt = s
}
stmtBranches(s.Stmt)
case *ast.BranchStmt:
if s.Label == nil {
return // checked in 1st pass (check.stmt)
}
// determine and validate target
name := s.Label.Name
switch s.Tok {
case token.BREAK:
// spec: "If there is a label, it must be that of an enclosing
// "for", "switch", or "select" statement, and that is the one
// whose execution terminates."
valid := false
if t := b.enclosingTarget(name); t != nil {
switch t.Stmt.(type) {
case *ast.SwitchStmt, *ast.TypeSwitchStmt, *ast.SelectStmt, *ast.ForStmt, *ast.RangeStmt:
valid = true
}
}
if !valid {
check.errorf(s.Label.Pos(), "invalid break label %s", name)
return
}
case token.CONTINUE:
// spec: "If there is a label, it must be that of an enclosing
// "for" statement, and that is the one whose execution advances."
valid := false
if t := b.enclosingTarget(name); t != nil {
switch t.Stmt.(type) {
case *ast.ForStmt, *ast.RangeStmt:
valid = true
}
}
if !valid {
check.errorf(s.Label.Pos(), "invalid continue label %s", name)
return
}
case token.GOTO:
if b.gotoTarget(name) == nil {
// label may be declared later - add branch to forward jumps
fwdJumps = append(fwdJumps, s)
return
}
default:
check.invalidAST(s.Pos(), "branch statement: %s %s", s.Tok, name)
return
}
// record label use
obj := all.Lookup(name)
obj.(*Label).used = true
check.recordUse(s.Label, obj)
case *ast.AssignStmt:
if s.Tok == token.DEFINE {
recordVarDecl(s.Pos())
}
case *ast.BlockStmt:
blockBranches(lstmt, s.List)
case *ast.IfStmt:
stmtBranches(s.Body)
if s.Else != nil {
stmtBranches(s.Else)
}
case *ast.CaseClause:
blockBranches(nil, s.Body)
case *ast.SwitchStmt:
stmtBranches(s.Body)
case *ast.TypeSwitchStmt:
stmtBranches(s.Body)
case *ast.CommClause:
blockBranches(nil, s.Body)
case *ast.SelectStmt:
stmtBranches(s.Body)
case *ast.ForStmt:
stmtBranches(s.Body)
case *ast.RangeStmt:
stmtBranches(s.Body)
}
}
for _, s := range list {
stmtBranches(s)
}
return fwdJumps
}