// VarValue returns the SSA Value that corresponds to a specific
// identifier denoting the source-level named variable obj.
//
// VarValue returns nil if a local variable was not found, perhaps
// because its package was not built, the debug information was not
// requested during SSA construction, or the value was optimized away.
//
// ref is the path to an ast.Ident (e.g. from PathEnclosingInterval),
// and that ident must resolve to obj.
//
// pkg is the package enclosing the reference. (A reference to a var
// may result in code, so we need to know where to find that code.)
//
// The Value of a defining (as opposed to referring) identifier is the
// value assigned to it in its definition.
//
// In many cases where the identifier appears in an lvalue context,
// the resulting Value is the var's address, not its value.
// For example, x in all these examples:
// x.y = 0
// x[0] = 0
// _ = x[:]
// x = X{}
// _ = &x
// x.method() (iff method is on &x)
// and all package-level vars. (This situation can be detected by
// comparing the types of the Var and Value.)
//
func (prog *Program) VarValue(obj *types.Var, pkg *Package, ref []ast.Node) Value {
id := ref[0].(*ast.Ident)
// Package-level variable?
if v := prog.packageLevelValue(obj); v != nil {
return v.(*Global)
}
// Must be a function-local variable.
// (e.g. local, parameter, or field selection e.f)
fn := EnclosingFunction(pkg, ref)
if fn == nil {
return nil // e.g. SSA not built
}
// Defining ident of a parameter?
if id.Pos() == obj.Pos() {
for _, param := range fn.Params {
if param.Object() == obj {
return param
}
}
}
// Other ident?
for _, b := range fn.Blocks {
for _, instr := range b.Instrs {
if ref, ok := instr.(*DebugRef); ok {
if ref.Pos() == id.Pos() {
return ref.X
}
}
}
}
return nil // e.g. debug info not requested, or var optimized away
}
// VarValue returns the SSA Value that corresponds to a specific
// identifier denoting the source-level named variable obj.
//
// VarValue returns nil if a local variable was not found, perhaps
// because its package was not built, the debug information was not
// requested during SSA construction, or the value was optimized away.
//
// ref is the path to an ast.Ident (e.g. from PathEnclosingInterval),
// and that ident must resolve to obj.
//
// pkg is the package enclosing the reference. (A reference to a var
// always occurs within a function, so we need to know where to find it.)
//
// The Value of a defining (as opposed to referring) identifier is the
// value assigned to it in its definition. Similarly, the Value of an
// identifier that is the LHS of an assignment is the value assigned
// to it in that statement. In all these examples, VarValue(x) returns
// the value of x and isAddr==false.
//
// var x X
// var x = X{}
// x := X{}
// x = X{}
//
// When an identifier appears in an lvalue context other than as the
// LHS of an assignment, the resulting Value is the var's address, not
// its value. This situation is reported by isAddr, the second
// component of the result. In these examples, VarValue(x) returns
// the address of x and isAddr==true.
//
// x.y = 0
// x[0] = 0
// _ = x[:] (where x is an array)
// _ = &x
// x.method() (iff method is on &x)
//
func (prog *Program) VarValue(obj *types.Var, pkg *Package, ref []ast.Node) (value Value, isAddr bool) {
// All references to a var are local to some function, possibly init.
fn := EnclosingFunction(pkg, ref)
if fn == nil {
return // e.g. def of struct field; SSA not built?
}
id := ref[0].(*ast.Ident)
// Defining ident of a parameter?
if id.Pos() == obj.Pos() {
for _, param := range fn.Params {
if param.Object() == obj {
return param, false
}
}
}
// Other ident?
for _, b := range fn.Blocks {
for _, instr := range b.Instrs {
if dr, ok := instr.(*DebugRef); ok {
if dr.Pos() == id.Pos() {
return dr.X, dr.IsAddr
}
}
}
}
// Defining ident of package-level var?
if v := prog.packageLevelValue(obj); v != nil {
return v.(*Global), true
}
return // e.g. debug info not requested, or var optimized away
}
// checkStructField checks that the field renaming will not cause
// conflicts at its declaration, or ambiguity or changes to any selection.
func (r *renamer) checkStructField(from *types.Var) {
// Check that the struct declaration is free of field conflicts,
// and field/method conflicts.
// go/types offers no easy way to get from a field (or interface
// method) to its declaring struct (or interface), so we must
// ascend the AST.
info, path, _ := r.iprog.PathEnclosingInterval(from.Pos(), from.Pos())
// path is [Ident Field FieldList StructType ... File]. Can't fail.
// Ascend past parens (unlikely).
i := 4
for {
_, ok := path[i].(*ast.ParenExpr)
if !ok {
break
}
i++
}
if spec, ok := path[i].(*ast.TypeSpec); ok {
// This struct is also a named type.
// We must check for direct (non-promoted) field/field
// and method/field conflicts.
named := info.Defs[spec.Name].Type()
prev, indices, _ := types.LookupFieldOrMethod(named, true, info.Pkg, r.to)
if len(indices) == 1 {
r.errorf(from.Pos(), "renaming this field %q to %q",
from.Name(), r.to)
r.errorf(prev.Pos(), "\twould conflict with this %s",
objectKind(prev))
return // skip checkSelections to avoid redundant errors
}
} else {
// This struct is not a named type.
// We need only check for direct (non-promoted) field/field conflicts.
T := info.Types[path[3].(*ast.StructType)].Type.Underlying().(*types.Struct)
for i := 0; i < T.NumFields(); i++ {
if prev := T.Field(i); prev.Name() == r.to {
r.errorf(from.Pos(), "renaming this field %q to %q",
from.Name(), r.to)
r.errorf(prev.Pos(), "\twould conflict with this field")
return // skip checkSelections to avoid redundant errors
}
}
}
// Renaming an anonymous field requires renaming the type too. e.g.
// print(s.T) // if we rename T to U,
// type T int // this and
// var s struct {T} // this must change too.
if from.Anonymous() {
if named, ok := from.Type().(*types.Named); ok {
r.check(named.Obj())
} else if named, ok := deref(from.Type()).(*types.Named); ok {
r.check(named.Obj())
}
}
// Check integrity of existing (field and method) selections.
r.checkSelections(from)
}