// describe describes the syntax node denoted by the query position,
// including:
// - its syntactic category
// - the location of the definition of its referent (for identifiers)
// - its type and method set (for an expression or type expression)
// - its points-to set (for a pointer-like expression)
// - its dynamic types (for an interface, reflect.Value, or
// reflect.Type expression) and their points-to sets.
//
// All printed sets are sorted to ensure determinism.
//
func describe(o *Oracle, qpos *QueryPos) (queryResult, error) {
if false { // debugging
o.fprintf(os.Stderr, qpos.path[0], "you selected: %s %s",
importer.NodeDescription(qpos.path[0]), pathToString2(qpos.path))
}
path, action := findInterestingNode(qpos.info, qpos.path)
switch action {
case actionExpr:
return describeValue(o, qpos, path)
case actionType:
return describeType(o, qpos, path)
case actionPackage:
return describePackage(o, qpos, path)
case actionStmt:
return describeStmt(o, qpos, path)
case actionUnknown:
return &describeUnknownResult{path[0]}, nil
default:
panic(action) // unreachable
}
}
// ParseQueryPos parses the source query position pos.
// If needExact, it must identify a single AST subtree.
//
func ParseQueryPos(imp *importer.Importer, pos string, needExact bool) (*QueryPos, error) {
start, end, err := parseQueryPos(imp.Fset, pos)
if err != nil {
return nil, err
}
info, path, exact := imp.PathEnclosingInterval(start, end)
if path == nil {
return nil, fmt.Errorf("no syntax here")
}
if needExact && !exact {
return nil, fmt.Errorf("ambiguous selection within %s", importer.NodeDescription(path[0]))
}
return &QueryPos{start, end, info, path}, nil
}
func describeStmt(o *Oracle, qpos *QueryPos, path []ast.Node) (*describeStmtResult, error) {
var description string
switch n := path[0].(type) {
case *ast.Ident:
if qpos.info.ObjectOf(n).Pos() == n.Pos() {
description = "labelled statement"
} else {
description = "reference to labelled statement"
}
default:
// Nothing much to say about statements.
description = importer.NodeDescription(n)
}
return &describeStmtResult{o.prog.Fset, path[0], description}, nil
}
func (r *describeValueResult) toSerial(res *serial.Result, fset *token.FileSet) {
var value, objpos, ptaerr string
if r.constVal != nil {
value = r.constVal.String()
}
if r.obj != nil {
objpos = fset.Position(r.obj.Pos()).String()
}
if r.ptaErr != nil {
ptaerr = r.ptaErr.Error()
}
var pts []*serial.DescribePointer
for _, ptr := range r.ptrs {
var namePos string
if nt, ok := deref(ptr.typ).(*types.Named); ok {
namePos = fset.Position(nt.Obj().Pos()).String()
}
var labels []serial.DescribePTALabel
for _, l := range ptr.labels {
labels = append(labels, serial.DescribePTALabel{
Pos: fset.Position(l.Pos()).String(),
Desc: l.String(),
})
}
pts = append(pts, &serial.DescribePointer{
Type: ptr.typ.String(),
NamePos: namePos,
Labels: labels,
})
}
res.Describe = &serial.Describe{
Desc: importer.NodeDescription(r.expr),
Pos: fset.Position(r.expr.Pos()).String(),
Detail: "value",
Value: &serial.DescribeValue{
Type: r.typ.String(),
Value: value,
ObjPos: objpos,
PTAErr: ptaerr,
PTS: pts,
},
}
}
func (r *describeUnknownResult) toSerial(res *serial.Result, fset *token.FileSet) {
res.Describe = &serial.Describe{
Desc: importer.NodeDescription(r.node),
Pos: fset.Position(r.node.Pos()).String(),
}
}
func (r *describeUnknownResult) display(printf printfFunc) {
// Nothing much to say about misc syntax.
printf(r.node, "%s", importer.NodeDescription(r.node))
}
func (r *describeValueResult) display(printf printfFunc) {
var prefix, suffix string
if r.constVal != nil {
suffix = fmt.Sprintf(" of constant value %s", r.constVal)
}
switch obj := r.obj.(type) {
case *types.Func:
if recv := obj.Type().(*types.Signature).Recv(); recv != nil {
if _, ok := recv.Type().Underlying().(*types.Interface); ok {
prefix = "interface method "
} else {
prefix = "method "
}
}
case *types.Var:
// TODO(adonovan): go/types should make it simple to
// ask: IsStructField(*Var)?
if false {
prefix = "struct field "
}
}
// Describe the expression.
if r.obj != nil {
if r.obj.Pos() == r.expr.Pos() {
// defining ident
printf(r.expr, "definition of %s%s%s", prefix, r.obj, suffix)
} else {
// referring ident
printf(r.expr, "reference to %s%s%s", prefix, r.obj, suffix)
if def := r.obj.Pos(); def != token.NoPos {
printf(def, "defined here")
}
}
} else {
desc := importer.NodeDescription(r.expr)
if suffix != "" {
// constant expression
printf(r.expr, "%s%s", desc, suffix)
} else {
// non-constant expression
printf(r.expr, "%s of type %s", desc, r.typ)
}
}
// pointer analysis could not be run
if r.ptaErr != nil {
printf(r.expr, "no points-to information: %s", r.ptaErr)
return
}
if r.ptrs == nil {
return // PTA was not invoked (not an error)
}
// Display the results of pointer analysis.
if pointer.CanHaveDynamicTypes(r.typ) {
// Show concrete types for interface, reflect.Type or
// reflect.Value expression.
if len(r.ptrs) > 0 {
printf(r.qpos, "this %s may contain these dynamic types:", r.typ)
for _, ptr := range r.ptrs {
var obj types.Object
if nt, ok := deref(ptr.typ).(*types.Named); ok {
obj = nt.Obj()
}
if len(ptr.labels) > 0 {
printf(obj, "\t%s, may point to:", ptr.typ)
printLabels(printf, ptr.labels, "\t\t")
} else {
printf(obj, "\t%s", ptr.typ)
}
}
} else {
printf(r.qpos, "this %s cannot contain any dynamic types.", r.typ)
}
} else {
// Show labels for other expressions.
if ptr := r.ptrs[0]; len(ptr.labels) > 0 {
printf(r.qpos, "value may point to these labels:")
printLabels(printf, ptr.labels, "\t")
} else {
printf(r.qpos, "value cannot point to anything.")
}
}
}