Golang Var.Pos方法代码示例

func getDeclareStructOrInterface(prog *loader.Program, v *types.Var) string {
	// From x/tools/refactor/rename/check.go(checkStructField)#L288
	// 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.
	_, path, _ := prog.PathEnclosingInterval(v.Pos(), v.Pos())
	// path matches this pattern:
	// [Ident SelectorExpr? StarExpr? Field FieldList StructType ParenExpr* ... File]

	// Ascend to FieldList.
	var i int
	for {
		if _, ok := path[i].(*ast.FieldList); ok {
			break
		}
		i++
	}
	i++
	_ = path[i].(*ast.StructType)
	i++
	for {
		if _, ok := path[i].(*ast.ParenExpr); !ok {
			break
		}
		i++
	}
	if spec, ok := path[i].(*ast.TypeSpec); ok {
		return spec.Name.String()
	}
	return ""
}

// 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.)
//
// If the identifier is a field selector and its base expression is
// non-addressable, then VarValue returns the value of that field.
// For example:
//    func f() struct {x int}
//    f().x  // VarValue(x) returns a *Field instruction of type int
//
// All other identifiers denote addressable locations (variables).
// For them, VarValue may return either the variable's address or its
// value, even when the expression is evaluated only for its value; the
// situation is reported by isAddr, the second component of the result.
//
// If !isAddr, the returned value is the one associated with the
// specific identifier.  For example,
//       var x int    // VarValue(x) returns Const 0 here
//       x = 1        // VarValue(x) returns Const 1 here
//
// It is not specified whether the value or the address is returned in
// any particular case, as it may depend upon optimizations performed
// during SSA code generation, such as registerization, constant
// folding, avoidance of materialization of subexpressions, etc.
//
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 *Unexporter) checkStructField(objsToUpdate map[types.Object]string, from *types.Var, to string) {
	// 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 matches this pattern:
	// [Ident SelectorExpr? StarExpr? Field FieldList StructType ParenExpr* ... File]

	// Ascend to FieldList.
	var i int
	for {
		if _, ok := path[i].(*ast.FieldList); ok {
			break
		}
		i++
	}
	i++
	tStruct := path[i].(*ast.StructType)
	i++
	// Ascend past parens (unlikely).
	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, to)
		if len(indices) == 1 {
			r.warn(from,
				r.errorf(from.Pos(), "renaming this field %q to %q",
					from.Name(), 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[tStruct].Type.Underlying().(*types.Struct)
		for i := 0; i < t.NumFields(); i++ {
			if prev := t.Field(i); prev.Name() == to {
				r.warn(from,
					r.errorf(from.Pos(), "renaming this field %q to %q",
						from.Name(), 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(objsToUpdate, named.Obj(), to)
		} else if named, ok := deref(from.Type()).(*types.Named); ok {
			r.check(objsToUpdate, named.Obj(), to)
		}
	}

	// Check integrity of existing (field and method) selections.
	r.checkSelections(objsToUpdate, from, to)
}