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// Copyright 2014 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 eg
import (
"fmt"
"go/ast"
exact "go/constant"
"go/token"
"go/types"
"log"
"os"
"reflect"
"golang.org/x/tools/go/ast/astutil"
)
// matchExpr reports whether pattern x matches y.
//
// If tr.allowWildcards, Idents in x that refer to parameters are
// treated as wildcards, and match any y that is assignable to the
// parameter type; matchExpr records this correspondence in tr.env.
// Otherwise, matchExpr simply reports whether the two trees are
// equivalent.
//
// A wildcard appearing more than once in the pattern must
// consistently match the same tree.
//
func (tr *Transformer) matchExpr(x, y ast.Expr) bool {
if x == nil && y == nil {
return true
}
if x == nil || y == nil {
return false
}
x = unparen(x)
y = unparen(y)
// Is x a wildcard? (a reference to a 'before' parameter)
if xobj, ok := tr.wildcardObj(x); ok {
return tr.matchWildcard(xobj, y)
}
// Object identifiers (including pkg-qualified ones)
// are handled semantically, not syntactically.
xobj := isRef(x, tr.info)
yobj := isRef(y, tr.info)
if xobj != nil {
return xobj == yobj
}
if yobj != nil {
return false
}
// TODO(adonovan): audit: we cannot assume these ast.Exprs
// contain non-nil pointers. e.g. ImportSpec.Name may be a
// nil *ast.Ident.
if reflect.TypeOf(x) != reflect.TypeOf(y) {
return false
}
switch x := x.(type) {
case *ast.Ident:
log.Fatalf("unexpected Ident: %s", astString(tr.fset, x))
case *ast.BasicLit:
y := y.(*ast.BasicLit)
xval := exact.MakeFromLiteral(x.Value, x.Kind, 0)
yval := exact.MakeFromLiteral(y.Value, y.Kind, 0)
return exact.Compare(xval, token.EQL, yval)
case *ast.FuncLit:
// func literals (and thus statement syntax) never match.
return false
case *ast.CompositeLit:
y := y.(*ast.CompositeLit)
return (x.Type == nil) == (y.Type == nil) &&
(x.Type == nil || tr.matchType(x.Type, y.Type)) &&
tr.matchExprs(x.Elts, y.Elts)
case *ast.SelectorExpr:
y := y.(*ast.SelectorExpr)
return tr.matchSelectorExpr(x, y) &&
tr.info.Selections[x].Obj() == tr.info.Selections[y].Obj()
case *ast.IndexExpr:
y := y.(*ast.IndexExpr)
return tr.matchExpr(x.X, y.X) &&
tr.matchExpr(x.Index, y.Index)
case *ast.SliceExpr:
y := y.(*ast.SliceExpr)
return tr.matchExpr(x.X, y.X) &&
tr.matchExpr(x.Low, y.Low) &&
tr.matchExpr(x.High, y.High) &&
tr.matchExpr(x.Max, y.Max) &&
x.Slice3 == y.Slice3
case *ast.TypeAssertExpr:
y := y.(*ast.TypeAssertExpr)
return tr.matchExpr(x.X, y.X) &&
tr.matchType(x.Type, y.Type)
case *ast.CallExpr:
y := y.(*ast.CallExpr)
match := tr.matchExpr // function call
if tr.info.Types[x.Fun].IsType() {
match = tr.matchType // type conversion
}
return x.Ellipsis.IsValid() == y.Ellipsis.IsValid() &&
match(x.Fun, y.Fun) &&
tr.matchExprs(x.Args, y.Args)
case *ast.StarExpr:
y := y.(*ast.StarExpr)
return tr.matchExpr(x.X, y.X)
case *ast.UnaryExpr:
y := y.(*ast.UnaryExpr)
return x.Op == y.Op &&
tr.matchExpr(x.X, y.X)
case *ast.BinaryExpr:
y := y.(*ast.BinaryExpr)
return x.Op == y.Op &&
tr.matchExpr(x.X, y.X) &&
tr.matchExpr(x.Y, y.Y)
case *ast.KeyValueExpr:
y := y.(*ast.KeyValueExpr)
return tr.matchExpr(x.Key, y.Key) &&
tr.matchExpr(x.Value, y.Value)
}
panic(fmt.Sprintf("unhandled AST node type: %T", x))
}
func (tr *Transformer) matchExprs(xx, yy []ast.Expr) bool {
if len(xx) != len(yy) {
return false
}
for i := range xx {
if !tr.matchExpr(xx[i], yy[i]) {
return false
}
}
return true
}
// matchType reports whether the two type ASTs denote identical types.
func (tr *Transformer) matchType(x, y ast.Expr) bool {
tx := tr.info.Types[x].Type
ty := tr.info.Types[y].Type
return types.Identical(tx, ty)
}
func (tr *Transformer) wildcardObj(x ast.Expr) (*types.Var, bool) {
if x, ok := x.(*ast.Ident); ok && x != nil && tr.allowWildcards {
if xobj, ok := tr.info.Uses[x].(*types.Var); ok && tr.wildcards[xobj] {
return xobj, true
}
}
return nil, false
}
func (tr *Transformer) matchSelectorExpr(x, y *ast.SelectorExpr) bool {
if xobj, ok := tr.wildcardObj(x.X); ok {
field := x.Sel.Name
yt := tr.info.TypeOf(y.X)
o, _, _ := types.LookupFieldOrMethod(yt, true, tr.currentPkg, field)
if o != nil {
tr.env[xobj.Name()] = y.X // record binding
return true
}
}
return tr.matchExpr(x.X, y.X)
}
func (tr *Transformer) matchWildcard(xobj *types.Var, y ast.Expr) bool {
name := xobj.Name()
if tr.verbose {
fmt.Fprintf(os.Stderr, "%s: wildcard %s -> %s?: ",
tr.fset.Position(y.Pos()), name, astString(tr.fset, y))
}
// Check that y is assignable to the declared type of the param.
yt := tr.info.TypeOf(y)
if yt == nil {
// y has no type.
// Perhaps it is an *ast.Ellipsis in [...]T{}, or
// an *ast.KeyValueExpr in T{k: v}.
// Clearly these pseudo-expressions cannot match a
// wildcard, but it would nice if we had a way to ignore
// the difference between T{v} and T{k:v} for structs.
return false
}
if !types.AssignableTo(yt, xobj.Type()) {
if tr.verbose {
fmt.Fprintf(os.Stderr, "%s not assignable to %s\n", yt, xobj.Type())
}
return false
}
// A wildcard matches any expression.
// If it appears multiple times in the pattern, it must match
// the same expression each time.
if old, ok := tr.env[name]; ok {
// found existing binding
tr.allowWildcards = false
r := tr.matchExpr(old, y)
if tr.verbose {
fmt.Fprintf(os.Stderr, "%t secondary match, primary was %s\n",
r, astString(tr.fset, old))
}
tr.allowWildcards = true
return r
}
if tr.verbose {
fmt.Fprintf(os.Stderr, "primary match\n")
}
tr.env[name] = y // record binding
return true
}
// -- utilities --------------------------------------------------------
func unparen(e ast.Expr) ast.Expr { return astutil.Unparen(e) }
// isRef returns the object referred to by this (possibly qualified)
// identifier, or nil if the node is not a referring identifier.
func isRef(n ast.Node, info *types.Info) types.Object {
switch n := n.(type) {
case *ast.Ident:
return info.Uses[n]
case *ast.SelectorExpr:
if _, ok := info.Selections[n]; !ok {
// qualified ident
return info.Uses[n.Sel]
}
}
return nil
}