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// Copyright 2024 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 chautil provides helper functions related to
// class hierarchy analysis (CHA) for use in x/tools.
package chautil
import (
"go/types"
"golang.org/x/tools/go/ssa"
"golang.org/x/tools/go/types/typeutil"
)
// LazyCallees returns a function that maps a call site (in a function in fns)
// to its callees within fns. The set of callees is computed using the CHA algorithm,
// i.e., on the entire implements relation between interfaces and concrete types
// in fns. Please see golang.org/x/tools/go/callgraph/cha for more information.
//
// The resulting function is not concurrency safe.
func LazyCallees(fns map[*ssa.Function]bool) func(site ssa.CallInstruction) []*ssa.Function {
// funcsBySig contains all functions, keyed by signature. It is
// the effective set of address-taken functions used to resolve
// a dynamic call of a particular signature.
var funcsBySig typeutil.Map // value is []*ssa.Function
// methodsByID contains all methods, grouped by ID for efficient
// lookup.
//
// We must key by ID, not name, for correct resolution of interface
// calls to a type with two (unexported) methods spelled the same but
// from different packages. The fact that the concrete type implements
// the interface does not mean the call dispatches to both methods.
methodsByID := make(map[string][]*ssa.Function)
// An imethod represents an interface method I.m.
// (There's no go/types object for it;
// a *types.Func may be shared by many interfaces due to interface embedding.)
type imethod struct {
I *types.Interface
id string
}
// methodsMemo records, for every abstract method call I.m on
// interface type I, the set of concrete methods C.m of all
// types C that satisfy interface I.
//
// Abstract methods may be shared by several interfaces,
// hence we must pass I explicitly, not guess from m.
//
// methodsMemo is just a cache, so it needn't be a typeutil.Map.
methodsMemo := make(map[imethod][]*ssa.Function)
lookupMethods := func(I *types.Interface, m *types.Func) []*ssa.Function {
id := m.Id()
methods, ok := methodsMemo[imethod{I, id}]
if !ok {
for _, f := range methodsByID[id] {
C := f.Signature.Recv().Type() // named or *named
if types.Implements(C, I) {
methods = append(methods, f)
}
}
methodsMemo[imethod{I, id}] = methods
}
return methods
}
for f := range fns {
if f.Signature.Recv() == nil {
// Package initializers can never be address-taken.
if f.Name() == "init" && f.Synthetic == "package initializer" {
continue
}
funcs, _ := funcsBySig.At(f.Signature).([]*ssa.Function)
funcs = append(funcs, f)
funcsBySig.Set(f.Signature, funcs)
} else if obj := f.Object(); obj != nil {
id := obj.(*types.Func).Id()
methodsByID[id] = append(methodsByID[id], f)
}
}
return func(site ssa.CallInstruction) []*ssa.Function {
call := site.Common()
if call.IsInvoke() {
tiface := call.Value.Type().Underlying().(*types.Interface)
return lookupMethods(tiface, call.Method)
} else if g := call.StaticCallee(); g != nil {
return []*ssa.Function{g}
} else if _, ok := call.Value.(*ssa.Builtin); !ok {
fns, _ := funcsBySig.At(call.Signature()).([]*ssa.Function)
return fns
}
return nil
}
}
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