reflect: add support for DeepEqual

The implementation has been mostly copied from the Go reference
implementation with some small changes to fit TinyGo.

Source: https://github.com/golang/go/blob/77a11c05d6a6f766c75f804ea9b8796f9a9f85a3/src/reflect/deepequal.go

In addition, this commit also contains the following:

  - A set of tests copied from the Go reflect package.
  - An increased stack size for the riscv-qemu and hifive1-qemu targets
    (because they otherwise fail to run the tests). Because these
    targets are only used for testing, this seems fine to me.

src/reflect/deepequal.go

@@ -1,9 +1,196 @@
+// Copyright 2009 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.
+
+// Deep equality test via reflection
+
 package reflect
 
+import "unsafe"
+
+// During deepValueEqual, must keep track of checks that are
+// in progress. The comparison algorithm assumes that all
+// checks in progress are true when it reencounters them.
+// Visited comparisons are stored in a map indexed by visit.
+type visit struct {
+	a1  unsafe.Pointer
+	a2  unsafe.Pointer
+	typ rawType
+}
+
+// Tests for deep equality using reflected types. The map argument tracks
+// comparisons that have already been seen, which allows short circuiting on
+// recursive types.
+func deepValueEqual(v1, v2 Value, visited map[visit]struct{}) bool {
+	if !v1.IsValid() || !v2.IsValid() {
+		return v1.IsValid() == v2.IsValid()
+	}
+	if v1.typecode != v2.typecode {
+		return false
+	}
+
+	// We want to avoid putting more in the visited map than we need to.
+	// For any possible reference cycle that might be encountered,
+	// hard(v1, v2) needs to return true for at least one of the types in the cycle,
+	// and it's safe and valid to get Value's internal pointer.
+	hard := func(v1, v2 Value) bool {
+		switch v1.Kind() {
+		case Map, Slice, Ptr, Interface:
+			// Nil pointers cannot be cyclic. Avoid putting them in the visited map.
+			return !v1.IsNil() && !v2.IsNil()
+		}
+		return false
+	}
+
+	if hard(v1, v2) {
+		addr1 := v1.pointer()
+		addr2 := v2.pointer()
+		if uintptr(addr1) > uintptr(addr2) {
+			// Canonicalize order to reduce number of entries in visited.
+			// Assumes non-moving garbage collector.
+			addr1, addr2 = addr2, addr1
+		}
+
+		// Short circuit if references are already seen.
+		v := visit{addr1, addr2, v1.typecode}
+		if _, ok := visited[v]; ok {
+			return true
+		}
+
+		// Remember for later.
+		visited[v] = struct{}{}
+	}
+
+	switch v1.Kind() {
+	case Array:
+		for i := 0; i < v1.Len(); i++ {
+			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Slice:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		for i := 0; i < v1.Len(); i++ {
+			if !deepValueEqual(v1.Index(i), v2.Index(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Interface:
+		if v1.IsNil() || v2.IsNil() {
+			return v1.IsNil() == v2.IsNil()
+		}
+		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
+	case Ptr:
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		return deepValueEqual(v1.Elem(), v2.Elem(), visited)
+	case Struct:
+		for i, n := 0, v1.NumField(); i < n; i++ {
+			if !deepValueEqual(v1.Field(i), v2.Field(i), visited) {
+				return false
+			}
+		}
+		return true
+	case Map:
+		if v1.IsNil() != v2.IsNil() {
+			return false
+		}
+		if v1.Len() != v2.Len() {
+			return false
+		}
+		if v1.Pointer() == v2.Pointer() {
+			return true
+		}
+		for _, k := range v1.MapKeys() {
+			val1 := v1.MapIndex(k)
+			val2 := v2.MapIndex(k)
+			if !val1.IsValid() || !val2.IsValid() || !deepValueEqual(val1, val2, visited) {
+				return false
+			}
+		}
+		return true
+	case Func:
+		if v1.IsNil() && v2.IsNil() {
+			return true
+		}
+		// Can't do better than this:
+		return false
+	default:
+		// Normal equality suffices
+		return valueInterfaceUnsafe(v1) == valueInterfaceUnsafe(v2)
+	}
+}
+
+// DeepEqual reports whether x and y are ``deeply equal,'' defined as follows.
+// Two values of identical type are deeply equal if one of the following cases applies.
+// Values of distinct types are never deeply equal.
+//
+// Array values are deeply equal when their corresponding elements are deeply equal.
+//
+// Struct values are deeply equal if their corresponding fields,
+// both exported and unexported, are deeply equal.
+//
+// Func values are deeply equal if both are nil; otherwise they are not deeply equal.
+//
+// Interface values are deeply equal if they hold deeply equal concrete values.
+//
+// Map values are deeply equal when all of the following are true:
+// they are both nil or both non-nil, they have the same length,
+// and either they are the same map object or their corresponding keys
+// (matched using Go equality) map to deeply equal values.
+//
+// Pointer values are deeply equal if they are equal using Go's == operator
+// or if they point to deeply equal values.
+//
+// Slice values are deeply equal when all of the following are true:
+// they are both nil or both non-nil, they have the same length,
+// and either they point to the same initial entry of the same underlying array
+// (that is, &x[0] == &y[0]) or their corresponding elements (up to length) are deeply equal.
+// Note that a non-nil empty slice and a nil slice (for example, []byte{} and []byte(nil))
+// are not deeply equal.
+//
+// Other values - numbers, bools, strings, and channels - are deeply equal
+// if they are equal using Go's == operator.
+//
+// In general DeepEqual is a recursive relaxation of Go's == operator.
+// However, this idea is impossible to implement without some inconsistency.
+// Specifically, it is possible for a value to be unequal to itself,
+// either because it is of func type (uncomparable in general)
+// or because it is a floating-point NaN value (not equal to itself in floating-point comparison),
+// or because it is an array, struct, or interface containing
+// such a value.
+// On the other hand, pointer values are always equal to themselves,
+// even if they point at or contain such problematic values,
+// because they compare equal using Go's == operator, and that
+// is a sufficient condition to be deeply equal, regardless of content.
+// DeepEqual has been defined so that the same short-cut applies
+// to slices and maps: if x and y are the same slice or the same map,
+// they are deeply equal regardless of content.
+//
+// As DeepEqual traverses the data values it may find a cycle. The
+// second and subsequent times that DeepEqual compares two pointer
+// values that have been compared before, it treats the values as
+// equal rather than examining the values to which they point.
+// This ensures that DeepEqual terminates.
 func DeepEqual(x, y interface{}) bool {
 	if x == nil || y == nil {
 		return x == y
 	}
-
-	panic("unimplemented: reflect.DeepEqual()")
+	v1 := ValueOf(x)
+	v2 := ValueOf(y)
+	if v1.typecode != v2.typecode {
+		return false
+	}
+	return deepValueEqual(v1, v2, make(map[visit]struct{}))
 }