Drop support for Go 1.20 (#4967)

* Update README.md

* Remove 1.20 support from CI workflows

* Update all go mod

* Add changelog entry

* Update go mod tidy target

* Run go mod tidy

* Replace sliceEqualFunc with slices.EqualFunc

* Replace grow with slices.Grow

* Replace ensureAttributesCapacity with slices.Grow

* Replace conditional with min

* Use slices module for slice comparison in metricdatatest

log/go.mod

@@ -1,6 +1,6 @@
 module go.opentelemetry.io/otel/log
 
-go 1.20
+go 1.21
 
 require (
 	github.com/go-logr/logr v1.4.1

log/go.sum

@@ -6,6 +6,7 @@ github.com/go-logr/logr v1.4.1/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ4
 github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
 github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
+github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.8.4 h1:CcVxjf3Q8PM0mHUKJCdn+eZZtm5yQwehR5yeSVQQcUk=

log/keyvalue.go

@@ -20,6 +20,7 @@ import (
 	"bytes"
 	"errors"
 	"math"
+	"slices"
 	"unsafe"
 
 	"go.opentelemetry.io/otel/internal/global"
@@ -261,11 +262,9 @@ func (v Value) Equal(w Value) bool {
 	case KindFloat64:
 		return v.asFloat64() == w.asFloat64()
 	case KindSlice:
-		// TODO: replace with slices.EqualFunc when Go 1.20 support dropped.
-		return sliceEqualFunc(v.asSlice(), w.asSlice(), Value.Equal)
+		return slices.EqualFunc(v.asSlice(), w.asSlice(), Value.Equal)
 	case KindMap:
-		// TODO: replace with slices.EqualFunc when Go 1.20 support dropped.
-		return sliceEqualFunc(v.asMap(), w.asMap(), KeyValue.Equal)
+		return slices.EqualFunc(v.asMap(), w.asMap(), KeyValue.Equal)
 	case KindBytes:
 		return bytes.Equal(v.asBytes(), w.asBytes())
 	case KindEmpty:
@@ -276,30 +275,6 @@ func (v Value) Equal(w Value) bool {
 	}
 }
 
-// sliceEqualFunc reports whether two slices are equal using an equality
-// function on each pair of elements. If the lengths are different,
-// sliceEqualFunc returns false. Otherwise, the elements are compared in
-// increasing index order, and the comparison stops at the first index for
-// which eq returns false.
-//
-// This is based on [EqualFunc]. It was added to provide backwards
-// compatibility for Go 1.20. When Go 1.20 is no longer supported it can be
-// removed.
-//
-// EqualFunc: https://pkg.go.dev/slices#EqualFunc
-func sliceEqualFunc[T any](s1 []T, s2 []T, eq func(T, T) bool) bool {
-	if len(s1) != len(s2) {
-		return false
-	}
-	for i, v1 := range s1 {
-		v2 := s2[i]
-		if !eq(v1, v2) {
-			return false
-		}
-	}
-	return true
-}
-
 // An KeyValue is a key-value pair used to represent a log attribute (a
 // superset of [go.opentelemetry.io/otel/attribute.KeyValue]) and map item.
 type KeyValue struct {

log/record.go

@@ -14,7 +14,10 @@
 
 package log // import "go.opentelemetry.io/otel/log"
 
-import "time"
+import (
+	"slices"
+	"time"
+)
 
 // attributesInlineCount is the number of attributes that are efficiently
 // stored in an array within a Record. This value is borrowed from slog which
@@ -125,26 +128,10 @@ func (r *Record) AddAttributes(attrs ...KeyValue) {
 		r.nFront++
 	}
 
-	// TODO: when Go 1.20 is no longer supported, use slices.Grow instead.
-	r.back = grow(r.back, len(attrs[i:]))
+	r.back = slices.Grow(r.back, len(attrs[i:]))
 	r.back = append(r.back, attrs[i:]...)
 }
 
-// grow increases the slice's capacity, if necessary, to guarantee space for
-// another n elements. After grow(n), at least n elements can be appended to
-// the slice without another allocation.
-//
-// This is based on [Grow]. It is not available in Go 1.20 so it is reproduced
-// here.
-//
-// [Grow]: https://pkg.go.dev/slices#Grow
-func grow(slice []KeyValue, n int) []KeyValue {
-	if n -= cap(slice) - len(slice); n > 0 {
-		slice = append(slice[:cap(slice)], make([]KeyValue, n)...)[:len(slice)]
-	}
-	return slice
-}
-
 // AttributesLen returns the number of attributes in the log record.
 func (r *Record) AttributesLen() int {
 	return r.nFront + len(r.back)