constraints: remove package

It has moved to golang.org/x/exp/constraints. Perhaps it will move
back to the standard library in a future release.

For #45458
Fixes #50792

Change-Id: I93aa251a7afe7b329a3d3faadc0c5d6388b1f0e9
Reviewed-on: https://go-review.googlesource.com/c/go/+/382460
Trust: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: ianlancetaylor

api/go1.18.txt

@@ -1,12 +1,6 @@
 pkg bufio, method (*Writer) AvailableBuffer() []uint8
 pkg bufio, method (ReadWriter) AvailableBuffer() []uint8
 pkg bytes, func Cut([]uint8, []uint8) ([]uint8, []uint8, bool)
-pkg constraints, type Complex interface {}
-pkg constraints, type Float interface {}
-pkg constraints, type Integer interface {}
-pkg constraints, type Ordered interface {}
-pkg constraints, type Signed interface {}
-pkg constraints, type Unsigned interface {}
 pkg crypto/tls, method (*Conn) NetConn() net.Conn
 pkg debug/buildinfo, func Read(io.ReaderAt) (*debug.BuildInfo, error)
 pkg debug/buildinfo, func ReadFile(string) (*debug.BuildInfo, error)

doc/go1.18.html

@@ -467,14 +467,6 @@ <h2 id="linker">Linker</h2>
 
 <h2 id="library">Core library</h2>
 
-<h3 id="constraints">New <code>constraints</code> package</h3>
-
-<p><!-- CL 349709 -->
-  The new <a href="/pkg/constraints/"><code>constraints</code></a> package
-  defines a set of useful constraints that can be used with type parameters of
-  generic functions.
-</p>
-
 <h3 id="debug/buildinfo">New <code>debug/buildinfo</code> package</h3>
 
 <p><!-- golang.org/issue/39301 -->

src/cmd/compile/internal/types2/testdata/fixedbugs/issue47818.go2

@@ -8,8 +8,6 @@
 
 package go1_17
 
-import "constraints"
-
 type T[P /* ERROR type parameters require go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ] struct{}
 
 // for init (and main, but we're not in package main) we should only get one error
@@ -57,5 +55,3 @@ type (
 	_ = C1
 	_ = C2
 )
-
-type Ordered constraints /* ERROR using type constraint constraints\.Ordered requires go1\.18 or later */ .Ordered

src/cmd/compile/internal/types2/testdata/fixedbugs/issue49705.go2

@@ -4,8 +4,11 @@
 
 package p
 
-import "constraints"
+type Integer interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+	~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr
+}
 
-func shl[I constraints.Integer](n int) I {
+func shl[I Integer](n int) I {
 	return 1 << n
 }

src/constraints/constraints.go

@@ -8,8 +8,6 @@
 
 package go1_17
 
-import "constraints"
-
 type T[P /* ERROR type parameters require go1\.18 or later */ any /* ERROR undeclared name: any \(requires version go1\.18 or later\) */ ] struct{}
 
 // for init (and main, but we're not in package main) we should only get one error
@@ -57,5 +55,3 @@ type (
 	_ = C1
 	_ = C2
 )
-
-type Ordered constraints /* ERROR using type constraint constraints\.Ordered requires go1\.18 or later */ .Ordered

src/constraints/constraints_test.go

@@ -4,8 +4,11 @@
 
 package p
 
-import "constraints"
+type Integer interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+	~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr
+}
 
-func shl[I constraints.Integer](n int) I {
+func shl[I Integer](n int) I {
 	return 1 << n
 }

src/go/types/testdata/fixedbugs/issue47818.go2

@@ -5,11 +5,15 @@
 package a
 
 import (
-	"constraints"
 	"math/rand"
 )
 
-type Builder[T constraints.Integer] struct{}
+type Integer interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+	~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr
+}
+
+type Builder[T Integer] struct{}
 
 func (r Builder[T]) New() T {
 	return T(rand.Int())

src/go/types/testdata/fixedbugs/issue49705.go2

@@ -4,11 +4,12 @@
 
 package a
 
-import (
-	"constraints"
-)
+type Integer interface {
+	~int | ~int8 | ~int16 | ~int32 | ~int64 |
+	~uint | ~uint8 | ~uint16 | ~uint32 | ~uint64 | ~uintptr
+}
 
-type Builder[T constraints.Integer] struct{}
+type Builder[T Integer] struct{}
 
 func (r Builder[T]) New() T {
 	return T(42)

test/typeparam/issue50121.dir/a.go

@@ -7,17 +7,20 @@
 package main
 
 import (
-	"constraints"
 	"fmt"
 )
 
-func zero[T constraints.Complex]() T {
+type Complex interface {
+	~complex64 | ~complex128
+}
+
+func zero[T Complex]() T {
 	return T(0)
 }
-func pi[T constraints.Complex]() T {
+func pi[T Complex]() T {
 	return T(3.14)
 }
-func sqrtN1[T constraints.Complex]() T {
+func sqrtN1[T Complex]() T {
 	return T(-1i)
 }