Upstream-Status: Backport [see text]

https://github.com/golong/go.git as of commit 22c1d18a27...
Copy src/internal/godebug from go 1.19 since it does not
exist in 1.17.

Signed-off-by: Joe Slater <joe.slater@windriver.com>
---

--- /dev/null
+++ go/src/internal/godebug/godebug.go
@@ -0,0 +1,34 @@
+// Copyright 2021 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 godebug parses the GODEBUG environment variable.
+package godebug
+
+import "os"
+
+// Get returns the value for the provided GODEBUG key.
+func Get(key string) string {
+	return get(os.Getenv("GODEBUG"), key)
+}
+
+// get returns the value part of key=value in s (a GODEBUG value).
+func get(s, key string) string {
+	for i := 0; i < len(s)-len(key)-1; i++ {
+		if i > 0 && s[i-1] != ',' {
+			continue
+		}
+		afterKey := s[i+len(key):]
+		if afterKey[0] != '=' || s[i:i+len(key)] != key {
+			continue
+		}
+		val := afterKey[1:]
+		for i, b := range val {
+			if b == ',' {
+				return val[:i]
+			}
+		}
+		return val
+	}
+	return ""
+}
--- /dev/null
+++ go/src/internal/godebug/godebug_test.go
@@ -0,0 +1,34 @@
+// Copyright 2021 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 godebug
+
+import "testing"
+
+func TestGet(t *testing.T) {
+	tests := []struct {
+		godebug string
+		key     string
+		want    string
+	}{
+		{"", "", ""},
+		{"", "foo", ""},
+		{"foo=bar", "foo", "bar"},
+		{"foo=bar,after=x", "foo", "bar"},
+		{"before=x,foo=bar,after=x", "foo", "bar"},
+		{"before=x,foo=bar", "foo", "bar"},
+		{",,,foo=bar,,,", "foo", "bar"},
+		{"foodecoy=wrong,foo=bar", "foo", "bar"},
+		{"foo=", "foo", ""},
+		{"foo", "foo", ""},
+		{",foo", "foo", ""},
+		{"foo=bar,baz", "loooooooong", ""},
+	}
+	for _, tt := range tests {
+		got := get(tt.godebug, tt.key)
+		if got != tt.want {
+			t.Errorf("get(%q, %q) = %q; want %q", tt.godebug, tt.key, got, tt.want)
+		}
+	}
+}