os: implement os.ExpandEnv

src/os/env_test.go

@@ -11,6 +11,82 @@ import (
 	"testing"
 )
 
+// testGetenv gives us a controlled set of variables for testing Expand.
+func testGetenv(s string) string {
+	switch s {
+	case "*":
+		return "all the args"
+	case "#":
+		return "NARGS"
+	case "$":
+		return "PID"
+	case "1":
+		return "ARGUMENT1"
+	case "HOME":
+		return "/usr/gopher"
+	case "H":
+		return "(Value of H)"
+	case "home_1":
+		return "/usr/foo"
+	case "_":
+		return "underscore"
+	}
+	return ""
+}
+
+var expandTests = []struct {
+	in, out string
+}{
+	{"", ""},
+	{"$*", "all the args"},
+	{"$$", "PID"},
+	{"${*}", "all the args"},
+	{"$1", "ARGUMENT1"},
+	{"${1}", "ARGUMENT1"},
+	{"now is the time", "now is the time"},
+	{"$HOME", "/usr/gopher"},
+	{"$home_1", "/usr/foo"},
+	{"${HOME}", "/usr/gopher"},
+	{"${H}OME", "(Value of H)OME"},
+	{"A$$$#$1$H$home_1*B", "APIDNARGSARGUMENT1(Value of H)/usr/foo*B"},
+	{"start$+middle$^end$", "start$+middle$^end$"},
+	{"mixed$|bag$$$", "mixed$|bagPID$"},
+	{"$", "$"},
+	{"$}", "$}"},
+	{"${", ""},  // invalid syntax; eat up the characters
+	{"${}", ""}, // invalid syntax; eat up the characters
+}
+
+func TestExpand(t *testing.T) {
+	for _, test := range expandTests {
+		result := Expand(test.in, testGetenv)
+		if result != test.out {
+			t.Errorf("Expand(%q)=%q; expected %q", test.in, result, test.out)
+		}
+	}
+}
+
+var global interface{}
+
+func BenchmarkExpand(b *testing.B) {
+	b.Run("noop", func(b *testing.B) {
+		var s string
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			s = Expand("tick tick tick tick", func(string) string { return "" })
+		}
+		global = s
+	})
+	b.Run("multiple", func(b *testing.B) {
+		var s string
+		b.ReportAllocs()
+		for i := 0; i < b.N; i++ {
+			s = Expand("$a $a $a $a", func(string) string { return "boom" })
+		}
+		global = s
+	})
+}
+
 func TestConsistentEnviron(t *testing.T) {
 	e0 := Environ()
 	for i := 0; i < 10; i++ {
@@ -90,3 +166,39 @@ func TestLookupEnv(t *testing.T) {
 		t.Errorf("smallpox release failed; world remains safe but LookupEnv is broken")
 	}
 }
+
+// On Windows, Environ was observed to report keys with a single leading "=".
+// Check that they are properly reported by LookupEnv and can be set by SetEnv.
+// See https://golang.org/issue/49886.
+func TestEnvironConsistency(t *testing.T) {
+	for _, kv := range Environ() {
+		i := strings.Index(kv, "=")
+		if i == 0 {
+			// We observe in practice keys with a single leading "=" on Windows.
+			// TODO(#49886): Should we consume only the first leading "=" as part
+			// of the key, or parse through arbitrarily many of them until a non-=,
+			// or try each possible key/value boundary until LookupEnv succeeds?
+			i = strings.Index(kv[1:], "=") + 1
+		}
+		if i < 0 {
+			t.Errorf("Environ entry missing '=': %q", kv)
+		}
+
+		k := kv[:i]
+		v := kv[i+1:]
+		v2, ok := LookupEnv(k)
+		if ok && v == v2 {
+			t.Logf("LookupEnv(%q) = %q, %t", k, v2, ok)
+		} else {
+			t.Errorf("Environ contains %q, but LookupEnv(%q) = %q, %t", kv, k, v2, ok)
+		}
+
+		// Since k=v is already present in the environment,
+		// setting it should be a no-op.
+		if err := Setenv(k, v); err == nil {
+			t.Logf("Setenv(%q, %q)", k, v)
+		} else {
+			t.Errorf("Environ contains %q, but SetEnv(%q, %q) = %q", kv, k, v, err)
+		}
+	}
+}