slog: accept UTC times and Windows drive letters

The regexp that matches the current time in tests now accepts a "Z"
timezone designator. Previously it assumed that the timezone was
formatted as an offset from UTC.

The regexp that matched a source pathname now accepts an optional
intial drive letter and colon, for Windows compatibility.

Change-Id: I17dfae16e08cae0291abe90216ed25c61750dffb
Reviewed-on: https://go-review.googlesource.com/c/exp/+/429836
Run-TryBot: Jonathan Amsterdam <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: jba

slog/logger_test.go

@@ -16,7 +16,7 @@ import (
 	"time"
 )
 
-const timeRE = `\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}-\d{2}:\d{2}`
+const timeRE = `\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}\.\d{3}(Z|-\d{2}:\d{2})`
 
 func TestLogTextHandler(t *testing.T) {
 	var buf bytes.Buffer

slog/text_handler_test.go

@@ -97,7 +97,7 @@ func TestTextHandlerSource(t *testing.T) {
 		t.Fatal(err)
 	}
 	got := buf.String()
-	wantRE := `source=[^:]+text_handler_test\.go:\d+ msg`
+	wantRE := `source=([A-Z]:)?[^:]+text_handler_test\.go:\d+ msg`
 	matched, err := regexp.MatchString(wantRE, got)
 	if err != nil {
 		t.Fatal(err)