log/slog: generate valid JSON string with empty attributes in Groups

Fixes #62152

Change-Id: I1f76ab26eae3a44292ebe6003006258d5e31d50f
Reviewed-on: https://go-review.googlesource.com/c/go/+/521135
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Andy Pan <panjf2000@gmail.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

diff --git a/src/log/slog/handler.go b/src/log/slog/handler.go
index 369b0a384e1dfcbe349fc8212d27547711052a82..16044f44c6d95565cddf9f045f6bc7411ee908e7 100644 (file)
--- a/src/log/slog/handler.go
+++ b/src/log/slog/handler.go
@@ -233,8 +233,11 @@ func (h *commonHandler) withAttrs(as []Attr) *commonHandler {
        state := h2.newHandleState((*buffer.Buffer)(&h2.preformattedAttrs), false, "")
        defer state.free()
        state.prefix.WriteString(h.groupPrefix)
-       if len(h2.preformattedAttrs) > 0 {
+       if pfa := h2.preformattedAttrs; len(pfa) > 0 {
                state.sep = h.attrSep()
+               if h2.json && pfa[len(pfa)-1] == '{' {
+                       state.sep = ""
+               }
        }
        state.openGroups()
        for _, a := range as {
@@ -310,10 +313,13 @@ func (h *commonHandler) handle(r Record) error {
 
 func (s *handleState) appendNonBuiltIns(r Record) {
        // preformatted Attrs
-       if len(s.h.preformattedAttrs) > 0 {
+       if pfa := s.h.preformattedAttrs; len(pfa) > 0 {
                s.buf.WriteString(s.sep)
-               s.buf.Write(s.h.preformattedAttrs)
+               s.buf.Write(pfa)
                s.sep = s.h.attrSep()
+               if s.h.json && pfa[len(pfa)-1] == '{' {
+                       s.sep = ""
+               }
        }
        // Attrs in Record -- unlike the built-in ones, they are in groups started
        // from WithGroup.

diff --git a/src/log/slog/handler_test.go b/src/log/slog/handler_test.go
index 21c31929b12cb983cf4348ed7769064a3ced0096..4ffd74a495370b43f2642e223f525be237f6dcef 100644 (file)
--- a/src/log/slog/handler_test.go
+++ b/src/log/slog/handler_test.go
@@ -435,6 +435,62 @@ func TestJSONAndTextHandlers(t *testing.T) {
                        wantText: `time.mins=3 time.secs=2 msg=message`,
                        wantJSON: `{"time":{"mins":3,"secs":2},"msg":"message"}`,
                },
+               {
+                       name: "replace empty 1",
+                       with: func(h Handler) Handler {
+                               return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)})
+                       },
+                       replace:  func([]string, Attr) Attr { return Attr{} },
+                       attrs:    []Attr{Group("h", Int("b", 2))},
+                       wantText: "",
+                       wantJSON: `{"g":{"h":{}}}`,
+               },
+               {
+                       name: "replace empty 2",
+                       with: func(h Handler) Handler {
+                               return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
+                       },
+                       replace:  func([]string, Attr) Attr { return Attr{} },
+                       attrs:    []Attr{Group("i", Int("c", 3))},
+                       wantText: "",
+                       wantJSON: `{"g":{"h":{"i":{}}}}`,
+               },
+               {
+                       name: "replace partial empty attrs 1",
+                       with: func(h Handler) Handler {
+                               return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
+                       },
+                       replace: func(groups []string, attr Attr) Attr {
+                               return removeKeys(TimeKey, LevelKey, MessageKey, "a")(groups, attr)
+                       },
+                       attrs:    []Attr{Group("i", Int("c", 3))},
+                       wantText: "g.h.b=2 g.h.i.c=3",
+                       wantJSON: `{"g":{"h":{"b":2,"i":{"c":3}}}}`,
+               },
+               {
+                       name: "replace partial empty attrs 2",
+                       with: func(h Handler) Handler {
+                               return h.WithGroup("g").WithAttrs([]Attr{Int("a", 1)}).WithAttrs([]Attr{Int("n", 4)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
+                       },
+                       replace: func(groups []string, attr Attr) Attr {
+                               return removeKeys(TimeKey, LevelKey, MessageKey, "a", "b")(groups, attr)
+                       },
+                       attrs:    []Attr{Group("i", Int("c", 3))},
+                       wantText: "g.n=4 g.h.i.c=3",
+                       wantJSON: `{"g":{"n":4,"h":{"i":{"c":3}}}}`,
+               },
+               {
+                       name: "replace partial empty attrs 3",
+                       with: func(h Handler) Handler {
+                               return h.WithGroup("g").WithAttrs([]Attr{Int("x", 0)}).WithAttrs([]Attr{Int("a", 1)}).WithAttrs([]Attr{Int("n", 4)}).WithGroup("h").WithAttrs([]Attr{Int("b", 2)})
+                       },
+                       replace: func(groups []string, attr Attr) Attr {
+                               return removeKeys(TimeKey, LevelKey, MessageKey, "a", "c")(groups, attr)
+                       },
+                       attrs:    []Attr{Group("i", Int("c", 3))},
+                       wantText: "g.x=0 g.n=4 g.h.b=2",
+                       wantJSON: `{"g":{"x":0,"n":4,"h":{"b":2,"i":{}}}}`,
+               },
        } {
                r := NewRecord(testTime, LevelInfo, "message", callerPC(2))
                line := strconv.Itoa(r.source().Line)