Support preserving spew state (seen pointers) across operations and API calls

spew/config.go

@@ -111,6 +111,17 @@ type ConfigState struct {
 	// provides some degree of stability across runs versus
 	// printing out raw pointers. This can consume much memory.
 	UseOrdinals bool
+
+	// Preserve state of a spew (dump, format) operation for use
+	// by the next such operation (including across multiple
+	// arguments to a single API call as well as across API
+	// calls). Currently useful only when NoDuplicates is true.
+	PreserveSpewState bool
+
+	// The state of the last spew (dump, format) operation, if
+	// PreserveSpewState was when that operation was started.
+	// Can be copied to a different ConfigState object.
+	SpewState SpewState
 }
 
 // Config is the active configuration of the top-level functions.

spew/dump.go

@@ -522,10 +522,19 @@ func fdump(cs *ConfigState, w io.Writer, a ...interface{}) {
 		d := dumpState{w: w, cs: cs}
 		d.pointers = make(map[uintptr]int)
 		if cs.NoDuplicates || cs.UseOrdinals {
+			if cs.SpewState.allPointers == nil {
 				d.allPointers = make(map[uintptr]uintptr)
+			} else {
+				d.allPointers = cs.SpewState.allPointers
+			}
 		}
 		d.dump(reflect.ValueOf(arg))
 		d.w.Write(newlineBytes)
+		if d.allPointers != nil { // cs.NoDuplicates || cs.UseOrdinals
+			if cs.PreserveSpewState {
+				cs.SpewState.allPointers = d.allPointers
+			}
+		}
 	}
 }
 

spew/spew.go

@@ -21,6 +21,12 @@ import (
 	"io"
 )
 
+// Wraps the end state of a spew (dump or format) operation for use by
+// the next operation, if so configured.
+type SpewState struct {
+	allPointers map[uintptr]uintptr
+}
+
 // Errorf is a wrapper for fmt.Errorf that treats each argument as if it were
 // passed with a default Formatter interface returned by NewFormatter.  It
 // returns the formatted string as a value that satisfies error.  See