Default the isEqual flag to true in alertmanager

Solves #2602 - the new version of alertmanager introduces an isEqual
flag to support != matchers in alertmanager silences. Clients set this
to true in the JSON blob sent to the api to indicate a foo=bar matcher,
and to false to indicate foo!=bar. Due to gos unmarshalling, anything
that _doesn't_ include this flag will default to false (i.e. a !=
matcher), so any clients that aren't aware of this flag (such as amtools
before negative matchers and the new api) will not send it, and when you
think you are making a foo=bar matcher, alertmanager will interpret that
as a not equals.

This commit changes the Unmarshaling of the v1matcher struct to default
the IsEqual flag to true, to keep the old behaviour for clients not
setting the flag

Signed-off-by: sinkingpoint <colin@quirl.co.nz>

pkg/labels/matcher.go

@@ -110,7 +110,10 @@ func (m Matcher) MarshalJSON() ([]byte, error) {
 }
 
 func (m *Matcher) UnmarshalJSON(data []byte) error {
-	var v1m apiV1Matcher
+	v1m := apiV1Matcher{
+		IsEqual: true,
+	}
+
 	if err := json.Unmarshal(data, &v1m); err != nil {
 		return err
 	}

pkg/labels/matcher_test.go

@@ -254,4 +254,59 @@ func TestMatcherJSON(t *testing.T) {
 			t.Errorf("Doing Marshal and Unmarshal seems to be losing data; before %#v, after %#v", m, m2)
 		}
 	}
+
+	// Unmarshaling tests - testing that unmarshaling JSON gives expected matchers
+	tests = []struct {
+		name  string
+		op    MatchType
+		value string
+		want  string
+	}{
+		{
+			name:  "foo",
+			op:    MatchEqual,
+			value: "bar",
+			want:  `{"name":"foo","value":"bar","isRegex":false}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchEqual,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":false,"isEqual":true}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchNotEqual,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":false,"isEqual":false}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchRegexp,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":true,"isEqual":true}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchNotRegexp,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":true,"isEqual":false}`,
+		},
+	}
+
+	for _, test := range tests {
+		var m Matcher
+		if err := json.Unmarshal([]byte(test.want), &m); err != nil {
+			t.Fatal(err)
+		}
+
+		m2, err := NewMatcher(test.op, test.name, test.value)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if !cmp(m, *m2) {
+			t.Errorf("Unmarshaling seems to be producing unexpected matchers; got %#v, expected %#v", m, m2)
+		}
+	}
 }