Misc config loading fixes

The main motivation behind this is simplicity and correctnes, but the new small config library is also faster:

```
BenchmarkDefaultConfigProvider/Viper-16         	  252418	      4546 ns/op	    2720 B/op	      30 allocs/op
BenchmarkDefaultConfigProvider/Custom-16        	  450756	      2651 ns/op	    1008 B/op	       6 allocs/op
```

Fixes #8633
Fixes #8618
Fixes #8630
Updates #8591
Closes #6680
Closes #5192

1 files changed, 87 insertions, 0 deletions

diff --git a/common/maps/params_test.go b/common/maps/params_test.go
index df8cbf8d6..8859bb86b 100644
--- a/common/maps/params_test.go
+++ b/common/maps/params_test.go
@@ -69,3 +69,90 @@ func TestGetNestedParamFnNestedNewKey(t *testing.T) {
 	c.Assert(nestedKey, qt.Equals, "new")
 	c.Assert(owner, qt.DeepEquals, nested)
 }
+
+func TestParamsSetAndMerge(t *testing.T) {
+	c := qt.New(t)
+
+	createParamsPair := func() (Params, Params) {
+		p1 := Params{"a": "av", "c": "cv", "nested": Params{"al2": "al2v", "cl2": "cl2v"}}
+		p2 := Params{"b": "bv", "a": "abv", "nested": Params{"bl2": "bl2v", "al2": "al2bv"}, mergeStrategyKey: ParamsMergeStrategyDeep}
+		return p1, p2
+	}
+
+	p1, p2 := createParamsPair()
+
+	p1.Set(p2)
+
+	c.Assert(p1, qt.DeepEquals, Params{
+		"a": "abv",
+		"c": "cv",
+		"nested": Params{
+			"al2": "al2bv",
+			"cl2": "cl2v",
+			"bl2": "bl2v",
+		},
+		"b":              "bv",
+		mergeStrategyKey: ParamsMergeStrategyDeep,
+	})
+
+	p1, p2 = createParamsPair()
+
+	p1.Merge(p2)
+
+	// Default is to do a shallow merge.
+	c.Assert(p1, qt.DeepEquals, Params{
+		"c": "cv",
+		"nested": Params{
+			"al2": "al2v",
+			"cl2": "cl2v",
+		},
+		"b": "bv",
+		"a": "av",
+	})
+
+	p1, p2 = createParamsPair()
+	p1.SetDefaultMergeStrategy(ParamsMergeStrategyNone)
+	p1.Merge(p2)
+	p1.DeleteMergeStrategy()
+
+	c.Assert(p1, qt.DeepEquals, Params{
+		"a": "av",
+		"c": "cv",
+		"nested": Params{
+			"al2": "al2v",
+			"cl2": "cl2v",
+		},
+	})
+
+	p1, p2 = createParamsPair()
+	p1.SetDefaultMergeStrategy(ParamsMergeStrategyShallow)
+	p1.Merge(p2)
+	p1.DeleteMergeStrategy()
+
+	c.Assert(p1, qt.DeepEquals, Params{
+		"a": "av",
+		"c": "cv",
+		"nested": Params{
+			"al2": "al2v",
+			"cl2": "cl2v",
+		},
+		"b": "bv",
+	})
+
+	p1, p2 = createParamsPair()
+	p1.SetDefaultMergeStrategy(ParamsMergeStrategyDeep)
+	p1.Merge(p2)
+	p1.DeleteMergeStrategy()
+
+	c.Assert(p1, qt.DeepEquals, Params{
+		"nested": Params{
+			"al2": "al2v",
+			"cl2": "cl2v",
+			"bl2": "bl2v",
+		},
+		"b": "bv",
+		"a": "av",
+		"c": "cv",
+	})
+
+}