Merge scope hierarchy for evaluation

internal/runtime/internal/controller/value_cache.go

@@ -199,6 +199,17 @@ func (vc *valueCache) BuildContext() *vm.Scope {
 		}
 	}
 
+	// The syntax pkg only checks the first key when choosing the scope to evaluate an expression.
+	// if you have:
+	// - parent: "test": "component1": v
+	// - child: "test": "component2": v
+	// the expression "test.component1.v" would result in an error because it would use the child scope.
+	// To avoid such conflict, we merge the scopes into one:
+	// - parent: nil
+	// - child: "test": {"component1": v, "component2": v}
+	scope.Variables = mergeScopes(scope)
+	scope.Parent = nil
+
 	return scope
 }
 
@@ -234,3 +245,49 @@ func (vc *valueCache) buildValue(from []ComponentID, offset int) interface{} {
 	}
 	return attrs
 }
+
+// mergeScopes merges the Variables maps of the scope hierarchy into a new map.
+// The child always overrides the parent's value.
+func mergeScopes(scope *vm.Scope) map[string]any {
+	merged := make(map[string]any)
+
+	var mergeFrom func(*vm.Scope)
+	mergeFrom = func(s *vm.Scope) {
+		if s == nil {
+			return
+		}
+		mergeFrom(s.Parent)
+		for k, v := range s.Variables {
+			if pm, ok1 := merged[k].(map[string]any); ok1 {
+				if cm, ok2 := v.(map[string]any); ok2 {
+					merged[k] = mergeNestedMaps(pm, cm)
+					continue
+				}
+			}
+			merged[k] = v
+		}
+	}
+
+	mergeFrom(scope)
+	return merged
+}
+
+func mergeNestedMaps(parent, child map[string]any) map[string]any {
+	merged := make(map[string]any)
+
+	for k, v := range parent {
+		merged[k] = v
+	}
+
+	for k, v := range child {
+		if pm, ok1 := merged[k].(map[string]any); ok1 {
+			if cm, ok2 := v.(map[string]any); ok2 {
+				merged[k] = mergeNestedMaps(pm, cm)
+				continue
+			}
+		}
+		merged[k] = v
+	}
+
+	return merged
+}

internal/runtime/internal/controller/value_cache_test.go

@@ -3,6 +3,7 @@ package controller
 import (
 	"testing"
 
+	"github.com/grafana/alloy/syntax/vm"
 	"github.com/stretchr/testify/require"
 )
 
@@ -174,3 +175,119 @@ func TestModuleArgumentCache(t *testing.T) {
 		})
 	}
 }
+
+func TestScopeMerge(t *testing.T) {
+	vc := newValueCache()
+	scope := vm.NewScope(
+		map[string]any{
+			"test": map[string]any{
+				"scope": barArgs{Number: 13},
+			},
+		},
+	)
+	vc.SetScope(scope)
+	vc.CacheExports(ComponentID{"foo", "bar"}, barArgs{Number: 12})
+	res := vc.BuildContext()
+
+	expected := map[string]any{
+		"test": map[string]any{
+			"scope": barArgs{
+				Number: 13,
+			},
+		},
+		"foo": map[string]any{
+			"bar": barArgs{
+				Number: 12,
+			},
+		},
+	}
+	require.Equal(t, expected, res.Variables)
+}
+
+func TestScopeMergeConflict(t *testing.T) {
+	vc := newValueCache()
+	scope := vm.NewScope(
+		map[string]any{
+			"test": map[string]any{
+				"scope": barArgs{Number: 13},
+			},
+		},
+	)
+	vc.SetScope(scope)
+	vc.CacheExports(ComponentID{"test", "bar"}, barArgs{Number: 12})
+	res := vc.BuildContext()
+
+	expected := map[string]any{
+		"test": map[string]any{
+			"scope": barArgs{
+				Number: 13,
+			},
+			"bar": barArgs{
+				Number: 12,
+			},
+		},
+	}
+	require.Equal(t, expected, res.Variables)
+}
+
+func TestScopeMergeOverride(t *testing.T) {
+	vc := newValueCache()
+	scope := vm.NewScope(
+		map[string]any{
+			"test": map[string]any{
+				"scope": barArgs{Number: 13},
+			},
+		},
+	)
+	vc.SetScope(scope)
+	vc.CacheExports(ComponentID{"test", "scope"}, barArgs{Number: 12})
+	res := vc.BuildContext()
+
+	expected := map[string]any{
+		"test": map[string]any{
+			"scope": barArgs{
+				Number: 12,
+			},
+		},
+	}
+	require.Equal(t, expected, res.Variables)
+}
+
+func TestScopeMergeMoreNesting(t *testing.T) {
+	vc := newValueCache()
+	parentScope := vm.NewScope(
+		map[string]any{
+			"test": map[string]any{
+				"cp1": map[string]any{
+					"scope": barArgs{Number: 13},
+				},
+			},
+		},
+	)
+	scope := vm.NewScopeWithParent(
+		parentScope,
+		map[string]any{
+			"test": map[string]any{
+				"cp2": barArgs{Number: 12},
+			},
+		},
+	)
+	vc.SetScope(scope)
+	vc.CacheExports(ComponentID{"test", "cp1", "foo"}, barArgs{Number: 12})
+	vc.CacheExports(ComponentID{"test", "cp1", "bar", "fizz"}, barArgs{Number: 2})
+	res := vc.BuildContext()
+
+	expected := map[string]any{
+		"test": map[string]any{
+			"cp1": map[string]any{
+				"scope": barArgs{Number: 13},
+				"foo":   barArgs{Number: 12},
+				"bar": map[string]any{
+					"fizz": barArgs{Number: 2},
+				},
+			},
+			"cp2": barArgs{Number: 12},
+		},
+	}
+	require.Equal(t, expected, res.Variables)
+}