Allow missing nodes in template

When a node can not be found, add a missingNode as a placeholder. When
walking the graph, VisitMissing can customize the behaviour for these
nodes. For typechecking and program evaluation missing nodes are always
an error.

During `GetRequiredPlugins` we do not have the program's config
available to us. Previously we would abort the graph walk as soon as we
hit a missing configuration reference. With this PR, we ignore missing
nodes and continue the walk. This allows us detect plugins configured on
resources.

pkg/pulumiyaml/analyser.go

@@ -1114,6 +1114,12 @@ func (tc *typeCache) typeConfig(r *Runner, node configNode) bool {
 	return true
 }
 
+func (tc *typeCache) typeMissing(r *Runner, node missingNode) bool {
+	ctx := r.newContext(node)
+	ctx.errorf(node.key(), fmt.Sprintf("resource, variable, or config value %q not found", node.key().Value))
+	return false
+}
+
 // Checks for config type compatibility between types A and B, and if B can be assigned to A.
 // Config types are compatible if
 // - They are the same type.
@@ -1186,6 +1192,7 @@ func TypeCheck(r *Runner) (Typing, syntax.Diagnostics) {
 		VisitExpr:     types.typeExpr,
 		VisitVariable: types.typeVariable,
 		VisitConfig:   types.typeConfig,
+		VisitMissing:  types.typeMissing,
 		VisitOutput:   types.typeOutput,
 	})
 
@@ -1197,6 +1204,7 @@ type walker struct {
 	VisitVariable func(r *Runner, node variableNode) bool
 	VisitOutput   func(r *Runner, node ast.PropertyMapEntry) bool
 	VisitResource func(r *Runner, node resourceNode) bool
+	VisitMissing  func(r *Runner, node missingNode) bool
 	VisitExpr     func(*evalContext, ast.Expr) bool
 }
 
@@ -1324,6 +1332,15 @@ func (e walker) EvalResource(r *Runner, node resourceNode) bool {
 	return true
 }
 
+func (e walker) EvalMissing(r *Runner, node missingNode) bool {
+	if e.VisitMissing != nil {
+		if !e.VisitMissing(r, node) {
+			return false
+		}
+	}
+	return true
+}
+
 func (e walker) walkPropertyMap(ctx *evalContext, m ast.PropertyMapDecl) bool {
 	for _, prop := range m.Entries {
 		if !e.walk(ctx, prop.Key) {

pkg/pulumiyaml/run.go

@@ -654,6 +654,7 @@ type Evaluator interface {
 	EvalVariable(r *Runner, node variableNode) bool
 	EvalResource(r *Runner, node resourceNode) bool
 	EvalOutput(r *Runner, node ast.PropertyMapEntry) bool
+	EvalMissing(r *Runner, node missingNode) bool
 }
 
 type programEvaluator struct {
@@ -750,6 +751,11 @@ func (e programEvaluator) EvalResource(r *Runner, node resourceNode) bool {
 	return true
 }
 
+func (e programEvaluator) EvalMissing(r *Runner, node missingNode) bool {
+	e.error(node.key(), fmt.Sprintf("resource, variable, or config value %q not found", node.key().Value))
+	return false
+}
+
 func (e programEvaluator) EvalOutput(r *Runner, node ast.PropertyMapEntry) bool {
 	ctx := r.newContext(node)
 	out, ok := e.registerOutput(node)
@@ -885,6 +891,10 @@ func (r *Runner) Run(e Evaluator) syntax.Diagnostics {
 			if !e.EvalResource(r, kvp) {
 				return returnDiags()
 			}
+		case missingNode:
+			if !e.EvalMissing(r, kvp) {
+				return returnDiags()
+			}
 		}
 	}
 

pkg/pulumiyaml/run_test.go

@@ -2043,6 +2043,46 @@ resources:
 	assert.NoError(t, err)
 }
 
+func TestEvaluateMissingError(t *testing.T) {
+	t.Parallel()
+
+	text := `
+name: test-missing-config-value
+runtime: yaml
+variables:
+  foo: ${someConfigValue}
+`
+	tmpl := yamlTemplate(t, strings.TrimSpace(text))
+	err := pulumi.RunErr(func(ctx *pulumi.Context) error {
+		runner := newRunner(tmpl, newMockPackageMap())
+		err := runner.Evaluate(ctx)
+		assert.Len(t, err, 1)
+		assert.Equal(t, "<stdin>:4,8-8: resource, variable, or config value \"someConfigValue\" not found; ", err.Error())
+		return nil
+	}, pulumi.WithMocks("project", "stack", &testMonitor{}))
+	assert.NoError(t, err)
+}
+
+func TestRunMissingIgnore(t *testing.T) {
+	t.Parallel()
+
+	text := `
+name: test-missing-config-value
+runtime: yaml
+variables:
+  foo: ${someConfigValue}
+`
+	tmpl := yamlTemplate(t, strings.TrimSpace(text))
+	err := pulumi.RunErr(func(ctx *pulumi.Context) error {
+		runner := newRunner(tmpl, newMockPackageMap())
+		err := runner.Run(walker{})
+		assert.Len(t, err, 0)
+		assert.Equal(t, "no diagnostics", err.Error())
+		return nil
+	}, pulumi.WithMocks("project", "stack", &testMonitor{}))
+	assert.NoError(t, err)
+}
+
 func TestResourceWithAlias(t *testing.T) {
 	t.Parallel()
 

pkg/pulumiyaml/sort.go

@@ -75,6 +75,18 @@ func (e configNodeProp) value() interface{} {
 	return e.v.V
 }
 
+type missingNode struct {
+	name *ast.StringExpr
+}
+
+func (e missingNode) key() *ast.StringExpr {
+	return e.name
+}
+
+func (missingNode) valueKind() string {
+	return "missing node"
+}
+
 func topologicallySortedResources(t *ast.TemplateDecl, externalConfig []configNode) ([]graphNode, syntax.Diagnostics) {
 	var diags syntax.Diagnostics
 
@@ -166,11 +178,12 @@ func topologicallySortedResources(t *ast.TemplateDecl, externalConfig []configNo
 
 		e, ok := intermediates[name.Value]
 		if !ok {
-			if e2, ok := intermediates[stripConfigNamespace(t.Name.Value, name.Value)]; ok {
+			s := stripConfigNamespace(t.Name.Value, name.Value)
+			if e2, ok := intermediates[s]; ok {
 				e = e2
 			} else {
-				diags.Extend(ast.ExprError(name, fmt.Sprintf("resource, variable, or config value %q not found", name.Value), ""))
-				return false
+				e = missingNode{name}
+				addIntermediate(name.Value, e)
 			}
 		}
 		kind := e.valueKind()