stacks: make error message more precise

internal/stacks/stackruntime/internal/stackeval/component.go

@@ -110,7 +110,7 @@ func (c *Component) CheckForEachValue(ctx context.Context, phase EvalPhase) (cty
 			switch {
 
 			case cfg.ForEach != nil:
-				result, moreDiags := evaluateForEachExpr(ctx, cfg.ForEach, phase, c.Stack(ctx))
+				result, moreDiags := evaluateForEachExpr(ctx, cfg.ForEach, phase, c.Stack(ctx), "component")
 				diags = diags.Append(moreDiags)
 				if diags.HasErrors() {
 					return cty.DynamicVal, diags

internal/stacks/stackruntime/internal/stackeval/component_test.go

@@ -182,7 +182,7 @@ func TestComponentCheckInstances(t *testing.T) {
 			gotVal, diags := component.CheckForEachValue(ctx, InspectPhase)
 			assertMatchingDiag(t, diags, func(diag tfdiags.Diagnostic) bool {
 				return (diag.Severity() == tfdiags.Error &&
-					diag.Description().Detail == "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this resource / data source / provider / component.")
+					diag.Description().Detail == "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this component.")
 			})
 			wantVal := cty.DynamicVal // placeholder for invalid result
 			if !wantVal.RawEquals(gotVal) {

internal/stacks/stackruntime/internal/stackeval/for_each.go

@@ -21,7 +21,7 @@ import (
 // The caller might still need to do some further validation or post-processing
 // of the result for concerns that are specific to a particular phase or
 // evaluation context.
-func evaluateForEachExpr(ctx context.Context, expr hcl.Expression, phase EvalPhase, scope ExpressionScope) (ExprResultValue, tfdiags.Diagnostics) {
+func evaluateForEachExpr(ctx context.Context, expr hcl.Expression, phase EvalPhase, scope ExpressionScope, callerDiagName string) (ExprResultValue, tfdiags.Diagnostics) {
 	var diags tfdiags.Diagnostics
 	result, moreDiags := EvalExprAndEvalContext(
 		ctx, expr, phase, scope,
@@ -37,7 +37,7 @@ func evaluateForEachExpr(ctx context.Context, expr hcl.Expression, phase EvalPha
 	ty := result.Value.Type()
 
 	const invalidForEachSummary = "Invalid for_each value"
-	const invalidForEachDetail = "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this resource / data source / provider / component."
+	invalidForEachDetail := fmt.Sprintf("The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this %s.", callerDiagName)
 	const sensitiveForEachDetail = "Sensitive values, or values derived from sensitive values, cannot be used as for_each arguments. If used, the sensitive value could be exposed as a resource instance key."
 	switch {
 	case result.Value.HasMark(marks.Sensitive):

internal/stacks/stackruntime/internal/stackeval/for_each_test.go

@@ -144,7 +144,7 @@ func TestEvaluateForEachExpr(t *testing.T) {
 
 	for name, test := range tests {
 		t.Run(name, func(t *testing.T) {
-			gotResult, diags := evaluateForEachExpr(ctx, test.Expr, PlanPhase, scope)
+			gotResult, diags := evaluateForEachExpr(ctx, test.Expr, PlanPhase, scope, "test")
 			got := gotResult.Value
 
 			if test.WantErr != "" {

internal/stacks/stackruntime/internal/stackeval/provider.go

@@ -118,7 +118,7 @@ func (p *Provider) CheckForEachValue(ctx context.Context, phase EvalPhase) (cty.
 			switch {
 
 			case cfg.ForEach != nil:
-				result, moreDiags := evaluateForEachExpr(ctx, cfg.ForEach, phase, p.Stack(ctx))
+				result, moreDiags := evaluateForEachExpr(ctx, cfg.ForEach, phase, p.Stack(ctx), "provider")
 				diags = diags.Append(moreDiags)
 				if diags.HasErrors() {
 					return cty.DynamicVal, diags

internal/stacks/stackruntime/internal/stackeval/provider_test.go

@@ -171,7 +171,7 @@ func TestProviderCheckInstances(t *testing.T) {
 			gotVal, diags := provider.CheckForEachValue(ctx, InspectPhase)
 			assertMatchingDiag(t, diags, func(diag tfdiags.Diagnostic) bool {
 				return (diag.Severity() == tfdiags.Error &&
-					diag.Description().Detail == "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this resource / data source / provider / component.")
+					diag.Description().Detail == "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this provider.")
 			})
 			wantVal := cty.DynamicVal // placeholder for invalid result
 			if !wantVal.RawEquals(gotVal) {

internal/stacks/stackruntime/internal/stackeval/stack_call.go

@@ -103,7 +103,7 @@ func (c *StackCall) CheckForEachValue(ctx context.Context, phase EvalPhase) (cty
 			switch {
 
 			case cfg.ForEach != nil:
-				result, moreDiags := evaluateForEachExpr(ctx, cfg.ForEach, phase, c.Caller(ctx))
+				result, moreDiags := evaluateForEachExpr(ctx, cfg.ForEach, phase, c.Caller(ctx), "stack")
 				diags = diags.Append(moreDiags)
 				if diags.HasErrors() {
 					return cty.DynamicVal, diags

internal/stacks/stackruntime/internal/stackeval/stack_call_config.go

@@ -115,7 +115,7 @@ func (s *StackCallConfig) validateForEachValueInner(ctx context.Context) (cty.Va
 		return cty.NilVal, diags
 	}
 
-	result, moreDiags := evaluateForEachExpr(ctx, s.config.ForEach, ValidatePhase, s.CallerConfig(ctx))
+	result, moreDiags := evaluateForEachExpr(ctx, s.config.ForEach, ValidatePhase, s.CallerConfig(ctx), "stack")
 	diags = diags.Append(moreDiags)
 	return result.Value, diags
 }

internal/stacks/stackruntime/internal/stackeval/stack_call_test.go

@@ -177,7 +177,7 @@ func TestStackCallCheckInstances(t *testing.T) {
 			gotVal, diags := call.CheckForEachValue(ctx, InspectPhase)
 			assertMatchingDiag(t, diags, func(diag tfdiags.Diagnostic) bool {
 				return (diag.Severity() == tfdiags.Error &&
-					diag.Description().Detail == "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this resource / data source / provider / component.")
+					diag.Description().Detail == "The for_each expression must produce either a map of any type or a set of strings. The keys of the map or the set elements will serve as unique identifiers for multiple instances of this stack.")
 			})
 			wantVal := cty.DynamicVal // placeholder for invalid result
 			if !wantVal.RawEquals(gotVal) {