fix: unwrap empty source expressions during association resolution

Symptom: resolveAssociationPaths could return a SourceExpr wrapper with an
empty Source field after resolving the inner expression.

Root cause: the SourceExpr branch rebuilt the wrapper even when there was no
source text to preserve. That made the wrapper semantically redundant and left
future callers dependent on expressionToString peeling it away.

Fix: keep non-empty SourceExpr values verbatim for whitespace-preserving
roundtrips, but unwrap empty SourceExpr values to the resolved inner expression.

Tests: make build; focused SourceExpr association-resolution tests; make test.

Author: hjothamendix

mdl/executor/bugfix_test.go

@@ -515,6 +515,40 @@ func TestResolveAssociationPaths(t *testing.T) {
 	}
 }
 
+func TestResolveAssociationPathsUnwrapsEmptySourceExpr(t *testing.T) {
+	fb := &flowBuilder{}
+	resolved := fb.resolveAssociationPaths(&ast.SourceExpr{
+		Expression: &ast.VariableExpr{Name: "CurrentObject"},
+	})
+
+	if _, ok := resolved.(*ast.SourceExpr); ok {
+		t.Fatalf("empty SourceExpr should unwrap to resolved inner expression, got %T", resolved)
+	}
+	if got := expressionToString(resolved); got != "$CurrentObject" {
+		t.Fatalf("resolved expression = %q, want $CurrentObject", got)
+	}
+}
+
+func TestResolveAssociationPathsKeepsNonEmptySourceExprVerbatim(t *testing.T) {
+	source := "$CurrentObject/Module.Assoc/Name\n"
+	fb := &flowBuilder{}
+	resolved := fb.resolveAssociationPaths(&ast.SourceExpr{
+		Expression: &ast.AttributePathExpr{
+			Variable: "CurrentObject",
+			Path:     []string{"Module.Assoc", "Name"},
+		},
+		Source: source,
+	})
+
+	sourceExpr, ok := resolved.(*ast.SourceExpr)
+	if !ok {
+		t.Fatalf("non-empty SourceExpr should remain SourceExpr, got %T", resolved)
+	}
+	if sourceExpr.Source != source {
+		t.Fatalf("source = %q, want %q", sourceExpr.Source, source)
+	}
+}
+
 // TestExprToStringNoSpaces verifies that association navigation expressions
 // produce no extra spaces around separators after parsing.
 // Issue #120: generated $Order / Module.Assoc / Name instead of $Order/Module.Assoc/Name

mdl/executor/cmd_microflows_builder.go

@@ -331,12 +331,13 @@ func (fb *flowBuilder) resolveAssociationPaths(expr ast.Expression) ast.Expressi
 		}
 	case *ast.SourceExpr:
 		if e.Source != "" {
+			// Non-empty Source is the exact expression text to write back.
+			// Rebuilding it here would defeat the whitespace-preservation
+			// purpose of SourceExpr, so keep the parsed tree only for callers
+			// that need semantic inspection.
 			return e
 		}
-		return &ast.SourceExpr{
-			Expression: fb.resolveAssociationPaths(e.Expression),
-			Source:     e.Source,
-		}
+		return fb.resolveAssociationPaths(e.Expression)
 	default:
 		return expr
 	}