fix: preserve multiline source expression whitespace

mdl-examples/bug-tests/322-multiline-source-expression-whitespace.mdl

@@ -0,0 +1,61 @@
+-- ============================================================================
+-- Bug #322: Multiline source expression whitespace lost on roundtrip
+-- ============================================================================
+--
+-- Symptom (before fix):
+--   The visitor rebuilt expression strings from parsed expression nodes,
+--   so original line breaks and whitespace inside DECLARE initial values
+--   and LOG template parameters were normalized away. A multiline
+--   `declare $X string = ...` statement that authors had carefully
+--   formatted across several lines came back as a single very long line
+--   after describe → exec → describe. Inter-parameter blank lines in
+--   `LOG ... WITH (...)` were similarly collapsed, making real-world
+--   microflows non-fixpoint and producing noisy `mxcli diff-local` output.
+--
+-- After fix:
+--   Added a `SourceExpr` AST node that wraps an expression with its
+--   original source text. The visitor uses `buildSourceExpression` for
+--   source-sensitive declare/log/while expressions, and the executor
+--   serializes `SourceExpr` through to MDL output so the original
+--   whitespace and line breaks survive every roundtrip.
+--
+-- Usage:
+--   mxcli exec mdl-examples/bug-tests/322-multiline-source-expression-whitespace.mdl -p app.mpr
+--   mxcli -p app.mpr -c "describe microflow BugTest322.MF_MultilineDeclare"
+--   mxcli -p app.mpr -c "describe microflow BugTest322.MF_MultilineLogTemplate"
+--   The describe outputs must keep the multiline shape and must be
+--   fixpoints under describe → exec → describe.
+-- ============================================================================
+
+create module BugTest322;
+
+-- DECLARE initial value spread across several lines with leading `+`. The
+-- describer must preserve the line breaks rather than collapse them onto
+-- one line.
+create microflow BugTest322.MF_MultilineDeclare (
+  $Page: integer,
+  $Token: string
+)
+returns string as $Endpoint
+begin
+  declare $Endpoint string = '/api/v1'
++ '/items?page=' + toString($Page)
++ '&token=' + $Token;
+
+  return $Endpoint;
+end;
+/
+
+-- LOG template parameters separated by a blank line. The newline-only
+-- whitespace between `{1} = toString($Count)` and the next parameter must
+-- survive the roundtrip.
+create microflow BugTest322.MF_MultilineLogTemplate (
+  $Count: integer,
+  $Endpoint: string
+)
+begin
+  log info node 'BugTest322' 'Processed {1} items for {2}' with ({1} = toString($Count)
+
+, {2} = $Endpoint);
+end;
+/

mdl/ast/ast_expression.go

@@ -125,6 +125,15 @@ type IfThenElseExpr struct {
 
 func (e *IfThenElseExpr) isExpression() {}
 
+// SourceExpr preserves original expression source text while keeping the parsed
+// expression tree available for callers that need semantic inspection.
+type SourceExpr struct {
+	Expression Expression
+	Source     string
+}
+
+func (e *SourceExpr) isExpression() {}
+
 // ============================================================================
 // XPath-Specific Expression Types
 // ============================================================================

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

@@ -329,6 +329,15 @@ func (fb *flowBuilder) resolveAssociationPaths(expr ast.Expression) ast.Expressi
 			ThenExpr:  fb.resolveAssociationPaths(e.ThenExpr),
 			ElseExpr:  fb.resolveAssociationPaths(e.ElseExpr),
 		}
+	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 fb.resolveAssociationPaths(e.Expression)
 	default:
 		return expr
 	}
@@ -443,6 +452,8 @@ func unwrapParenCall(expr ast.Expression) *ast.FunctionCallExpr {
 			return e
 		case *ast.ParenExpr:
 			expr = e.Inner
+		case *ast.SourceExpr:
+			expr = e.Expression
 		default:
 			return nil
 		}

mdl/executor/cmd_microflows_helpers.go

@@ -327,6 +327,11 @@ func expressionToString(expr ast.Expression) string {
 		thenStr := expressionToString(e.ThenExpr)
 		elseStr := expressionToString(e.ElseExpr)
 		return "if " + cond + " then " + thenStr + " else " + elseStr
+	case *ast.SourceExpr:
+		if e.Source != "" {
+			return e.Source
+		}
+		return expressionToString(e.Expression)
 	default:
 		return ""
 	}
@@ -379,6 +384,11 @@ func expressionToXPath(expr ast.Expression) string {
 		return expressionToString(expr)
 	case *ast.QualifiedNameExpr:
 		return qualifiedNameToXPath(e)
+	case *ast.SourceExpr:
+		if e.Source != "" {
+			return e.Source
+		}
+		return expressionToXPath(e.Expression)
 	default:
 		// For all other expression types, the standard serialization is correct
 		return expressionToString(expr)