Even production tested VB6/ASP code may contain bugs or ambiguities that go unreported on the legacy platform. These "bad source code" problems can cause explicit translation errors or produce undesirable translation results. gmBasic does its best to interpret whatever code you give it, but if there are problems in the source they may lead to problems in .NET. This article describes how to address this in the context of gmStudio upgrade work.
Of course one can always directly modify your source code to correct or improve "bad code", however doing this may cause the source code to diverge from the production code in undocumented or unintentional ways. If the source codes are also being updated for other maintenance, the "bad code fixes" may be lost when you merged changes. The preferred way to make "bad code fixes" to improve translation results is to use the gmBasic Pre-editor.
Use the gmBasic pre-processor
gmBasic has a programmable pre-editor that is fast and precise. It allows migration teams to modify the source code in memory before it is processed for translation. Conceptually speaking, this is a search-and-replace facility. The original source code on disk is not modified.
If you are changing your source solely to prepare it for migration, it is a best practice to make changes "by tool" rather than doing them directly "by hand". Using the preprocessor documents the changes, applies them systematically, and makes them repeatable and trackable. This is particularly important if the source code is under active maintenance outside of the migration effort.
In its simplest form, the preprocessor may be invoked by the Compile/Fix or Refactor/EditFile commands.
1) Compile/Fix/Replace commands may placed in your translation script template or in a ScriptRules file:
<Compile ...> <Fix host="AppUtilities" name="PreEdits"> <Replace status="active" name="vbDouble used twice in same Select"> <OldBlock><![CDATA[ Case vbDecimal, vbCurrency, vbDouble, vbSingle ]]></OldBlock> <NewBlock><![CDATA[ Case vbDecimal, vbCurrency, vbSingle ]]></NewBlock> </Replace> </Fix> ... </Compile>
2) Registry-EditFile commands may be placed in a GlobalSettings file. This is particularly useful for shared files – like #include files with web sites or shared modules in VB6 systems.