Add intention/inspections/quickfix contribution quick notes

docs/contributing.md

@@ -36,6 +36,11 @@ git config --global pull.rebase true
 This will avoid your local repo having too many merge commits
 which will help keep your pull request simple and easy to apply.
 
+## Intention/QuickFix/Inspection
+
+Please read the [Intention/QuickFix/Inspection Quick Notes](intentions_inspections_quickfixes.md) if you are
+going to implement inspection, intention or add a quick fix.
+
 ## Checklist
 
 Before submitting the pull request, make sure that you can say "YES" to each point in this short checklist:

docs/intentions_inspections_quickfixes.md

@@ -0,0 +1,49 @@
+## Intention/QuickFix/Inspection Quick Notes
+
+### Platform
+
+Some general information about writing inspection, intention and quick fixes available in [Code Inspections](
+https://www.jetbrains.org/intellij/sdk/docs/tutorials/code_inspections.html) document.
+
+It's important to know about [PSI](https://www.jetbrains.org/intellij/sdk/docs/basics/architectural_overview/psi.html). 
+
+Some PSI viewer will be extremely useful. It might be built-in [Psi Viewer](https://www.jetbrains.com/help/idea/psi-viewer.html) that is 
+going to be enabled when testing inspections with `IDEA` run configuration (**idea.is.internal=true** must be set to active it in Kotlin 
+project). Alternately, external plugin [PsiViewer](https://plugins.jetbrains.com/plugin/227-psiviewer) can be installed.
+
+### Kotlin Project Specific
+
+- Each inspection should be registered in `plugin-common.xml`. This file is included to `plugin.xml` for all plugins obtained from Kotlin 
+source code. 
+
+- Each inspection should be added with the description. The description file should be named after correspondent inspection class with 
+adding `*.html` extension and removing `Inspection` suffix. (`Some.html` for inspection class `SomeInspection`).
+
+- All inspections should have automatic tests. A default place for such tests is `inspectionsLocal` group (`inspections` group can be 
+used if there are no quick fixes available for the inspection).
+
+- `ProblemHighlightType` should always be `ProblemHighlightType.GENERIC_ERROR_OR_WARNING` or empty (there's a correspondent overload for 
+`ProblemsHolder.registerProblem()`), otherwise, it won't be possible to individually change the desired level in the inspection settings.
+
+- Resolve operations (`analyze`, `resolveToCall`, `resolveToDescriptors`) are considered to be expensive and shouldn't be triggered more 
+often than it's absolutely needed. All possible checks should be applied on PSI or file text before actual resolve. 
+
+-  `resolveToDescriptorIfAny()` / `resolveToCall()` functions can be used if the single descriptor or resolved call is needed. 
+It's better to call `analyze` for obtaining `BindingTrace` and use it for fetching other resolution results when inspection 
+requires multiple resolve calls in a row.
+
+- Prefer `resolveToDescriptorIfAny()` over `resolveToDesciptor()` because of exceptions that are thrown from latter 
+function when descriptor is absent. 
+
+- There shouldn't be PSI elements stored in QuickFix classes (`val psi: PsiElement`) as such elements might be invalidated and can lead 
+to memory leaks. Smart pointer (check `SmartPsiElementPointer` class and `createSmartPointer()` function) can be used when such storage 
+is absolutely necessary. 
+
+- It's possible to obtain `LanguageVersionSettings` directly from `psiElement` with `languageVersionSettings` extension.
+
+- Kotlin project itself can be used for new inspection testing. Build a test plugin with the new inspection included, open another 
+instance of Kotlin project and run inspection on the whole project (`Run Inspection By Name` action). 
+    * Check the execution time and consider performance issues?
+    * Check the memory consumption. 
+    * Check the found problems for false positive.
+    * Try to apply a quick fix and check result.