- #5209
- update affected `HtmlHelperValiationSummaryTest` and functional tests
- add `ValidationSummaryTagHelperTest` tests to cover related scenarios
##### Behaviour changes when no errors exist for the model:
###### Tag helper
``` html
<div asp-validation-summary="ModelOnly" class="order"><h3>Oopsie<h3></div>
```
previously generated
``` html
<div class="order validation-summary-errors"><h3>Oopsie</h3><ul><li style="display:none"></li>
</ul></div>
```
and now generates
``` html
<div class="order"><h3>Oopsie</h3></div>
```
###### HTML helper
``` c#
@Html.ValidationSummary(excludePropertyErrors: true, message: "Oopsie")
```
previously generated
``` html
<div class=\"validation-summary-errors\"><span>Oopsie</span>
<ul><li style=\"display:none\"></li>
</ul></div>
```
and now generates nothing (`@HtmlString.Empty`).
- #4116
- generalize rules for `ModelMetadata` creation; minimize metadata changes when Model is updated
- down to a single special case in VDD for `Nullable<T>`
- note existing functional tests did not need to change
- remove `ViewDataDictionary(ViewDataDictionary, object)` constructor; use `new VDD<object>(source, model)`
- allow all `Model` assignments in a view component
- copy-constructed VDD in `ViewComponentContext` previously preserved the source's declared type
nits:
- do not call `virtual SetModel()` method from constructor; now mostly redundant
- logic in copy constructor and `SetModel()` is consistent but different enough to keep code separate
- add some missing doc comments
- fix doc comment property versus type confusion; never need to specify `ViewDataDictionary.` prefix
- fix a few `TemplateBuilder` comments and remove unnecessary `model: null` argument to VDD constructor
- Simplify things that used to rely on HtmlTextWriter. This behavior is
now the default.
- Simplify a whole mess of Razor TextWriter code.
- Integration test for merging of TagHelper buffers back into the 'main'
buffer.