Disable XSD validation when xsi:schemaLocation doesn't declare the

namespace for the document element root.

See eclipse-lemminx/lemminx#951

Signed-off-by: azerr <azerr@redhat.com>

Author: angelozerr

README.md

@@ -84,8 +84,8 @@ The following settings are supported:
 * [`xml.codeLens.enabled`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/CodeLens.md): Enable/disable XML CodeLens. Default is `false`.
 * [`xml.preferences.showSchemaDocumentationType`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Preferences.md#documentation-type): Specifies the source of the XML schema documentation displayed on hover and completion. Default is `all`.
 * [`xml.validation.enabled`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Validation.md): Enable/disable all validation. Default is `true`.
-* `xml.validation.schema`: Enable/disable schema based validation. Default is `true`. Ignored if `xml.validation.enabled` is set to `false`
-* [`xml.validation.disallowDocTypeDecl`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Validation.md#disallow-doc-type-declarations): Enable/disable if a fatal error is thrown if the incoming document contains a DOCTYPE declaration. Default is `false`.
+ * [`xml.validation.schema.enabled`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Validation.md#xmlvalidationschemaenabled): Enable/disable schema based validation. Default is `always`. Ignored if [`xml.validation.enabled`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Validation.md) is set to `false`.
+ * [`xml.validation.disallowDocTypeDecl`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Validation.md#disallow-doc-type-declarations): Enable/disable if a fatal error is thrown if the incoming document contains a DOCTYPE declaration. Default is `false`.
 * [`xml.validation.resolveExternalEntities`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Validation.md#resolve-external-entities): Enable/disable resolve of external entities. Default is `false`.
 * [`xml.validation.noGrammar`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Preferences.md#grammar): The message severity when a document has no associated grammar. Defaults to `hint`.
 * [`xml.symbols.enabled`](https://github.com/redhat-developer/vscode-xml/blob/master/docs/Symbols.md#xmlsymbolsenabled): Enable/disable document symbols (Outline). Default is `true`.

docs/Validation.md

@@ -417,3 +417,66 @@ If `xml.validation.resolveExternalEntities` is set to `true` (default is `false`
 Demonstration of the different behaviour:
 
 ![When using the default settings, an external entity that has an XML element as its content will not produce a validation error when nested in an element that expects character content. If `xml.validation.resolveExternalEntities` is enabled, then an error will be produced](./images/Validation/ExternalEntityResolvingDemonstration.gif)
+
+## xml.validation.schema.enabled
+
+The `xml.validation.schema.enabled` gives the capability to enable / disable the validation based on XSD. It can be configured with 3 values:
+
+ * `always`: enable schema based validation.
+ * `never`: disable schema based validation.
+ * `onValidSchema`: enable schema based validation only when the declared xsi:schemaLocation hint or xsi:noNamespaceSchemaLocation is valid for the root element.
+
+To understand the `onValidSchema` settings value, lets go through an example:
+
+Create the XML `foo.xml` file:
+
+```xml
+<foo xmlns="http://foo"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="
+		http://foo foo.xsd">
+	<bar />
+	<BAD_ELEMENT />
+</foo>
+```
+
+Create the XSD `foo.xsd` file (in the same folder as foo.xml) :
+
+```xml
+<?xml version="1.0" encoding="UTF-8"?>
+<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
+  <xs:element name="foo">
+    <xs:complexType>
+      <xs:sequence>
+        <xs:element name="bar" />
+      </xs:sequence>
+    </xs:complexType>
+  </xs:element>
+</xs:schema>
+```
+
+In the XML file, the `BAD_ELEMENT` is higlighted as an error. Update the xsi:schemaLocation with bad namespace hint 
+
+```xml
+<foo>
+...
+	xsi:schemaLocation="
+		http://bad-foo foo.xsd">
+...
+</foo>
+```
+
+In `always` you will have error, in `onValidSchema` you will have none error.
+
+Now, update the xsi:schemaLocation with bad location hint 
+
+```xml
+<foo>
+...
+	xsi:schemaLocation="
+		http://foo bad-foo.xsd">
+...
+</foo>
+```
+
+In `always` you will have error, in `onValidSchema` you will have none error.

package.json

@@ -248,7 +248,7 @@
             "Ignore `xsi:schemaLocation` content formatting."
           ],
           "default": "none",
-          "markdownDescription": "Split `xsi:schemaLocation` content. Default is `none`. Please see [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Formatting%22%2C%22section%22%3A%22xmlformatxsischemalocationsplit%22%7D%5D) for more information",
+          "markdownDescription": "Split `xsi:schemaLocation` content. Default is `none`. See [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Formatting%22%2C%22section%22%3A%22xmlformatxsischemalocationsplit%22%7D%5D) for more information",
           "scope": "window"
         },
         "xml.format.splitAttributes": {
@@ -298,7 +298,7 @@
             "Documentation comes from the `xs:documentation` and `xs:appinfo` elements.",
             "Displays no documentation."
           ],
-          "markdownDescription": "Specifies the source of the XML schema documentation displayed on hover and completion. Default is `all`. Please see [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Preferences%22%2C%22section%22%3A%22documentation-type%22%7D%5D) for more information.",
+          "markdownDescription": "Specifies the source of the XML schema documentation displayed on hover and completion. Default is `all`. See [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Preferences%22%2C%22section%22%3A%22documentation-type%22%7D%5D) for more information.",
           "scope": "window"
         },
         "xml.validation.enabled": {
@@ -307,10 +307,20 @@
           "markdownDescription": "Enable/disable all validation. Default is `true`.",
           "scope": "window"
         },
-        "xml.validation.schema": {
-          "type": "boolean",
-          "default": true,
-          "markdownDescription": "Enable/disable schema based validation. Default is `true`. Ignored if `#xml.validation.enabled#` is set to `false`",
+        "xml.validation.schema.enabled": {
+          "type": "string",
+          "default": "always",
+          "enum": [
+            "always",
+            "never",
+            "onValidSchema"
+          ],
+          "markdownEnumDescriptions": [
+            "Enable schema based validation.",
+            "Disable schema based validation.",
+            "Enable schema based validation only when the declared xsi:schemaLocation hint or xsi:noNamespaceSchemaLocation is valid for the root element."
+          ],
+          "markdownDescription": "Enable/disable schema based validation. Default is `always`. Ignored if `#xml.validation.enabled#` is set to `false`. See [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Validation%22%2C%22section%22%3A%22xmlvalidationschemaenabled%22%7D%5D) for more information.",
           "scope": "window"
         },
         "xml.validation.disallowDocTypeDecl": {
@@ -356,12 +366,12 @@
         "xml.symbols.maxItemsComputed": {
           "type": "integer",
           "default": 5000,
-          "markdownDescription": "The maximum number of outline symbols and folding regions computed (limited for performance reasons). Default is `5000`. Please see [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Symbols%22%2C%22section%22%3A%22xmlsymbolsmaxitemscomputed%22%7D%5D) for more information."
+          "markdownDescription": "The maximum number of outline symbols and folding regions computed (limited for performance reasons). Default is `5000`. See [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Symbols%22%2C%22section%22%3A%22xmlsymbolsmaxitemscomputed%22%7D%5D) for more information."
         },
         "xml.symbols.showReferencedGrammars": {
           "type": "boolean",
           "default": true,
-          "markdownDescription": "Show referenced grammars in the Outline. Default is `true`. Please see [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Symbols%22%2C%22section%22%3A%22xmlsymbolsshowreferencedgrammars%22%7D%5D) for more information.",
+          "markdownDescription": "Show referenced grammars in the Outline. Default is `true`. See [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Symbols%22%2C%22section%22%3A%22xmlsymbolsshowreferencedgrammars%22%7D%5D) for more information.",
           "scope": "window"
         },
         "xml.symbols.filters": {
@@ -405,7 +415,7 @@
         "xml.extension.jars": {
           "type": "array",
           "default": [],
-          "markdownDescription": "An array of paths to JARs that should be contributed to the LemMinX classpath. The paths can include glob patterns. This is intended to be used as a tool for developing extensions to vscode-xml. Please see [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Preferences%22%2C%22section%22%3A%22extension-jars%22%7D%5D) for more information",
+          "markdownDescription": "An array of paths to JARs that should be contributed to the LemMinX classpath. The paths can include glob patterns. This is intended to be used as a tool for developing extensions to vscode-xml. See [here](command:xml.open.docs?%5B%7B%22page%22%3A%22Preferences%22%2C%22section%22%3A%22extension-jars%22%7D%5D) for more information",
           "scope": "window"
         }
       }