Add no-contradiction-with-assertion rule (#319)

Author: RunDevelopment

README.md

@@ -104,6 +104,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
 
 | Rule ID | Description |    |
 |:--------|:------------|:---|
+| [regexp/no-contradiction-with-assertion](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-contradiction-with-assertion.html) | disallow elements that contradict assertions |  |
 | [regexp/no-dupe-disjunctions](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-dupe-disjunctions.html) | disallow duplicate disjunctions | :star: |
 | [regexp/no-empty-alternative](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-empty-alternative.html) | disallow alternatives without elements | :star: |
 | [regexp/no-empty-capturing-group](https://ota-meshi.github.io/eslint-plugin-regexp/rules/no-empty-capturing-group.html) | disallow capturing group that captures empty. | :star: |

docs/rules/README.md

@@ -13,6 +13,7 @@ The rules with the following star :star: are included in the `plugin:regexp/reco
 
 | Rule ID | Description |    |
 |:--------|:------------|:---|
+| [regexp/no-contradiction-with-assertion](./no-contradiction-with-assertion.md) | disallow elements that contradict assertions |  |
 | [regexp/no-dupe-disjunctions](./no-dupe-disjunctions.md) | disallow duplicate disjunctions | :star: |
 | [regexp/no-empty-alternative](./no-empty-alternative.md) | disallow alternatives without elements | :star: |
 | [regexp/no-empty-capturing-group](./no-empty-capturing-group.md) | disallow capturing group that captures empty. | :star: |

docs/rules/no-contradiction-with-assertion.md

@@ -0,0 +1,80 @@
+---
+pageClass: "rule-details"
+sidebarDepth: 0
+title: "regexp/no-contradiction-with-assertion"
+description: "disallow elements that contradict assertions"
+---
+# regexp/no-contradiction-with-assertion
+
+> disallow elements that contradict assertions
+
+- :exclamation: <badge text="This rule has not been released yet." vertical="middle" type="error"> ***This rule has not been released yet.*** </badge>
+
+## :book: Rule Details
+
+This rule reports elements that contradict an assertion. All elements reported by this rule fall into one of two categories:
+
+1. An element/alternative that can never be entered.
+
+    This means that the element is dead code and can be removed. Example:
+
+    <eslint-code-block>
+
+    ```js
+    /* eslint regexp/no-contradiction-with-assertion: "error" */
+
+    var foo = /(?=a)(\w|-)/;
+    var foo = /(?=a)b*a/;
+    ```
+
+    </eslint-code-block>
+
+2. An element that is always entered.
+
+    Right now, only quantifiers with a minimum of 0 are reported in this category. They are contradictory because the minimum of 0 is changed by the assertion to be effectively 1. Example:
+
+    <eslint-code-block>
+
+    ```js
+    /* eslint regexp/no-contradiction-with-assertion: "error" */
+
+    var foo = /a\b-?a/;
+    var foo = /^foo$[\s\S]*?^end foo/m;
+    ```
+
+    </eslint-code-block>
+
+This rule is quite similar to [regexp/no-useless-assertions]. While [regexp/no-useless-assertions] tries to find assertions that contradict the pattern, this rule tries to find parts of the pattern that contradict assertions.
+
+
+<eslint-code-block>
+
+```js
+/* eslint regexp/no-contradiction-with-assertion: "error" */
+
+/* ✓ GOOD */
+var foo = /a\b-a/;
+var foo = /a\ba/; // handled by regexp/no-useless-assertions
+
+/* ✗ BAD */
+var foo = /a\b-?a/;
+var foo = /a\b(a|-)/;
+var foo = /a\ba*-/;
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :books: Further reading
+
+- [regexp/no-useless-assertions]
+
+[regexp/no-useless-assertions]: ./no-useless-assertions.md
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/lib/rules/no-contradiction-with-assertion.ts)
+- [Test source](https://github.com/ota-meshi/eslint-plugin-regexp/blob/master/tests/lib/rules/no-contradiction-with-assertion.ts)