Create rule S7094: Constant patterns should not be used with type lit…

…erals (type_literal_in_constant_pattern) (#4323)

Co-authored-by: antonioaversa <[email protected]>

rules/S7094/dart/metadata.json

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+{
+  "title": "Constant patterns should not be used with type literals",
+  "type": "BUG",
+  "status": "ready",
+  "remediation": {
+    "func": "Constant\/Issue",
+    "constantCost": "1min"
+  },
+  "tags": [
+    "pitfall"
+  ],
+  "defaultSeverity": "Major",
+  "ruleSpecification": "RSPEC-7094",
+  "sqKey": "S7094",
+  "scope": "All",
+  "defaultQualityProfiles": ["Sonar way"],
+  "quickfix": "unknown",
+  "code": {
+    "impacts": {
+      "RELIABILITY": "HIGH"
+    },
+    "attribute": "LOGICAL"
+  }
+}

rules/S7094/dart/rule.adoc

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+https://dart.dev/language/pattern-types#constant[Constant patterns] should not be used with type literals.
+
+== Why is this an issue?
+
+Using constant patterns with type literals is most likely a mistake.
+
+For example, the following code
+
+[source,dart]
+----
+bool isANumber(Object? o) {
+  if (o case num) { // Checks if `o` is `num`, not if it is a `num`
+    return true;
+  }
+  return false;
+}
+----
+
+will always return `false` for any input *value* of type `num` (as in `isANumber(42)`), and will returns `true` only when the input is the *type* `num` (as in `isANumber(int)`).
+
+This is because a constant pattern compares the value of the provided constant against the value being matched, and not against its type.
+
+The original intent of checking whether an `Object? o` is a `num` or not, should be expressed via a https://dart.dev/language/pattern-types#variable[typed variable pattern]:
+
+[source,dart]
+----
+bool isANumber(Object? o) {
+  if (o case num n) { // Checks if `o` is a `num` and assigns the cast value to n
+    return true;
+  }
+  return false;
+}
+----
+
+If the intent of the code is to only check whether the input is a `num` or not, then the `n` variable is not necessary, and a value discard can be used:
+
+[source,dart]
+----
+bool isANumber(Object? o) {
+  if (o case num _) { // Checks if `o` is a `num`, and discards the cast value
+    return true;
+  }
+  return false;
+}
+----
+
+== How to fix it
+
+Convert the https://dart.dev/language/pattern-types#constant[constant pattern] to a https://dart.dev/language/pattern-types#variable[typed variable pattern] by adding a ``++_++`` (value discard) to the type.
+
+=== Code examples
+
+==== Noncompliant code example
+
+[source,dart,diff-id=1,diff-type=noncompliant]
+----
+bool isANumber(Object? o) {
+  if (o case num) {
+    return true;
+  }
+  return false;
+}
+----
+
+==== Compliant solution
+
+[source,dart,diff-id=1,diff-type=compliant]
+----
+bool isANumber(Object? o) {
+  if (o case num _) {
+    return true;
+  }
+  return false;
+}
+----
+
+== Resources
+
+* Dart Docs - https://dart.dev/tools/linter-rules/type_literal_in_constant_pattern[Dart Linter rule - type_literal_in_constant_pattern]
+* Dart Docs - https://dart.dev/language/pattern-types[Language - Pattern types]
+
+ifdef::env-github,rspecator-view[]
+
+'''
+== Implementation Specification
+(visible only on this page)
+
+=== Message
+
+Use 'TypeName _' instead of a type literal.
+
+=== Highlighting
+
+The type literal: e.g. `num` in `if (o1 case num) { }`.
+
+'''
+== Comments And Links
+(visible only on this page)
+
+endif::env-github,rspecator-view[]

rules/S7094/metadata.json

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+{
+}