Add simplifiable-Stream-CharSequence-joining.ql

Author: Marcono1234

codeql-custom-queries-java/queries/recommendations/simplifiable-Stream-CharSequence-joining.ql

@@ -0,0 +1,88 @@
+/**
+ * Finds conversion of an array or a `Collection<CharSequence>` to a `Stream`
+ * just to join the elements to a single string. Such code can be simplified
+ * by using `String.join`. For example:
+ * ```java
+ * List<String> words = ...;
+ * String sentence = words.stream().collect(Collectors.joining(" "));
+ *
+ * // Can be simplified as
+ * String sentence = String.join(" ", words);
+ * ```
+ *
+ * @kind problem
+ */
+
+import java
+
+class CollectionStreamMethod extends Method {
+  CollectionStreamMethod() {
+    getDeclaringType().hasQualifiedName("java.util", "Collection") and
+    hasStringSignature("stream()")
+  }
+}
+
+class ArrayAsStreamMethod extends Method {
+  ArrayAsStreamMethod() {
+    isStatic() and
+    (
+      getDeclaringType().hasQualifiedName("java.util", "Arrays") and
+      hasName("stream")
+      or
+      getDeclaringType().hasQualifiedName("java.util.stream", "Stream") and
+      hasName("of")
+    )
+  }
+}
+
+class CollectMethod extends Method {
+  CollectMethod() {
+    getDeclaringType().hasQualifiedName("java.util.stream", "Stream") and
+    hasName("collect")
+  }
+}
+
+class JoiningCollectorMethod extends Method {
+  JoiningCollectorMethod() {
+    getDeclaringType().hasQualifiedName("java.util.stream", "Collectors") and
+    hasName("joining") and
+    // Ignore variant with additional prefix and suffix arguments
+    getNumberOfParameters() = [0, 1]
+  }
+}
+
+from
+  Expr collectionExpr, MethodAccess charSeqStreamExpr, MethodAccess collectCall,
+  MethodAccess joiningCall
+where
+  (
+    exists(MethodAccess collectionStreamCall | charSeqStreamExpr = collectionStreamCall |
+      collectionStreamCall.getQualifier() = collectionExpr and
+      collectionStreamCall.getMethod().getSourceDeclaration().getASourceOverriddenMethod*()
+        instanceof CollectionStreamMethod
+    )
+    or
+    exists(MethodAccess arrayStreamCall | charSeqStreamExpr = arrayStreamCall |
+      arrayStreamCall.getArgument(0) = collectionExpr and
+      arrayStreamCall.getMethod() instanceof ArrayAsStreamMethod
+    )
+  ) and
+  // Has type Stream<CharSequence>
+  charSeqStreamExpr
+      .getType()
+      .(ParameterizedType)
+      .getTypeArgument(0)
+      .getErasure()
+      .(RefType)
+      .getASourceSupertype*()
+      .hasQualifiedName("java.lang", "CharSequence") and
+  // Calls `stream.collect(...)`
+  collectCall.getQualifier() = charSeqStreamExpr and
+  collectCall.getMethod().getSourceDeclaration().getASourceOverriddenMethod*() instanceof
+    CollectMethod and
+  // Calls `collect(Collectors.joining(...))`
+  collectCall.getArgument(0) = joiningCall and
+  joiningCall.getMethod().getSourceDeclaration().getASourceOverriddenMethod*() instanceof
+    JoiningCollectorMethod
+select joiningCall, "Could instead use `String.join` to join elements of $@", collectionExpr,
+  "this collection"