Add UnusedPipeVariableLinter

src/Linters/UnusedPipeVariableLinter.hack

@@ -0,0 +1,39 @@
+/*
+ *  Copyright (c) 2017-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the MIT license found in the
+ *  LICENSE file in the root directory of this source tree.
+ *
+ */
+
+namespace Facebook\HHAST;
+
+final class UnusedPipeVariableLinter extends ASTLinter {
+  const type TConfig = shape();
+  const type TNode = BinaryExpression;
+  const type TContext = Script;
+
+  <<__Override>>
+  public function getLintErrorForNode(
+    Script $_script,
+    BinaryExpression $expr,
+  ): ?ASTLintError {
+    $op = $expr->getOperator();
+    if (!$op is BarGreaterThanToken) {
+      return null;
+    }
+    $rhs = $expr->getRightOperand();
+    $pipe_var = $rhs->getFirstDescendantOfType(PipeVariableExpression::class);
+
+    if ($pipe_var is null) {
+      return new ASTLintError(
+        $this,
+        'Missing pipe variable in right-hand side of pipe operator',
+        $expr,
+      );
+    }
+
+    return null;
+  }
+}

tests/UnusedPipeVariableLinterTest.hack

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+/*
+ *  Copyright (c) 2017-present, Facebook, Inc.
+ *  All rights reserved.
+ *
+ *  This source code is licensed under the MIT license found in the
+ *  LICENSE file in the root directory of this source tree.
+ *
+ */
+
+namespace Facebook\HHAST;
+
+final class UnusedPipeVariableLinterTest extends TestCase {
+  use LinterTestTrait;
+
+  <<__Override>>
+  protected function getLinter(string $file): UnusedPipeVariableLinter {
+    return UnusedPipeVariableLinter::fromPath($file);
+  }
+
+  <<__Override>>
+  public function getCleanExamples(): vec<(string)> {
+    return vec[
+      tuple(
+        '<?hh function foo(): string { return "abc" |> Str\uppercase($$); }',
+      ),
+    ];
+  }
+}

tests/examples/UnusedPipeVariableLinter/unused_pipe.php.expect

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+[
+    {
+        "blame": "  htmlspecialchars($html) |> serialize($html)",
+        "blame_pretty": "  htmlspecialchars($html) |> serialize($html)",
+        "description": "Missing pipe variable in right-hand side of pipe operator"
+    }
+]

tests/examples/UnusedPipeVariableLinter/unused_pipe.php.in

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+<?hh
+
+function unused_pipe(string $html): void {
+  htmlspecialchars($html) |> serialize($html);
+}