[flang] [llvm] [flang/flang-rt] Implement show_descriptor intrinsic, a non-standard extension. (PR #170389)

[Slava Zakharin via llvm-commits]

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@@ -158,3 +159,125 @@ TEST(Descriptor, FixedStride) {
   EXPECT_TRUE(descriptor.IsContiguous());
   EXPECT_EQ(descriptor.FixedStride().value_or(-666), 0);
 }
+
+// The test below uses file operations that have nuances across multiple
+// platforms. Hence limit coverage by linux only unless wider coverage
+// should be required.
+#if defined(__linux__) && !defined(__ANDROID__)
+TEST(Descriptor, Dump) {
+  StaticDescriptor<4> staticDesc[2];
+  Descriptor &descriptor{staticDesc[0].descriptor()};
+  using Type = std::int32_t;
+  Type data[8][8][8];
+  constexpr int four{static_cast<int>(sizeof data[0][0][0])};
+  TypeCode integer{TypeCategory::Integer, four};
+  // Scalar
+  descriptor.Establish(integer, four, data, 0);
+  FILE *tmpf = nullptr;
----------------
vzakhari wrote:

```suggestion
  FILE *tmpf{nullptr};
```

https://github.com/llvm/llvm-project/pull/170389