[PATCH] c: Silently ignore pragma region [PR85487]

[Austin Morton]

#pragma region is a feature introduced by Microsoft in order to allow
manual grouping and folding of code within Visual Studio.  It is
entirely ignored by the compiler.  Clang has supported this feature
since 2012 when in MSVC compatibility mode, and enabled it across the
board 3 months ago.

As it stands, you cannot use #pragma region within GCC without
disabling unknown pragma warnings, which is not advisable.

I propose GCC adopt "#pragma region" and "#pragma endregion" in order
to alleviate these issues.  Because the pragma has no purpose at
compile time, the implementation is trivial.


Microsoft Documentation on the feature:
https://docs.microsoft.com/en-us/cpp/preprocessor/region-endregion

LLVM change which enabled pragma region across the board:
https://reviews.llvm.org/D42248

---
 gcc/c-family/ChangeLog               |  5 +++++
 gcc/c-family/c-pragma.c              | 10 ++++++++++
 gcc/testsuite/ChangeLog              |  5 +++++
 gcc/testsuite/gcc.dg/pragma-region.c | 21 +++++++++++++++++++++
 4 files changed, 41 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pragma-region.c

diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index 1eaa99f31..97ba259cd 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,8 @@
+2020-08-27  Austin Morton  <austinpmorton@gmail.com>
+
+ PR c/85487
+ * c-pragma.c (handle_pragma_region): Declare.
+
 2020-08-11  Jakub Jelinek  <jakub@redhat.com>

  PR c/96545
diff --git a/gcc/c-family/c-pragma.c b/gcc/c-family/c-pragma.c
index e3169e68f..de0411d07 100644
--- a/gcc/c-family/c-pragma.c
+++ b/gcc/c-family/c-pragma.c
@@ -1166,6 +1166,13 @@ handle_pragma_message (cpp_reader *ARG_UNUSED(dummy))
     TREE_STRING_POINTER (message));
 }

+/* Silently ignore region pragmas.  */
+
+static void
+handle_pragma_region (cpp_reader *ARG_UNUSED(dummy))
+{
+}
+
 /* Mark whether the current location is valid for a STDC pragma.  */

 static bool valid_location_for_stdc_pragma;
@@ -1584,6 +1591,9 @@ init_pragma (void)

   c_register_pragma_with_expansion (0, "message", handle_pragma_message);

+  c_register_pragma (0, "region", handle_pragma_region);
+  c_register_pragma (0, "endregion", handle_pragma_region);
+
 #ifdef REGISTER_TARGET_PRAGMAS
   REGISTER_TARGET_PRAGMAS ();
 #endif
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 5c1a45716..4033c111c 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2020-08-27  Austin Morton  <austinpmorton@gmail.com>
+
+ PR c/85487
+ * gcc.dg/pragma-region.c: New test.
+
 2020-08-26  Jeff Law  <law@redhat.com>

  * gcc.target/i386/387-7.c: Add dg-require-effective-target c99_runtime.
diff --git a/gcc/testsuite/gcc.dg/pragma-region.c
b/gcc/testsuite/gcc.dg/pragma-region.c
new file mode 100644
index 000000000..72cc2c144
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pragma-region.c
@@ -0,0 +1,21 @@
+/* Verify #pragma region and #pragma endregion do not emit warnings.  */
+
+/* { dg-options "-Wunknown-pragmas" } */
+
+#pragma region
+
+#pragma region name
+
+#pragma region "name"
+
+#pragma region()
+
+#pragma region("name")
+
+#pragma endregion
+
+#pragma endregion garbage
+
+#pragma endregion()
+
+#pragma endregion("garbage")
-- 
2.17.1