PrmPkg: Replace include guards with #pragma once

Replace traditional `#ifndef`/`#define`/`#endif` include guards with
`#pragma` once.

`#pragma once` is a widely supported preprocessor directive that
prevents header files from being included multiple times. It is
supported by all toolchains used to build edk2: GCC, Clang/LLVM, and
MSVC.

Compared to macro-based include guards, `#pragma once`:

- Eliminates the risk of macro name collisions or copy/paste errors
  where two headers inadvertently use the same guard macro.
- Eliminate inconsistency in the way include guard macros are named
  (e.g., some files use `__FILE_H__`, others use `FILE_H_`, etc.).
- Reduces boilerplate (three lines replaced by one).
- Avoids polluting the macro namespace with guard symbols.
- Can improve build times as the preprocessor can skip re-opening the
  file entirely, rather than re-reading it to find the matching
  `#endif` ("multiple-include optimization").
  - Note that some compilers may already optimize traditional include
    guards, by recognzining the idiomatic pattern.

This change is made acknowledging that overall portability of the
code will technically be reduced, as `#pragma once` is not part of the
C/C++ standards.

However, this is considered acceptable given:

1. edk2 already defines a subset of supported compilers in
   BaseTools/Conf/tools_def.template, all of which have supported
   `#pragma once` for over two decades.
2. There have been concerns raised to the project about inconsistent
   include guard naming and potential macro collisions.

Approximate compiler support dates:

- MSVC: Supported since Visual C++ 4.2 (1996)
- GCC: Supported since 3.4 (2004)
  (http://gnu.ist.utl.pt/software/gcc/gcc-3.4/changes.html)
- Clang (LLVM based): Since initial release in 2007

Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>

PrmPkg/Application/PrmInfo/PrmInfo.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef PRM_INFO_H_
-#define PRM_INFO_H_
+#pragma once
 
 #include <Base.h>
 #include <Prm.h>
@@ -45,5 +44,3 @@ typedef struct {
 #define ONE_MICROSECOND  (1000)
 #define ONE_MILLISECOND  (1000 * ONE_MICROSECOND)
 #define ONE_SECOND       (1000 * ONE_MILLISECOND)
-
-#endif

PrmPkg/Include/Library/PrmContextBufferLib.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_CONTEXT_BUFFER_LIB_H_
-#define PRM_CONTEXT_BUFFER_LIB_H_
+#pragma once
 
 #include <Base.h>
 #include <PrmContextBuffer.h>
@@ -95,5 +94,3 @@ GetContextBuffer (
   IN  CONST PRM_MODULE_CONTEXT_BUFFERS  *PrmModuleContextBuffers  OPTIONAL,
   OUT CONST PRM_CONTEXT_BUFFER          **PrmContextBuffer
   );
-
-#endif

PrmPkg/Include/Library/PrmModuleDiscoveryLib.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_MODULE_DISCOVERY_LIB_H_
-#define PRM_MODULE_DISCOVERY_LIB_H_
+#pragma once
 
 #include <Base.h>
 #include <PrmContextBuffer.h>
@@ -56,5 +55,3 @@ DiscoverPrmModules (
   OUT UINTN  *ModuleCount    OPTIONAL,
   OUT UINTN  *HandlerCount   OPTIONAL
   );
-
-#endif

PrmPkg/Include/Library/PrmPeCoffLib.h

@@ -8,8 +8,7 @@
 
 **/
 
-#ifndef PRM_PECOFF_LIB_H_
-#define PRM_PECOFF_LIB_H_
+#pragma once
 
 #include <Base.h>
 #include <PrmExportDescriptor.h>
@@ -107,5 +106,3 @@ GetExportEntryAddress (
   IN  EFI_IMAGE_EXPORT_DIRECTORY  *ImageExportDirectory,
   OUT EFI_PHYSICAL_ADDRESS        *ExportPhysicalAddress
   );
-
-#endif

PrmPkg/Include/Prm.h

@@ -8,8 +8,7 @@
 
 **/
 
-#ifndef PRM_H_
-#define PRM_H_
+#pragma once
 
 #include <Uefi.h>
 #include <PrmContextBuffer.h>
@@ -48,5 +47,3 @@ EFI_STATUS
   IN VOID                 *ParameterBuffer  OPTIONAL,
   IN PRM_CONTEXT_BUFFER   *ContextBuffer  OPTIONAL
   );
-
-#endif

PrmPkg/Include/PrmContextBuffer.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_CONTEXT_BUFFER_H_
-#define PRM_CONTEXT_BUFFER_H_
+#pragma once
 
 #include <PrmDataBuffer.h>
 #include <PrmMmio.h>
@@ -167,5 +166,3 @@ typedef struct {
 } PRM_MODULE_CONTEXT_BUFFERS;
 
 #pragma pack(pop)
-
-#endif

PrmPkg/Include/PrmDataBuffer.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_DATA_BUFFER_H_
-#define PRM_DATA_BUFFER_H_
+#pragma once
 
 #include <Uefi.h>
 
@@ -47,5 +46,3 @@ typedef struct {
 } PRM_DATA_BUFFER;
 
 #pragma pack(pop)
-
-#endif

PrmPkg/Include/PrmExportDescriptor.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_EXPORT_DESCRIPTOR_H_
-#define PRM_EXPORT_DESCRIPTOR_H_
+#pragma once
 
 #include <Prm.h>
 
@@ -106,4 +105,3 @@ typedef struct {
     { __VA_ARGS__ }                                                                                       \
   }                                                                                                       \
 
-#endif

PrmPkg/Include/PrmMmio.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_MMIO_H_
-#define PRM_MMIO_H_
+#pragma once
 
 #include <Uefi.h>
 
@@ -41,5 +40,3 @@ typedef struct {
 } PRM_RUNTIME_MMIO_RANGES;
 
 #pragma pack(pop)
-
-#endif

PrmPkg/Include/PrmModule.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_MODULE_H_
-#define PRM_MODULE_H_
+#pragma once
 
 #include <Prm.h>
 #include <PrmContextBuffer.h>
@@ -44,4 +43,3 @@
     IN PRM_CONTEXT_BUFFER   *ContextBuffer      \
     )                                           \
 
-#endif

PrmPkg/Include/PrmModuleImageContext.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_MODULE_IMAGE_CONTEXT_H_
-#define PRM_MODULE_IMAGE_CONTEXT_H_
+#pragma once
 
 #include <IndustryStandard/PeImage.h>
 #include <Library/PeCoffLib.h>
@@ -24,5 +23,3 @@ typedef struct {
 } PRM_MODULE_IMAGE_CONTEXT;
 
 #pragma pack(pop)
-
-#endif

PrmPkg/Include/Protocol/PrmConfig.h

@@ -11,8 +11,7 @@
 
 **/
 
-#ifndef PRM_CONFIG_H_
-#define PRM_CONFIG_H_
+#pragma once
 
 #include <PrmContextBuffer.h>
 #include <Uefi.h>
@@ -27,5 +26,3 @@ struct _PRM_CONFIG_PROTOCOL {
 };
 
 extern EFI_GUID  gPrmConfigProtocolGuid;
-
-#endif

PrmPkg/Library/DxePrmModuleDiscoveryLib/PrmModuleDiscovery.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef PRM_MODULE_DISCOVERY_H_
-#define PRM_MODULE_DISCOVERY_H_
+#pragma once
 
 #include <PrmModuleImageContext.h>
 
@@ -35,5 +34,3 @@ PRM_MODULE_IMAGE_CONTEXT_LIST_ENTRY *
 CreateNewPrmModuleImageContextListEntry (
   VOID
   );
-
-#endif

PrmPkg/PrmLoaderDxe/PrmAcpiTable.h

@@ -8,8 +8,7 @@
 
 **/
 
-#ifndef PRMT_ACPI_TABLE_H_
-#define PRMT_ACPI_TABLE_H_
+#pragma once
 
 #include <Base.h>
 #include <IndustryStandard/Acpi10.h>
@@ -92,5 +91,3 @@ typedef struct {
       PhysicalAddress,                                                     /* UINT64                  PhysicalAddress         */   \
     } \
   }
-
-#endif // _PRMT_ACPI_TABLE_H_

PrmPkg/Samples/PrmSampleContextBufferModule/Include/StaticData.h

@@ -8,8 +8,7 @@
 
 **/
 
-#ifndef PRM_STATIC_DATA_SAMPLE_CONTEXT_BUFFER_MODULE_H_
-#define PRM_STATIC_DATA_SAMPLE_CONTEXT_BUFFER_MODULE_H_
+#pragma once
 
 #include <Base.h>
 
@@ -20,5 +19,3 @@ typedef struct {
   BOOLEAN    Policy2Enabled;
   UINT8      SomeValueArray[SOME_VALUE_ARRAY_MAX_VALUES];
 } STATIC_DATA_SAMPLE_CONTEXT_BUFFER_MODULE;
-
-#endif

PrmPkg/Samples/PrmSampleHardwareAccessModule/Hpet.h

@@ -12,8 +12,7 @@
 
 **/
 
-#ifndef HPET_REGISTER_H_
-#define HPET_REGISTER_H_
+#pragma once
 
 #define HPET_BASE_ADDRESS  0xFED00000
 #define HPET_RANGE_LENGTH  0x1000
@@ -104,5 +103,3 @@ typedef union {
 } HPET_TIMER_MSI_ROUTE_REGISTER;
 
 #pragma pack()
-
-#endif