ShellPkg: 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>

ShellPkg/Application/Shell/ConsoleLogger.h

@@ -5,8 +5,7 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
-#ifndef _CONSOLE_LOGGER_HEADER_
-#define _CONSOLE_LOGGER_HEADER_
+#pragma once
 
 #include "Shell.h"
 
@@ -312,5 +311,3 @@ EFI_STATUS
 ConsoleLoggerResetBuffers (
   IN CONSOLE_LOGGER_PRIVATE_DATA  *ConsoleInfo
   );
-
-#endif //_CONSOLE_LOGGER_HEADER_

ShellPkg/Application/Shell/ConsoleWrappers.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef _SHELL_CONSOLE_WRAPPERS_HEADER_
-#define _SHELL_CONSOLE_WRAPPERS_HEADER_
+#pragma once
 
 /**
   Function to create a EFI_SIMPLE_TEXT_INPUT_PROTOCOL on top of a
@@ -69,5 +68,3 @@ EFI_STATUS
 CloseSimpleTextOutOnFile (
   IN EFI_SIMPLE_TEXT_OUTPUT_PROTOCOL  *SimpleTextOut
   );
-
-#endif //_SHELL_CONSOLE_WRAPPERS_HEADER_

ShellPkg/Application/Shell/FileHandleInternal.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _FILE_HANDLE_INTERNAL_HEADER_
-#define _FILE_HANDLE_INTERNAL_HEADER_
+#pragma once
 
 /**
   Move the cursor position one character backward.
@@ -54,5 +53,3 @@ PrintCommandHistory (
   IN CONST UINTN  TotalRows,
   IN CONST UINTN  StartColumn
   );
-
-#endif //_FILE_HANDLE_INTERNAL_HEADER_

ShellPkg/Application/Shell/FileHandleWrappers.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELL_FILE_HANDLE_WRAPPERS_HEADER_
-#define _SHELL_FILE_HANDLE_WRAPPERS_HEADER_
+#pragma once
 
 typedef struct {
   LIST_ENTRY    Link;
@@ -82,5 +81,3 @@ CreateFileInterfaceFile (
   IN CONST EFI_FILE_PROTOCOL  *Template,
   IN CONST BOOLEAN            Unicode
   );
-
-#endif //_SHELL_FILE_HANDLE_WRAPPERS_HEADER_

ShellPkg/Application/Shell/Shell.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef _SHELL_INTERNAL_HEADER_
-#define _SHELL_INTERNAL_HEADER_
+#pragma once
 
 #include <Uefi.h>
 
@@ -382,5 +381,3 @@ VOID
 RestoreBufferList (
   IN OUT LIST_ENTRY  *OldBufferList
   );
-
-#endif //_SHELL_INTERNAL_HEADER_

ShellPkg/Application/Shell/ShellEnvVar.h

@@ -11,8 +11,7 @@
 
 **/
 
-#ifndef _SHELL_ENVIRONMENT_VARIABLE_HEADER_
-#define _SHELL_ENVIRONMENT_VARIABLE_HEADER_
+#pragma once
 
 typedef struct {
   LIST_ENTRY    Link;
@@ -276,5 +275,3 @@ VOID
 ShellFreeEnvVarList (
   VOID
   );
-
-#endif //_SHELL_ENVIRONMENT_VARIABLE_HEADER_

ShellPkg/Application/Shell/ShellManParser.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELL_MAN_FILE_PARSER_HEADER_
-#define _SHELL_MAN_FILE_PARSER_HEADER_
+#pragma once
 
 /**
   This function returns the help information for the specified command. The help text
@@ -73,5 +72,3 @@ ManFileFindSections (
   OUT UINTN             *HelpSize,
   IN BOOLEAN            Ascii
   );
-
-#endif //_SHELL_MAN_FILE_PARSER_HEADER_

ShellPkg/Application/Shell/ShellParametersProtocol.h

@@ -7,8 +7,7 @@
 
 **/
 
-#ifndef _SHELL_PARAMETERS_PROTOCOL_PROVIDER_HEADER_
-#define _SHELL_PARAMETERS_PROTOCOL_PROVIDER_HEADER_
+#pragma once
 
 #include "Shell.h"
 
@@ -206,5 +205,3 @@ GetNextParameter (
   IN CONST UINTN  Length,
   IN BOOLEAN      StripQuotation
   );
-
-#endif //_SHELL_PARAMETERS_PROTOCOL_PROVIDER_HEADER_

ShellPkg/Application/Shell/ShellProtocol.h

@@ -8,8 +8,7 @@
 
 **/
 
-#ifndef _SHELL_PROTOCOL_HEADER_
-#define _SHELL_PROTOCOL_HEADER_
+#pragma once
 
 #include "Shell.h"
 
@@ -934,5 +933,3 @@ EFIAPI
 NotificationFunction (
   IN EFI_KEY_DATA  *KeyData
   );
-
-#endif //_SHELL_PROTOCOL_HEADER_

ShellPkg/DynamicCommand/DpDynamicCommand/Dp.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _DP_H_
-#define _DP_H_
+#pragma once
 
 #include <Uefi.h>
 
@@ -136,5 +135,3 @@ EFI_HII_HANDLE
 InitializeHiiPackage (
   EFI_HANDLE  ImageHandle
   );
-
-#endif // _DP_H_

ShellPkg/DynamicCommand/DpDynamicCommand/DpInternal.h

@@ -11,8 +11,7 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
-#ifndef _DP_INTELNAL_H_
-#define _DP_INTELNAL_H_
+#pragma once
 
 #define DP_GAUGE_STRING_LENGTH  36
 
@@ -311,5 +310,3 @@ VOID
 ProcessCumulative (
   IN PERF_CUM_DATA  *CustomCumulativeData OPTIONAL
   );
-
-#endif

ShellPkg/DynamicCommand/DpDynamicCommand/Literals.h

@@ -5,8 +5,7 @@
   SPDX-License-Identifier: BSD-2-Clause-Patent
 **/
 
-#ifndef _LITERALS_H_
-#define _LITERALS_H_
+#pragma once
 
 // ASCII String literals which probably don't need translation
 extern CHAR8 const  ALit_TimerLibError[];
@@ -23,5 +22,3 @@ extern CHAR8 const  ALit_DB_SUPPORT[];
 extern CHAR8 const  ALit_DB_STOP[];
 extern CHAR8 const  ALit_BdsTO[];
 extern CHAR8 const  ALit_PEIM[];
-
-#endif // _LITERALS_H_

ShellPkg/DynamicCommand/HttpDynamicCommand/Http.h

@@ -9,8 +9,7 @@
 
 **/
 
-#ifndef _HTTP_H_
-#define _HTTP_H_
+#pragma once
 
 #include <Uefi.h>
 
@@ -89,5 +88,3 @@ EFI_HII_HANDLE
 InitializeHiiPackage (
   IN EFI_HANDLE  ImageHandle
   );
-
-#endif // _HTTP_H_

ShellPkg/DynamicCommand/TftpDynamicCommand/Tftp.h

@@ -8,8 +8,7 @@
 
 **/
 
-#ifndef _TFTP_H_
-#define _TFTP_H_
+#pragma once
 
 #include <Uefi.h>
 
@@ -66,5 +65,3 @@ EFI_HII_HANDLE
 InitializeHiiPackage (
   EFI_HANDLE  ImageHandle
   );
-
-#endif // _TFTP_H_

ShellPkg/DynamicCommand/VariablePolicyDynamicCommand/VariablePolicy.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef VAR_POLICY_DYNAMIC_SHELL_COMMAND_H_
-#define VAR_POLICY_DYNAMIC_SHELL_COMMAND_H_
+#pragma once
 
 #include <Uefi.h>
 #include <Protocol/Shell.h>
@@ -125,5 +124,3 @@ RunVarPolicy (
   IN EFI_HANDLE        ImageHandle,
   IN EFI_SYSTEM_TABLE  *SystemTable
   );
-
-#endif

ShellPkg/Include/Guid/ShellAliasGuid.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELL_ALIAS_VARIABLE_GUID_H_
-#define _SHELL_ALIAS_VARIABLE_GUID_H_
+#pragma once
 
 #define SHELL_ALIAS_VARIABLE_GUID \
 { \
@@ -15,5 +14,3 @@
 }
 
 extern EFI_GUID  gShellAliasGuid;
-
-#endif

ShellPkg/Include/Guid/ShellEnvironment2Ext.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELLPKG_SHELL_ENV2_EXT_GUID_H_
-#define _SHELLPKG_SHELL_ENV2_EXT_GUID_H_
+#pragma once
 
 #define SHELLPKG_SHELL_ENV2_EXT_GUID \
 { \
@@ -15,5 +14,3 @@
 }
 
 extern EFI_GUID  gEfiShellEnvironment2ExtGuid;
-
-#endif

ShellPkg/Include/Guid/ShellLibHiiGuid.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELLLIB_HII_GUID_H_
-#define _SHELLLIB_HII_GUID_H_
+#pragma once
 
 #define HANDLE_PARSING_HII_GUID \
   { \
@@ -81,5 +80,3 @@ extern EFI_GUID  gShellNetwork2HiiGuid;
 extern EFI_GUID  gShellTftpHiiGuid;
 extern EFI_GUID  gShellHttpHiiGuid;
 extern EFI_GUID  gShellBcfgHiiGuid;
-
-#endif

ShellPkg/Include/Guid/ShellMapGuid.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELL_MAP_GUID_H_
-#define _SHELL_MAP_GUID_H_
+#pragma once
 
 #define SHELL_MAP_GUID \
 { \
@@ -15,5 +14,3 @@
 }
 
 extern EFI_GUID  gShellMapGuid;
-
-#endif

ShellPkg/Include/Guid/ShellPkgTokenSpace.h

@@ -6,8 +6,7 @@
 
 **/
 
-#ifndef _SHELLPKG_TOKEN_SPACE_GUID_H_
-#define _SHELLPKG_TOKEN_SPACE_GUID_H_
+#pragma once
 
 #define EFI_SHELLPKG_TOKEN_SPACE_GUID \
 { \
@@ -15,5 +14,3 @@
 }
 
 extern EFI_GUID  gEfiShellPkgTokenSpaceGuid;
-
-#endif