MAINT-4744: Eliminate viewer dependency on (old) GNU libstdc++.

To be more accurate, this changeset doesn't actually eliminate the dependency:
it eliminates the use cases for the llifstream / llofstream feature that
requires it.
Currently you can construct an llifstream or llofstream from an open LLFILE*
file handle (or, except on Windows, an int file descriptor). But rather than
containing a streambuf implementation based on FILE*, llfile.h relies on the
fact that the Windows std::filebuf happens to support that as a nonstandard
extension; also on a nonstandard GNU extension __gnu_cxx::stdio_filebuf<char>.
To move from GNU libstdc++ to clang's libc++ (the direction on Mac), we could
code a streambuf that supports FILE*. But before doing that, it's worth asking
whether anyone actually uses this questionable feature.
In fact there were only two methods: LLWearable::exportFile() and importFile()
-- and only one call to either, in LLViewerWearable::saveNewAsset(). The code
in saveNewAsset() opened the LLFILE* immediately before calling exportFile(),
meaning we could reasonably push the open operation down into exportFile().
That logic was complex anyway due to the need for the caller to close the
LLFILE* regardless of the success of the exportFile().
Change LLWearable::exportFile() and importFile() to accept a std::string
filename rather than an open LLFILE*. Change LLViewerWearable::saveNewAsset()
to simply call exportFile(filename) rather than horsing around with an LLFILE*
handle. (This improves the code in another way too: it encapsulates the need
to open the relevant file in binary mode. Previously, each caller had to
remember to do that.)
To prevent inadvertent reintroduction of ll[io]fstream(LLFILE*) code, add
llstream_LLFILE preprocessor macro (default 0) to control access to the
relevant constructors. Also suppress rdbuf() override, the only method whose
signature references llstdio_filebuf.

2 files changed, 18 insertions, 0 deletions

diff --git a/indra/llcommon/llfile.cpp b/indra/llcommon/llfile.cpp
index aabc195ba8..304d702979 100755
--- a/indra/llcommon/llfile.cpp
+++ b/indra/llcommon/llfile.cpp
@@ -919,6 +919,7 @@ llifstream::llifstream(const char* _Filename,
 #endif
 
 
+#if llstream_LLFILE
 // explicit
 llifstream::llifstream(_Filet *_File,
 		ios_base::openmode _Mode, size_t _Size) :
@@ -942,6 +943,7 @@ llifstream::llifstream(int __fd,
 	this->init(&_M_filebuf);
 }
 #endif
+#endif // llstream_LLFILE
 
 bool llifstream::is_open() const
 {	// test if C stream has been opened
@@ -1039,6 +1041,7 @@ llofstream::llofstream(const char* _Filename,
 }
 #endif
 
+#if llstream_LLFILE
 // explicit
 llofstream::llofstream(_Filet *_File,
 			ios_base::openmode _Mode, size_t _Size) :
@@ -1062,6 +1065,7 @@ llofstream::llofstream(int __fd,
 	this->init(&_M_filebuf);
 }
 #endif
+#endif // llstream_LLFILE
 
 bool llofstream::is_open() const
 {	// test if C stream has been opened
diff --git a/indra/llcommon/llfile.h b/indra/llcommon/llfile.h
index 0612071d67..44a1e42fa5 100755
--- a/indra/llcommon/llfile.h
+++ b/indra/llcommon/llfile.h
@@ -86,6 +86,12 @@ public:
 	static  const char * tmpdir();
 };
 
+// Remove ll[io]fstream support for [LL]FILE*, preparing to remove dependency
+// on GNU's standard library.
+#if ! defined(llstream_LLFILE)
+#define llstream_LLFILE 0
+#endif
+
 /**
  *  @brief Provides a layer of compatibility for C/POSIX.
  *
@@ -228,6 +234,7 @@ public:
 	explicit llifstream(const char* _Filename,
 			ios_base::openmode _Mode = ios_base::in);
 
+#if llstream_LLFILE
 	/**
 	 *  @brief  Create a stream using an open c file stream.
 	 *  @param  File  An open @c FILE*.
@@ -253,6 +260,7 @@ public:
 			//size_t _Size = static_cast<size_t>(BUFSIZ));
 			size_t _Size = static_cast<size_t>(1));
 #endif
+#endif // llstream_LLFILE
 
 	/**
 	 *  @brief  The destructor does nothing.
@@ -263,6 +271,7 @@ public:
 	virtual ~llifstream() {}
 
 	// Members:
+#if llstream_LLFILE
 	/**
 	 *  @brief  Accessing the underlying buffer.
 	 *  @return  The current basic_filebuf buffer.
@@ -271,6 +280,7 @@ public:
 	*/
 	llstdio_filebuf* rdbuf() const
 	{ return const_cast<llstdio_filebuf*>(&_M_filebuf); }
+#endif // llstream_LLFILE
 
 	/**
 	 *  @brief  Wrapper to test for an open file.
@@ -340,6 +350,7 @@ public:
 	explicit llofstream(const char* _Filename,
 			ios_base::openmode _Mode = ios_base::out|ios_base::trunc);
 
+#if llstream_LLFILE
 	/**
 	 *  @brief  Create a stream using an open c file stream.
 	 *  @param  File  An open @c FILE*.
@@ -365,6 +376,7 @@ public:
 			//size_t _Size = static_cast<size_t>(BUFSIZ));
 			size_t _Size = static_cast<size_t>(1));
 #endif
+#endif // llstream_LLFILE
 
 	/**
 	 *  @brief  The destructor does nothing.
@@ -375,6 +387,7 @@ public:
 	virtual ~llofstream() {}
 
 	// Members:
+#if llstream_LLFILE
 	/**
 	 *  @brief  Accessing the underlying buffer.
 	 *  @return  The current basic_filebuf buffer.
@@ -383,6 +396,7 @@ public:
 	*/
 	llstdio_filebuf* rdbuf() const
 	{ return const_cast<llstdio_filebuf*>(&_M_filebuf); }
+#endif // llstream_LLFILE
 
 	/**
 	 *  @brief  Wrapper to test for an open file.