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using it to detect whether or not a terminal supports colors. This replaces a particularly egregious hack that merely compared the TERM environment variable to "dumb". That doesn't really translate to a reasonable experience for users that have actually ensured their terminal's capabilities are accurately reflected. This makes testing a terminal for color support somewhat more expensive, but it is called very rarely anyways. The important fast path when the output is being piped somewhere is already in place. The global lock may seem excessive, but the spec for calling into curses is *terrible*. The whole library is terrible, and I spent quite a bit of time looking for a better way of doing this before convincing myself that this was the fundamentally correct way to behave. The damage of the curses library is very narrowly confined, and we continue to use raw escape codes for actually manipulating the colors which is a much sane system than directly using curses here (IMO). If this causes trouble for folks, please let me know. I've tested it on Linux and will watch the bots carefully. I've also worked to account for the variances of curses interfaces that I could finde documentation for, but that may not have been sufficient. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187874 91177308-0d34-0410-b5e6-96231b3b80d8
Design Of lib/System
====================
The software in this directory is designed to completely shield LLVM from any
and all operating system specific functionality. It is not intended to be a
complete operating system wrapper (such as ACE), but only to provide the
functionality necessary to support LLVM.
The software located here, of necessity, has very specific and stringent design
rules. Violation of these rules means that cracks in the shield could form and
the primary goal of the library is defeated. By consistently using this library,
LLVM becomes more easily ported to new platforms since the only thing requiring
porting is this library.
Complete documentation for the library can be found in the file:
llvm/docs/SystemLibrary.html
or at this URL:
http://llvm.org/docs/SystemLibrary.html
While we recommend that you read the more detailed documentation, for the
impatient, here's a high level summary of the library's requirements.
1. No system header files are to be exposed through the interface.
2. Std C++ and Std C header files are okay to be exposed through the interface.
3. No exposed system-specific functions.
4. No exposed system-specific data.
5. Data in lib/System classes must use only simple C++ intrinsic types.
6. Errors are handled by returning "true" and setting an optional std::string
7. Library must not throw any exceptions, period.
8. Interface functions must not have throw() specifications.
9. No duplicate function impementations are permitted within an operating
system class.
To accomplish these requirements, the library has numerous design criteria that
must be satisfied. Here's a high level summary of the library's design criteria:
1. No unused functionality (only what LLVM needs)
2. High-Level Interfaces
3. Use Opaque Classes
4. Common Implementations
5. Multiple Implementations
6. Minimize Memory Allocation
7. No Virtual Methods