docs: Convert some docs to reST.

Converts:
    LanguageExtensions
    LibASTMatchers
    LibTooling
    PCHInternals
    ThreadSanitizer
    Tooling

Patch by Mykhailo Pustovit!
(with minor edits by Dmitri Gribenko and Sean Silva)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@170048 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 100 insertions, 0 deletions

diff --git a/docs/Tooling.rst b/docs/Tooling.rst
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+===================
+Writing Clang Tools
+===================
+
+Clang provides infrastructure to write tools that need syntactic and semantic
+information about a program.  This document will give a short introduction of
+the different ways to write clang tools, and their pros and cons.
+
+LibClang
+--------
+
+`LibClang <http://clang.llvm.org/doxygen/group__CINDEX.html>`_ is a stable high
+level C interface to clang.  When in doubt LibClang is probably the interface
+you want to use.  Consider the other interfaces only when you have a good
+reason not to use LibClang.
+
+Canonical examples of when to use LibClang:
+
+* Xcode
+* Clang Python Bindings
+
+Use LibClang when you...:
+
+* want to interface with clang from other languages than C++
+* need a stable interface that takes care to be backwards compatible
+* want powerful high-level abstractions, like iterating through an AST with a
+  cursor, and don't want to learn all the nitty gritty details of Clang's AST.
+
+Do not use LibClang when you...:
+
+* want full control over the Clang AST
+
+Clang Plugins
+-------------
+
+`Clang Plugins <ClangPlugins.html>`_ allow you to run additional actions on the
+AST as part of a compilation.  Plugins are dynamic libraries that are loaded at
+runtime by the compiler, and they're easy to integrate into your build
+environment.
+
+Canonical examples of when to use Clang Plugins:
+
+* special lint-style warnings or errors for your project
+* creating additional build artifacts from a single compile step
+
+Use Clang Plugins when you...:
+
+* need your tool to rerun if any of the dependencies change
+* want your tool to make or break a build
+* need full control over the Clang AST
+
+Do not use Clang Plugins when you...:
+
+* want to run tools outside of your build environment
+* want full control on how Clang is set up, including mapping of in-memory
+  virtual files
+* need to run over a specific subset of files in your project which is not
+  necessarily related to any changes which would trigger rebuilds
+
+LibTooling
+----------
+
+`LibTooling <LibTooling.html>`_ is a C++ interface aimed at writing standalone
+tools, as well as integrating into services that run clang tools.  Canonical
+examples of when to use LibTooling:
+
+* a simple syntax checker
+* refactoring tools
+
+Use LibTooling when you...:
+
+* want to run tools over a single file, or a specific subset of files,
+  independently of the build system
+* want full control over the Clang AST
+* want to share code with Clang Plgins
+
+Do not use LibTooling when you...:
+
+* want to run as part of the build triggered by dependency changes
+* want a stable interface so you don't need to change your code when the AST API
+  changes
+* want high level abstractions like cursors and code completion out of the box
+* do not want to write your tools in C++
+
+Clang Tools
+-----------
+
+`Clang tools <ClangTools.html>`_ are a collection of specific developer tools
+built on top of the LibTooling infrastructure as part of the Clang project.
+They are targeted at automating and improving core development activities of
+C/C++ developers.
+
+Examples of tools we are building or planning as part of the Clang project:
+
+* Syntax checking (:program:`clang-check`)
+* Automatic fixing of compile errors (:program:`clang-fixit`)
+* Automatic code formatting
+* Migration tools for new features in new language standards
+* Core refactoring tools
+