Added release notes for clangd 8

[ilya-biryukov]

LGTM

clang-tools-extra/docs/ReleaseNotes.rst

76

NIT: s/code actions/fixes

"code actions" sounds a bit too general here

[gribozavr]

.

clang-tools-extra/docs/ReleaseNotes.rst

 Some of the major new features and improvements to Extra Clang Tools are listed
 here. Generic improvements to Extra Clang Tools as a whole or to its underlying
 infrastructure are described first, followed by tool-specific sections.
 
 
 Improvements to clangd
 ----------------------
 
-The improvements are...
+- clangd now adds namespace qualifiers in code completion, for example, if you
+  type "``vec``", the list of completions will include "``std::vector``".
+
+  See also: `r343248 <https://reviews.llvm.org/rL343248>`__.
+
+- When a :ref:`global index <project-wide-index>` is available, clangd will use it to augment the
+  results of "go to definition" and "find references" queries. Global index
+  also enables global code completion, which suggests symbols that are not
+  imported in the current file and automatically inserts the missing
+  ``#include`` directives.
+
+- clangd stores the symbol index on disk in a new compact binary serialization
+  format.  It is 10x more compact than YAML and 40% more compact than gzipped
+  YAML.
+
+  See also: `r341375 <https://reviews.llvm.org/rL341375>`__.
+
+- clangd has a new efficient symbol index suitable for complex and fuzzy
+  queries and large code bases (e.g., LLVM, Chromium).  This index is used for
+  code completion, go to definition, and cross-references.  The architecture of
+  the index allows for complex and fuzzy retrieval criteria and sophisticated
+  scoring.
+
+  See also: `discussion on the mailing list
+  <http://lists.llvm.org/pipermail/cfe-dev/2018-July/058487.html>`__, `design
+  doc
+  <https://docs.google.com/document/d/1C-A6PGT6TynyaX4PXyExNMiGmJ2jL1UwV91Kyx11gOI/edit>`__.
+
+- clangd has a new LSP extension that communicates information about activity
+  on clangd's per-file worker thread.  This information can be displayed to
+  users to let them know that the language server is busy with something.  For
+  example, in clangd, building the AST blocks many other operations.
+
+  More info: :ref:`lsp-extension-file-status`.
+
+- clangd has a new LSP extension that allows the client to supply the
+  compilation commands over LSP, instead of finding compile_commands.json on
+  disk.
+
+  More info: :ref:`lsp-extension-compilation-commands`.
+
+- clangd has a new LSP extension that allows the client to request code actions
+  to be sent together with diagnostics, instead of asynchronously.
+
+  More info: :ref:`lsp-extension-code-actions-in-diagnostics`.
+
+- clangd has a new LSP extension that allows the client to resolve a symbol in
+  a light-weight manner, without retrieving further information (like
+  definition location, which may require consulting an index).
+
+  More info: :ref:`lsp-extension-symbol-info`.
 
 
 Improvements to clang-query
 ---------------------------
 
 - A new command line parameter ``--preload`` was added to
   run commands from a file and then start the interactive interpreter.
 

clang-tools-extra/docs/clangd/Extensions.rst

 
 Parameter: ``TextDocumentIdentifier``: an open file.
 
 Result: ``string``: the URI of the corresponding header (if a source file was
 provided) or source file (if a header was provided).
 
 If the corresponding file can't be determined, ``""`` is returned.
 
+.. _lsp-extension-file-status:
+
 File status
 ===========
 
 *This extension is supported in clangd 8 and newer.*
 
 It is important to provide feedback to the user when the UI is not responsive.
 
 This extension provides information about activity on clangd's per-file worker

 
 - ``uri : string``: the document whose status is being updated.
 - ``state : string``: human-readable information about current activity.
 
 **New initialization option**: ``initializationOptions.clangdFileStatus : bool``
 
 Enables receiving ``textDocument/clangd.fileStatus`` notifications.
 
+.. _lsp-extension-compilation-commands:
+
 Compilation commands
 ====================
 
 *This extension is supported in clangd 8 and newer.*
 
 clangd relies on knowing accurate compilation options to correctly interpret a
 file. Typically they are found in a ``compile_commands.json`` file in a
 directory that contains the file, or an ancestor directory. The following

 
 A human-readable name for a group of related diagnostics.  Diagnostics with the
 same code will always have the same category.
 
 **New client capability**: ``textDocument.publishDiagnostics.categorySupport``:
 
 Requests that clangd send ``Diagnostic.category``.
 
+.. _lsp-extension-code-actions-in-diagnostics:
+
 Inline fixes for diagnostics
 ============================
 
 *This extension is supported in clangd 8 and newer.*
 
 LSP specifies that code actions for diagnostics (fixes) are retrieved
 asynchronously using ``textDocument/codeAction``. clangd always computes fixes
 eagerly.  Providing them alongside diagnostics can improve the UX in editors.
 
 **New property of** ``Diagnostic`` **object**: ``codeActions : CodeAction[]``:
 
 All the code actions that address this diagnostic.
 
 **New client capability**: ``textDocument.publishDiagnostics.codeActionsInline : bool``
 
 Requests clangd to send ``Diagnostic.codeActions``.
 
+.. _lsp-extension-symbol-info:
+
 Symbol info request
 ===================
 
 *This extension is supported in clangd 8 and newer.*
 
 **New client->server request**: ``textDocument/symbolInfo``:
 
 This request attempts to resolve the symbol under the cursor, without

clang-tools-extra/docs/clangd/Installation.rst

 If all files in a project use the same build flags, you can put those flags,
 one flag per line, in ``compile_flags.txt`` in your source root.
 
 Clangd will assume the compile command is ``clang $FLAGS some_file.cc``.
 
 Creating this file by hand is a reasonable place to start if your project is
 quite simple.
 
+.. _project-wide-index:
+
 Project-wide Index
 ==================
 
 By default clangd only has a view on symbols coming from files you are
 currently editing. You can extend this view to whole project by providing a
 project-wide index to clangd.  There are two ways to do this.
 
 - Pass an experimental `-background-index` command line argument.  With