ripgrep: migrate to libripgrep

This commit does the work to delete the old `grep` crate and effectively
rewrite most of ripgrep core to use the new libripgrep crates. The new
`grep` crate is now a facade that collects the various crates that make
up libripgrep.

The most complex part of ripgrep core is now arguably the translation
between command line parameters and the library options, which is
ultimately where we want to be.

1 files changed, 84 insertions, 34 deletions

diff --git a/README.md b/README.md
index 2b7ada60..351de389 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ available for [every release](https://github.com/BurntSushi/ripgrep/releases).
 ripgrep is similar to other popular search tools like The Silver Searcher,
 ack and grep.
 
-[![Linux build status](https://travis-ci.org/BurntSushi/ripgrep.svg?branch=master)](https://travis-ci.org/BurntSushi/ripgrep)
+[![Linux build status](https://travis-ci.org/BurntSushi/ripgrep.svg)](https://travis-ci.org/BurntSushi/ripgrep)
 [![Windows build status](https://ci.appveyor.com/api/projects/status/github/BurntSushi/ripgrep?svg=true)](https://ci.appveyor.com/project/BurntSushi/ripgrep)
 [![Crates.io](https://img.shields.io/crates/v/ripgrep.svg)](https://crates.io/crates/ripgrep)
 
@@ -85,14 +85,16 @@ increases the times to `2.640s` for ripgrep and `10.277s` for GNU grep.
 
 ### Why should I use ripgrep?
 
-* It can replace many use cases served by both The Silver Searcher and GNU grep
-  because it is generally faster than both. (See [the FAQ](FAQ.md#posix4ever)
-  for more details on whether ripgrep can truly replace grep.)
-* Like The Silver Searcher, ripgrep defaults to recursive directory search
-  and won't search files ignored by your `.gitignore` files. It also ignores
-  hidden and binary files by default. ripgrep also implements full support
-  for `.gitignore`, whereas there are many bugs related to that functionality
-  in The Silver Searcher.
+* It can replace many use cases served by other search tools
+  because it contains most of their features and is generally faster. (See
+  [the FAQ](FAQ.md#posix4ever) for more details on whether ripgrep can truly
+  replace grep.)
+* Like other tools specialized to code search, ripgrep defaults to recursive
+  directory search and won't search files ignored by your `.gitignore` files.
+  It also ignores hidden and binary files by default. ripgrep also implements
+  full support for `.gitignore`, whereas there are many bugs related to that
+  functionality in other code search tools claiming to provide the same
+  functionality.
 * ripgrep can search specific types of files. For example, `rg -tpy foo`
   limits your search to Python files and `rg -Tjs foo` excludes Javascript
   files from your search. ripgrep can be taught about new file types with
@@ -117,22 +119,24 @@ bugs, and Unicode support.
 
 ### Why shouldn't I use ripgrep?
 
-I'd like to try to convince you why you *shouldn't* use ripgrep. This should
-give you a glimpse at some important downsides or missing features of
-ripgrep.
+Despite initially not wanting to add every feature under the sun to ripgrep,
+over time, ripgrep has grown support for most features found in other file
+searching tools. This includes searching for results spanning across multiple
+lines, and opt-in support for PCRE2, which provides look-around and
+backreference support.
 
-* ripgrep uses a regex engine based on finite automata, so if you want fancy
-  regex features such as backreferences or lookaround, ripgrep won't provide
-  them to you. ripgrep does support lots of things though, including, but not
-  limited to: lazy quantification (e.g., `a+?`), repetitions (e.g., `a{2,5}`),
-  begin/end assertions (e.g., `^\w+$`), word boundaries (e.g., `\bfoo\b`), and
-  support for Unicode categories (e.g., `\p{Sc}` to match currency symbols or
-  `\p{Lu}` to match any uppercase letter). (Fancier regexes will never be
-  supported.)
-* ripgrep doesn't have multiline search. (Will happen as an opt-in feature.)
+At this point, the primary reasons not to use ripgrep probably consist of one
+or more of the following:
 
-In other words, if you like fancy regexes or multiline search, then ripgrep
-may not quite meet your needs (yet).
+* You need a portable and ubiquitous tool. While ripgrep works on Windows,
+  macOS and Linux, it is not ubiquitous and it does not conform to any
+  standard such as POSIX. The best tool for this job is good old grep.
+* There still exists some other minor feature (or bug) found in another tool
+  that isn't in ripgrep.
+* There is a performance edge case where ripgrep doesn't do well where another
+  tool does do well. (Please file a bug report!)
+* ripgrep isn't possible to install on your machine or isn't available for your
+  platform. (Please file a bug report!)
 
 
 ### Is it really faster than everything else?
@@ -145,7 +149,8 @@ Summarizing, ripgrep is fast because:
 * It is built on top of
   [Rust's regex engine](https://github.com/rust-lang-nursery/regex).
   Rust's regex engine uses finite automata, SIMD and aggressive literal
-  optimizations to make searching very fast.
+  optimizations to make searching very fast. (PCRE2 support can be opted into
+  with the `-P/--pcre2` flag.)
 * Rust's regex library maintains performance with full Unicode support by
   building UTF-8 decoding directly into its deterministic finite automaton
   engine.
@@ -168,6 +173,11 @@ Andy Lester, author of [ack](https://beyondgrep.com/), has published an
 excellent table comparing the features of ack, ag, git-grep, GNU grep and
 ripgrep: https://beyondgrep.com/feature-comparison/
 
+Note that ripgrep has grown a few significant new features recently that
+are not yet present in Andy's table. This includes, but is not limited to,
+configuration files, passthru, support for searching compressed files,
+multiline search and opt-in fancy regex support via PCRE2.
+
 
 ### Installation
 
@@ -207,13 +217,15 @@ If you're a **MacPorts** user, then you can install ripgrep from the
 $ sudo port install ripgrep
 ```
 
-If you're a **Windows Chocolatey** user, then you can install ripgrep from the [official repo](https://chocolatey.org/packages/ripgrep):
+If you're a **Windows Chocolatey** user, then you can install ripgrep from the
+[official repo](https://chocolatey.org/packages/ripgrep):
 
 ```
 $ choco install ripgrep
 ```
 
-If you're a **Windows Scoop** user, then you can install ripgrep from the [official bucket](https://github.com/lukesampson/scoop/blob/master/bucket/ripgrep.json):
+If you're a **Windows Scoop** user, then you can install ripgrep from the
+[official bucket](https://github.com/lukesampson/scoop/blob/master/bucket/ripgrep.json):
 
 ```
 $ scoop install ripgrep
@@ -225,32 +237,37 @@ If you're an **Arch Linux** user, then you can install ripgrep from the official
 $ pacman -S ripgrep
 ```
 
-If you're a **Gentoo** user, you can install ripgrep from the [official repo](https://packages.gentoo.org/packages/sys-apps/ripgrep):
+If you're a **Gentoo** user, you can install ripgrep from the
+[official repo](https://packages.gentoo.org/packages/sys-apps/ripgrep):
 
 ```
 $ emerge sys-apps/ripgrep
 ```
 
-If you're a **Fedora 27+** user, you can install ripgrep from official repositories.
+If you're a **Fedora 27+** user, you can install ripgrep from official
+repositories.
 
 ```
 $ sudo dnf install ripgrep
 ```
 
-If you're a **Fedora 24+** user, you can install ripgrep from [copr](https://copr.fedorainfracloud.org/coprs/carlwgeorge/ripgrep/):
+If you're a **Fedora 24+** user, you can install ripgrep from
+[copr](https://copr.fedorainfracloud.org/coprs/carlwgeorge/ripgrep/):
 
 ```
 $ sudo dnf copr enable carlwgeorge/ripgrep
 $ sudo dnf install ripgrep
 ```
 
-If you're an **openSUSE Tumbleweed** user, you can install ripgrep from the [official repo](http://software.opensuse.org/package/ripgrep):
+If you're an **openSUSE Tumbleweed** user, you can install ripgrep from the
+[official repo](http://software.opensuse.org/package/ripgrep):
 
 ```
 $ sudo zypper install ripgrep
 ```
 
-If you're a **RHEL/CentOS 7** user, you can install ripgrep from [copr](https://copr.fedorainfracloud.org/coprs/carlwgeorge/ripgrep/):
+If you're a **RHEL/CentOS 7** user, you can install ripgrep from
+[copr](https://copr.fedorainfracloud.org/coprs/carlwgeorge/ripgrep/):
 
 ```
 $ sudo yum-config-manager --add-repo=https://copr.fedorainfracloud.org/coprs/carlwgeorge/ripgrep/repo/epel-7/carlwgeorge-ripgrep-epel-7.repo
@@ -286,25 +303,29 @@ seem to work right and generate a number of very strange bug reports that I
 don't know how to fix and don't have the time to fix. Therefore, it is no
 longer a recommended installation option.)
 
-If you're a **FreeBSD** user, then you can install ripgrep from the [official ports](https://www.freshports.org/textproc/ripgrep/):
+If you're a **FreeBSD** user, then you can install ripgrep from the
+[official ports](https://www.freshports.org/textproc/ripgrep/):
 
 ```
 # pkg install ripgrep
 ```
 
-If you're an **OpenBSD** user, then you can install ripgrep from the [official ports](http://openports.se/textproc/ripgrep):
+If you're an **OpenBSD** user, then you can install ripgrep from the
+[official ports](http://openports.se/textproc/ripgrep):
 
 ```
 $ doas pkg_add ripgrep
 ```
 
-If you're a **NetBSD** user, then you can install ripgrep from [pkgsrc](http://pkgsrc.se/textproc/ripgrep):
+If you're a **NetBSD** user, then you can install ripgrep from
+[pkgsrc](http://pkgsrc.se/textproc/ripgrep):
 
 ```
 # pkgin install ripgrep
 ```
 
 If you're a **Rust programmer**, ripgrep can be installed with `cargo`.
+
 * Note that the minimum supported version of Rust for ripgrep is **1.23.0**,
   although ripgrep may work with older versions.
 * Note that the binary may be bigger than expected because it contains debug
@@ -353,6 +374,35 @@ are not necessary to get SIMD optimizations for search; those are enabled
 automatically. Hopefully, some day, the `simd-accel` and `avx-accel` features
 will similarly become unnecessary.
 
+Finally, optional PCRE2 support can be built with ripgrep by enabling the
+`pcre2` feature:
+
+```
+$ cargo build --release --features 'pcre2'
+```
+
+(Tip: use `--features 'pcre2 simd-accel avx-accel'` to also include compile
+time SIMD optimizations.)
+
+Enabling the PCRE2 feature will attempt to automatically find and link with
+your system's PCRE2 library via `pkg-config`. If one doesn't exist, then
+ripgrep will build PCRE2 from source using your system's C compiler and then
+statically link it into the final executable. Static linking can be forced even
+when there is an available PCRE2 system library by either building ripgrep with
+the MUSL target or by setting `PCRE2_SYS_STATIC=1`.
+
+ripgrep can be built with the MUSL target on Linux by first installing the MUSL
+library on your system (consult your friendly neighborhood package manager).
+Then you just need to add MUSL support to your Rust toolchain and rebuild
+ripgrep, which yields a fully static executable:
+
+```
+$ rustup target add x86_64-unknown-linux-musl
+$ cargo build --release --target x86_64-unknown-linux-musl
+```
+
+Applying the `--features` flag from above works as expected.
+
 
 ### Running tests