mk: Depend on regex_macros for tests appropriately

There is currently not much precedent for target crates requiring syntax
extensions to compile their test versions. This dependency is possible, but
can't be encoded through the normal means of DEPS_regex because it is a
test-only dependency and it must be a *host* dependency (it's a syntax
extension).

Closes #13844
rustc: Enable -f{function,data}-sections

The compiler has previously been producing binaries on the order of 1.8MB for
hello world programs "fn main() {}". This is largely a result of the compilation
model used by compiling entire libraries into a single object file and because
static linking is favored by default.

When linking, linkers will pull in the entire contents of an object file if any
symbol from the object file is used. This means that if any symbol from a rust
library is used, the entire library is pulled in unconditionally, regardless of
whether the library is used or not.

Traditional C/C++ projects do not normally encounter these large executable
problems because their archives (rust's rlibs) are composed of many objects.
Because of this, linkers can eliminate entire objects from being in the final
executable. With rustc, however, the linker does not have the opportunity to
leave out entire object files.

In order to get similar benefits from dead code stripping at link time, this
commit enables the -ffunction-sections and -fdata-sections flags in LLVM, as
well as passing --gc-sections to the linker *by default*. This means that each
function and each global will be placed into its own section, allowing the
linker to GC all unused functions and data symbols.

By enabling these flags, rust is able to generate much smaller binaries default.
On linux, a hello world binary went from 1.8MB to 597K (a 67% reduction in
size). The output size of dynamic libraries remained constant, but the output
size of rlibs increased, as seen below:

    libarena         -  2.27% bigger (   292872 =>    299508)
    libcollections   -  0.64% bigger (  6765884 =>   6809076)
    libflate         -  0.83% bigger (   186516 =>    188060)
    libfourcc        - 14.71% bigger (   307290 =>    352498)
    libgetopts       -  4.42% bigger (   761468 =>    795102)
    libglob          -  2.73% bigger (   899932 =>    924542)
    libgreen         -  9.63% bigger (  1281718 =>   1405124)
    libhexfloat      - 13.88% bigger (   333738 =>    380060)
    liblibc          - 10.79% bigger (   551280 =>    610736)
    liblog           - 10.93% bigger (   218208 =>    242060)
    libnative        -  8.26% bigger (  1362096 =>   1474658)
    libnum           -  2.34% bigger (  2583400 =>   2643916)
    librand          -  1.72% bigger (  1608684 =>   1636394)
    libregex         -  6.50% bigger (  1747768 =>   1861398)
    librustc         -  4.21% bigger (151820192 => 158218924)
    librustdoc       -  8.96% bigger ( 13142604 =>  14320544)
    librustuv        -  4.13% bigger (  4366896 =>   4547304)
    libsemver        -  2.66% bigger (   396166 =>    406686)
    libserialize     -  1.91% bigger (  6878396 =>   7009822)
    libstd           -  3.59% bigger ( 39485286 =>  40902218)
    libsync          -  3.95% bigger (  1386390 =>   1441204)
    libsyntax        -  4.96% bigger ( 35757202 =>  37530798)
    libterm          - 13.99% bigger (   924580 =>   1053902)
    libtest          -  6.04% bigger (  2455720 =>   2604092)
    libtime          -  2.84% bigger (  1075708 =>   1106242)
    liburl           -  6.53% bigger (   590458 =>    629004)
    libuuid          -  4.63% bigger (   326350 =>    341466)
    libworkcache     -  8.45% bigger (  1230702 =>   1334750)

This increase in size is a result of encoding many more section names into each
object file (rlib). These increases are moderate enough that this change seems
worthwhile to me, due to the drastic improvements seen in the final artifacts.
The overall increase of the stage2 target folder (not the size of an install)
went from 337MB to 348MB (3% increase).

Additionally, linking is generally slower when executed with all these new
sections plus the --gc-sections flag. The stage0 compiler takes 1.4s to link the
`rustc` binary, where the stage1 compiler takes 1.9s to link the binary. Three
megabytes are shaved off the binary. I found this increase in link time to be
acceptable relative to the benefits of code size gained.

This commit only enables --gc-sections for *executables*, not dynamic libraries.
LLVM does all the heavy lifting when producing an object file for a dynamic
library, so there is little else for the linker to do (remember that we only
have one object file).

I conducted similar experiments by putting a *module's* functions and data
symbols into its own section (granularity moved to a module level instead of a
function/static level). The size benefits of a hello world were seen to be on
the order of 400K rather than 1.2MB. It seemed that enough benefit was gained
using ffunction-sections that this route was less desirable, despite the lesser
increases in binary rlib size.
auto merge of #13845 : alexcrichton/rust/regex-deps, r=brson

There is currently not much precedent for target crates requiring syntax
extensions to compile their test versions. This dependency is possible, but
can't be encoded through the normal means of DEPS_regex because it is a
test-only dependency and it must be a *host* dependency (it's a syntax
extension).

Closes #13844
auto merge of #13772 : brson/rust/cratedocs, r=alexcrichton

Also move prelude explanation to the prelude module.

This tries to provide a guide to what's in the standard library, organized bottom up from primitives to I/O.
auto merge of #13833 : alexcrichton/rust/ffunction-sections, r=thestinger

The compiler has previously been producing binaries on the order of 1.8MB for
hello world programs "fn main() {}". This is largely a result of the compilation
model used by compiling entire libraries into a single object file and because
static linking is favored by default.

When linking, linkers will pull in the entire contents of an object file if any
symbol from the object file is used. This means that if any symbol from a rust
library is used, the entire library is pulled in unconditionally, regardless of
whether the library is used or not.

Traditional C/C++ projects do not normally encounter these large executable
problems because their archives (rust's rlibs) are composed of many objects.
Because of this, linkers can eliminate entire objects from being in the final
executable. With rustc, however, the linker does not have the opportunity to
leave out entire object files.

In order to get similar benefits from dead code stripping at link time, this
commit enables the -ffunction-sections and -fdata-sections flags in LLVM, as
well as passing --gc-sections to the linker *by default*. This means that each
function and each global will be placed into its own section, allowing the
linker to GC all unused functions and data symbols.

By enabling these flags, rust is able to generate much smaller binaries default.
On linux, a hello world binary went from 1.8MB to 597K (a 67% reduction in
size). The output size of dynamic libraries remained constant, but the output
size of rlibs increased, as seen below:

    libarena       -  2.27% bigger
    libcollections -  0.64% bigger
    libflate       -  0.85% bigger
    libfourcc      - 14.67% bigger
    libgetopts     -  4.52% bigger
    libglob        -  2.74% bigger
    libgreen       -  9.68% bigger
    libhexfloat    - 13.68% bigger
    liblibc        - 10.79% bigger
    liblog         - 10.95% bigger
    libnative      -  8.34% bigger
    libnum         -  2.31% bigger
    librand        -  1.71% bigger
    libregex       -  6.43% bigger
    librustc       -  4.21% bigger
    librustdoc     -  8.98% bigger
    librustuv      -  4.11% bigger
    libsemver      -  2.68% bigger
    libserialize   -  1.92% bigger
    libstd         -  3.59% bigger
    libsync        -  3.96% bigger
    libsyntax      -  4.96% bigger
    libterm        - 13.96% bigger
    libtest        -  6.03% bigger
    libtime        -  2.86% bigger
    liburl         -  6.59% bigger
    libuuid        -  4.70% bigger
    libworkcache   -  8.44% bigger

This increase in size is a result of encoding many more section names into each
object file (rlib). These increases are moderate enough that this change seems
worthwhile to me, due to the drastic improvements seen in the final artifacts.
The overall increase of the stage2 target folder (not the size of an install)
went from 337MB to 348MB (3% increase).

Additionally, linking is generally slower when executed with all these new
sections plus the --gc-sections flag. The stage0 compiler takes 1.4s to link the
`rustc` binary, where the stage1 compiler takes 1.9s to link the binary. Three
megabytes are shaved off the binary. I found this increase in link time to be
acceptable relative to the benefits of code size gained.

This commit only enables --gc-sections for *executables*, not dynamic libraries.
LLVM does all the heavy lifting when producing an object file for a dynamic
library, so there is little else for the linker to do (remember that we only
have one object file).

I conducted similar experiments by putting a *module's* functions and data
symbols into its own section (granularity moved to a module level instead of a
function/static level). The size benefits of a hello world were seen to be on
the order of 400K rather than 1.2MB. It seemed that enough benefit was gained
using ffunction-sections that this route was less desirable, despite the lesser
increases in binary rlib size.
regex: General style tweaks.

For loops are nicer than manual whiles, etc.
auto merge of #13776 : adrientetar/rust/rustdoc-fix, r=brson

- Closes #13591. Relevant example: http://adrientetar.legtux.org/cached/rust-docs/struct.CChars.htm
(Had to use `!important` to override CSS selector precedence, namely matching over parent class.)
- Implement changes from #13780 feedback, namely:
  * Changed font-size from 18px to 15px
  * Reintroduced gray background for code samples
  * Tightened up the margins
- Fix point 1 and point 4 of #13804.

Samples:

- [enum.FileType](http://adrientetar.legtux.org/cached/rust-docs/enum.FileType.htm)
- [struct.CChars](http://adrientetar.legtux.org/cached/rust-docs/struct.CChars.htm)
- [std](http://adrientetar.legtux.org/cached/rust-docs/std.htm)
- [std::io](http://adrientetar.legtux.org/cached/rust-docs/io.htm).

r? @brson
Add a bitflags! macro

The `bitflags!` macro generates a `struct` that holds a set of C-style bitmask flags. It is useful for creating typesafe wrappers for C APIs.

For example:

~~~rust
#[feature(phase)];
#[phase(syntax)] extern crate collections;

bitflags!(Flags: u32 {
    FlagA       = 0x00000001,
    FlagB       = 0x00000010,
    FlagC       = 0x00000100,
    FlagABC     = FlagA.bits
                | FlagB.bits
                | FlagC.bits
})

fn main() {
    let e1 = FlagA | FlagC;
    let e2 = FlagB | FlagC;
    assert!((e1 | e2) == FlagABC);   // union
    assert!((e1 & e2) == FlagC);     // intersection
    assert!((e1 - e2) == FlagA);     // set difference
}
~~~
Document how generated bitflags can be extended with type and trait implementations
Document derived traits for bitset! macro
rustc: Add search paths to dylib load paths

When a syntax extension is loaded by the compiler, the dylib that is opened may
have other dylibs that it depends on. The dynamic linker must be able to find
these libraries on the system or else the library will fail to load.

Currently, unix gets by with the use of rpaths. This relies on the dylib not
moving around too drastically relative to its dependencies. For windows,
however, this is no rpath available, and in theory unix should work without
rpaths as well.

This modifies the compiler to add all -L search directories to the dynamic
linker's set of load paths. This is currently managed through environment
variables for each platform.

Closes #13848
auto merge of #13857 : alexcrichton/rust/add-dylib-paths, r=brson

When a syntax extension is loaded by the compiler, the dylib that is opened may
have other dylibs that it depends on. The dynamic linker must be able to find
these libraries on the system or else the library will fail to load.

Currently, unix gets by with the use of rpaths. This relies on the dylib not
moving around too drastically relative to its dependencies. For windows,
however, this is no rpath available, and in theory unix should work without
rpaths as well.

This modifies the compiler to add all -L search directories to the dynamic
linker's set of load paths. This is currently managed through environment
variables for each platform.

Closes #13848
auto merge of #12740 : nical/rust/json-streaming, r=erickt

Hi rust enthusiasts,

With this patch I propose to add a "streaming" API to the existing json parser in libserialize.

By "streaming" I mean a parser that let you act on JsonEvents that are generated as while parsing happens, as opposed to parsing the entire source, generating a big data structure and working with this data structure. I think both approaches have their pros and cons so this pull request adds the streaming API, preserving the existing one.

The streaming API is simple: It consist into an Iterator<JsonEvent> that consumes an Iterator<char>. JsonEvent is an enum with values such as NumberValue(f64), BeginList, EndList, BeginObject, etc.

The user would ideally use the API as follows:

```
for evt in StreamingParser::new(src) {
  match evt {
    BeginList => {
       // ...
    }
    // ...
  }
}
```

The iterator provides a stack() method returning a slice of StackNodes which represent "where we currently are" in the logical structure of the json stream (for instance at "foo.bar[3].x" you get [ Key("foo"), Key("bar"), Index(3), Key("x") ].)

I wrote "ideally" above because the current way rust expands for loops, you can't call the stack() method because the iterator is already borrowed. So for know you need to manually advance the iterator in the loop. I hope this is something we can cope with, until for loops are better integrated with the compiler.

Streaming parsers are useful when you want to read from a json stream, generate a custom data structure and you know how the json is going to be structured. For example, imagine you have to parse a 3D mesh file represented in the json format. In this case you probably expect to have large arrays of vertices and using the generic parser will be very inefficient because it will create a big list of all these vertices, which you will copy into a contiguous array afterwards (so you end up doing a lot of small allocations, parsing the json once and parsing the data structure afterwards). With a streaming parser, you can add the vertices to a contiguous array as they come in without paying the cost of creating the intermediate Json data structure. You have much fewer allocations since you write directly in the final data structure and you can be smart in how you will pre-allocate it.

I added added this directly into serialize::json rather than in its own library because it turns out I can reuse most of the existing code whereas maintaining a separate library (which I did originally) forces me to duplicate this code.

I wrote this trying to minimize the size of the patch so there may be places where the code could be nicer at the expenses of more changes (let me know what you prefer).

This is my first (potential) contribution to rust, so please let me know if I am doing something wrong (maybe I should have first introduced this proposition in the mailing list, or opened a github issue, etc.?). I work a few meters away from @pknfelix so I am not too hard to find :)
Fix typo
Remove extra semicolons
rustdoc: fix overly broad selectors
Suggested revisions to PR 13676.

Most important: distinguish function decl sugar for omitting `-> ()`
from type inference on closures.  I also tried to add a couple more
examples to further emphasize this distinction.  Note that this sugar
(of omitting `-> ()`) is actually already briefly mentioned in an
earlier section, so it is a little tricky deciding whether to put more
material here, or to move it up to the previous section.

Other drive-by fixes:

 * Fix the line length of the code blocks to fit in the width provided
   in the rendered HTML

 * Some minor revisions to wording (e.g. try to clarify in some cases
   where a type mismatch is arising).
auto merge of #13863 : huonw/rust/re-tweaks, r=pcwalton

Mostly code style e.g. avoiding `~` and using `for` + iterators.
Move bitflags module to libstd

This will allow us to provide type-safe APIs in libstd that are C-compatible.
Update for language changes