Expand Procedural Macro Docs

src/attributes.md

@@ -35,8 +35,7 @@ Attributes may appear as any of:
 
 _Inner attributes_, written with a bang ("!") after the hash ("#"), apply to the
 item that the attribute is declared within. _Outer attributes_, written without
-the bang after the hash, apply to the item or generic parameter that follow the
-attribute.
+the bang after the hash, apply to the thing that follows the attribute.
 
 Attributes may be applied to many things in the language:
 
@@ -82,6 +81,24 @@ fn some_unused_variables() {
 }
 ```
 
+There are three kinds of attributes:
+
+* Built-in attributes
+* Macro attributes
+* Derive mode helper attributes
+
+## Active and inert attributes
+
+An attribute is either active or inert. During attribute processing, *active
+attributes* remove themselves from the thing they are on while *inert attriutes*
+stay on.
+
+The `cfg` and `cfg_attr` attributes are active. The `test` attribute is inert
+when compiling for tests and active otherwise. Attribute macros are active.
+All other attributes are inert.
+
+---
+
 The rest of this page describes or links to descriptions of which attribute
 names have meaning.
 
@@ -161,14 +178,20 @@ which can be used to control type layout.
 
 - `macro_reexport` on an `extern crate` — re-export the named macros.
 
-- `macro_export` - export a macro for cross-crate usage.
+- `macro_export` - export a `macro_rules` macro for cross-crate usage.
 
 - `no_link` on an `extern crate` — even if we load this crate for macros, don't
   link it into the output.
 
 See the [macros section of the first edition of the
 book](../book/first-edition/macros.html#scoping-and-macro-importexport) for more
-information on macro scope.
+information on `macro_rules` macro scope.
+
+- `proc_macro` - Defines a [bang macro].
+
+- `proc_macro_derive` - Defines a [derive macro].
+
+- `proc_macro_attribute` - Defines an [attribute macro].
 
 ## Miscellaneous attributes
 
@@ -525,9 +548,11 @@ You can implement `derive` for your own traits through [procedural macros].
 [match expressions]: expressions/match-expr.html
 [external blocks]: items/external-blocks.html
 [items]: items.html
+[attribute macro]: procedural-macros.html#attribute-macros
+[bang macro]: procedural-macros.html#bang-macros
 [conditional compilation]: conditional-compilation.html
-[trait]: items/traits.html
-[main]: crates-and-source-files.html
+[derive macro]: procedural-macros.html#derive-macros
+[trait]: items/traits.html[main]: crates-and-source-files.html
 [`Termination`]: ../std/process/trait.Termination.html
 [where clause]: items/where-clauses.html
 [trait or lifetime bounds]: trait-bounds.html

src/conditional-compilation.md

@@ -84,6 +84,8 @@ The following configurations must be defined by the implementation:
   This can be used to enable extra debugging code in development but not in
   production.  For example, it controls the behavior of the standard library's
   `debug_assert!` macro.
+* `proc_macro` - Set when the crate being compiled is being compiled with the
+  `proc_macro` [crate type].
 
 You can also set another [attribute] based on a `cfg` variable with `cfg_attr`:
 
@@ -96,4 +98,5 @@ This is the same as `#[b]` if `a` is set by `cfg`, and nothing otherwise.
 Lastly, configuration options can be used in expressions by invoking the `cfg!`
 macro: `cfg!(a)` evaluates to `true` if `a` is set, and `false` otherwise.
 
-[attribute]: attributes.html
+[attribute]: attributes.html
+[crate type]: linkage.html

src/items/functions.md

@@ -134,7 +134,8 @@ fn test_only() {
 
 The attributes that have meaning on a function are [`cfg`], [`deprecated`],
 [`doc`], `export_name`, `link_section`, `no_mangle`, [the lint check
-attributes], [`must_use`], [the testing attributes], and [the optimization hint
+attributes], [`must_use`], [the procedural macro attributes], [the testing
+attributes], and [the optimization hint
 attributes].
 
 [external blocks]: items/external-blocks.html
@@ -147,6 +148,7 @@ attributes].
 [attributes]: attributes.html
 [`cfg`]: conditional-compilation.html
 [the lint check attributes]: attributes.html#lint-check-attributes
+[the procedural macro attributes]: procedural-macros.html
 [the testing attributes]: attributes.html#testing
 [the optimization hint attributes]: attributes.html#optimization-hints
 [`deprecated`]: attributes.html#deprecation

src/linkage.md

@@ -1,8 +1,11 @@
 # Linkage
 
-The Rust compiler supports various methods to link crates together both
+> Note: This section is described more in terms of the compiler than of
+> the language.
+
+The compiler supports various methods to link crates together both
 statically and dynamically. This section will explore the various methods to
-link Rust crates together, and more information about native libraries can be
+link crates together, and more information about native libraries can be
 found in the [FFI section of the book][ffi].
 
 [ffi]: ../book/ffi.html
@@ -35,7 +38,7 @@ be ignored in favor of only building the artifacts specified by command line.
 
 * `--crate-type=staticlib`, `#[crate_type = "staticlib"]` - A static system
   library will be produced. This is different from other library outputs in that
-  the Rust compiler will never attempt to link to `staticlib` outputs. The
+  the compiler will never attempt to link to `staticlib` outputs. The
   purpose of this output type is to create a static library containing all of
   the local crate's code along with all upstream dependencies. The static
   library is actually a `*.a` archive on linux and osx and a `*.lib` file on
@@ -44,28 +47,29 @@ be ignored in favor of only building the artifacts specified by command line.
   dynamic dependencies on other Rust code.
 
 * `--crate-type=cdylib`, `#[crate_type = "cdylib"]` - A dynamic system
-  library will be produced.  This is used when compiling Rust code as
+  library will be produced.  This is used when compiling
   a dynamic library to be loaded from another language.  This output type will
   create `*.so` files on Linux, `*.dylib` files on macOS, and `*.dll` files on
   Windows.
 
 * `--crate-type=rlib`, `#[crate_type = "rlib"]` - A "Rust library" file will be
   produced. This is used as an intermediate artifact and can be thought of as a
   "static Rust library". These `rlib` files, unlike `staticlib` files, are
-  interpreted by the Rust compiler in future linkage. This essentially means
+  interpreted by the compiler in future linkage. This essentially means
   that `rustc` will look for metadata in `rlib` files like it looks for metadata
   in dynamic libraries. This form of output is used to produce statically linked
   executables as well as `staticlib` outputs.
 
 * `--crate-type=proc-macro`, `#[crate_type = "proc-macro"]` - The output
   produced is not specified, but if a `-L` path is provided to it then the
   compiler will recognize the output artifacts as a macro and it can be loaded
-  for a program. If a crate is compiled with the `proc-macro` crate type it
-  will forbid exporting any items in the crate other than those functions
-  tagged `#[proc_macro_derive]` and those functions must also be placed at the
-  crate root. Finally, the compiler will automatically set the
-  `cfg(proc_macro)` annotation whenever any crate type of a compilation is the
-  `proc-macro` crate type.
+  for a program. Crates compiled with this crate type  must only export
+  [procedural macros]. The compiler will automatically set the `proc_macro`
+  [configuration option]. The crates are always compiled with the same target
+  that the compiler itself was built with. For example, if you are executing
+  the compiler from Linux with an `x86_64` CPU, the target will be
+  `x86_64-unknown-linux-gnu` even if the crate is a dependency of another crate
+  being built for a different target.
 
 Note that these outputs are stackable in the sense that if multiple are
 specified, then the compiler will produce each form of output at once without
@@ -124,7 +128,7 @@ dependencies will be used:
 
 In general, `--crate-type=bin` or `--crate-type=lib` should be sufficient for
 all compilation needs, and the other options are just available if more
-fine-grained control is desired over the output format of a Rust crate.
+fine-grained control is desired over the output format of a crate.
 
 ## Static and dynamic C runtimes
 
@@ -205,3 +209,6 @@ a statically linked binary on MSVC you would execute:
 ```ignore,notrust
 RUSTFLAGS='-C target-feature=+crt-static' cargo build --target x86_64-pc-windows-msvc
 ```
+
+[configuration option]: conditional-compilation.html
+[procedural macros]: procedural-macros.html