fill out command line arguments

Author: steveklabnik

src/doc/rustc/src/command-line-arguments.md

@@ -4,54 +4,113 @@ Here's a list of command-line arguments to `rustc` and what they do.
 
 ## `-h`/`--help`: get help
 
+This flag will print out help information for `rustc`.
+
 ## `--cfg`: configure the compilation environment
 
-## `-L`: add a directory to the library search path.
+This flag can turn on or off various `#[cfg]` settings.
+
+## `-L`: add a directory to the library search path
+
+When looking for external crates, a directory passed to this flag will be searched.
 
 ## `-l`: link the generated crate to a native library
 
+This flag allows you to specify linking to a specific native library when building
+a crate.
+
 ## `--crate-type`: a list of types of crates for the compiler to emit
 
+This instructs `rustc` on which crate type to build.
+
 ## `--crate-name`: specify the name of the crate being built
 
+This informs `rustc` of the name of your crate.
+
 ## `--emit`: emit output other than a crate
 
+Instead of producing a crate, this flag can print out things like the assembly or LLVM-IR.
+
 ## `--print`: print compiler information
 
+This flag prints out various information about the compiler.
+
 ## `-g`: include debug information
 
+A synonym for `-C debug-level=2`.
+
 ## `-O`: optimize your code
 
+A synonym for `-C opt-level=2`.
+
 ## `-o`: filename of the output
 
+This flag controls the output filename.
+
 ## `--out-dir`: directory to write the output in
 
+The outputted crate will be written to this directory.
+
 ## `--explain`: provide a detailed explanation of an error message
 
+Each error of `rustc`'s comes with an error code; this will print
+out a longer explanation of a given error.
+
 ## `--test`: build a test harness
 
+When compiling this crate, `rustc` will ignore your `main` function
+and instead produce a test harness.
+
 ## `--target`: select a target triple to build
 
+This controls which [target](targets/index.html) to produce.
+
 ## `-W`: set lint warnings
 
+This flag will set which lints should be set to the [warn level](lints/levels.html#warn).
+
 ## `-A`: set lint allowed
 
+This flag will set which lints should be set to the [allow level](lints/levels.html#allow).
+
 ## `-D`: set lint denied
 
+This flag will set which lints should be set to the [deny level](lints/levels.html#deny).
+
 ## `-F`: set lint forbidden
 
+This flag will set which lints should be set to the [forbid level](lints/levels.html#forbid).
+
 ## `--cap-lints`: set the most restrictive lint level
 
+This flag lets you 'cap' lints, for more, [see here](lints/levels.html#capping-lints).
+
 ## `-C`/`--codegen`: code generation options
 
+This flag will allow you to set [codegen options](codegen-options/index.html).
+
 ## `-V`/`--verision`: print a version
 
+This flag will print out `rustc`'s version.
+
 ## `-v`/`--verbose`: use verbose output
 
+This flag, when combined with other flags, makes them produce extra output.
+
 ## `--extern`: specify where an external library is located
 
+This flag allows you to pass the name and location of an external crate that will
+be linked into the crate you're buildling.
+
 ## `--sysroot`: Override the system root
 
+The "sysroot" is where `rustc` looks for the crates that come with the Rust
+distribution; this flag allows that to be overridden.
+
 ## `--error-format`: control how errors are produced
 
-## `--color`: configur coloring of output
+This flag lets you control the format of errors.
+
+## `--color`: configur coloring of output
+
+This flag lets you control color settings of the output.