# Snooping on code generation: @snoopc

@snoopc has the advantage of working on any modern version of Julia. It "snoops" on the code-generation phase of compilation (the 'c' is a reference to code-generation). Note that while native code is not cached, it nevertheless reveals which methods are being compiled.

Note that unlike @snoopi, @snoopc will generate all methods, not just the top-level methods that trigger compilation. (It is redundant to precompile dependent methods, but neither is it harmful.) It is also worth noting that @snoopc requires "spinning up" a new Julia process, and so it is a bit slower than @snoopi.

Let's demonstrate @snoopc with a snoop script, in this case for the ColorTypes package:

using SnoopCompile

### Log the compiles
# This only needs to be run once (to generate "/tmp/colortypes_compiles.log")

SnoopCompile.@snoopc "/tmp/colortypes_compiles.log" begin
using ColorTypes, Pkg
include(joinpath(dirname(dirname(pathof(ColorTypes))), "test", "runtests.jl"))
end

### Parse the compiles and generate precompilation scripts
# This can be run repeatedly to tweak the scripts

pc = SnoopCompile.parcel(reverse!(data[2]))
SnoopCompile.write("/tmp/precompile", pc)

As with @snoopi, the "/tmp/precompile" folder will now contain a number of *.jl files, organized by package. For each package, you could copy its corresponding *.jl file into the package's src/ directory and include it into the package as described for @snoopi.

There are more complete example illustrating potential options in the examples/ directory.

When calling the @snoopc macro, a new julia process is spawned using the function Base.julia_cmd(). Advanced users may want to tweak the flags passed to this process to suit specific needs. This can be done by passing an array of flags of the form ["--flag1", "--flag2"] as the first argument to the @snoopc macro. For instance, if you want to pass the --project=/path/to/dir flag to the process, to cause the julia process to load the project specified by the path, a snoop script may look like:
using SnoopCompile
# ... processing the precompile statements