bpfmt fixes

Add error checking for calling CreateVariations with no variants

Running bpfmt or bpmodify on a Blueprints file that references
variables defined in a parent Blueprints file causes parse errors
on unknown variables.  Modify the parser to parse in two modes,
parser.Parse and parser.ParseAndEval.  The first parses without
attempting to evaluate variables and expressions, the second
performs a full evaluation.

Change-Id: Ic11948ea77c8e65379d7260591ada15db0e4f5b9

Trying to handle all the whitespace and newline printing inside
printToken got overly complicated, and resulted in a few bugs in
the layout around comments and indentation that were hard to fix.
Rewrite the whitespace and newline handling to be handled directly
by the object printers, using requestSpace() to ensure whitespace
is inserted and requestNewline() to ensure a newline is inserted.

Also fixes unnecessarily left aligning all comments that contain
indentation, and fixes accidentally unindenting comments that are
the last token in their indented block.

Change-Id: I18707802726107cf0b6ec7de9b542d0ec1d2c0dd

Calling CreateVariations with no variants will corrupt the
modules list with a module with nil logicModule, panic early
with a useful message instead.

Change-Id: Ic5c921efcba70c54efb5bb21a9626b2999376a69

Document subtle behavior in createVariations

Fix a bug in spliceModules and add tests

Add CONTRIBUTING.md file

createVariations relies on reusing the logicModule for the first
variant in order to replace the original module in the global module
map, which prevents leaving old split modules around in the global
module map.  Add comments to explain the behavior.

Change-Id: Ia06d7fa4bc777e807241996d4e8bf977e641d741

Fix typo

spliceModules was carefully reallocating the slice if necessary, and
then throwing away the reallocated slice and writing to the too-short
original slice.  Fix the bug, and add tests that would have caught it.

Change-Id: Ifc13b2025198b270c97097fd7d28cd36e460c98c

Add file to describe the procedure for submitting patches to
Blueprint.

Change-Id: I9601b5ab47e9d1230c2b3064a590d9eac1478433

Support for early mutators

"Variant" has been used to mean two slightly concepts in Blueprint.
The first and most obvious is a variant of a module, meaning a list
of all the ways that on version of a module differs from other
versions of the same modules, for example "arch:arm, link:static".
The other is for the specific way that a version of a module differs,
"arch:arm".

Rename all of uses of "variant" as the second meaning to "variation",
and update the documentation to clarify "variant" vs. "variation".
This modifies the build logic api to convert CreateVariants to
CreateVariations.

Change-Id: I789ef209ae6ddd39ec12e0c032f9f47f86698fe6

The mutators that run after dependencies are resolved can be too late
to support build logic that needs to vary the dependencies based on
the mutated axis, for example architecture.  This patch provides an
EarlyMutator interface that can be used to mutate modules before
any dependencies have been resolved.

In order for dependencies to be satisifed in a later pass, all
dependencies of a module must either have an identical variant,
must have a single variant, or must be inserted using
DynamicDependencyModuleContext.AddVariantDependency.

Change-Id: Ic6ae57e98edfd6c8c09a7788983128d3e4e992f0

Move actionDefs from moduleGroup to moduleInfo.  This will result
in multiple build.ninja headers for a single Blueprint file module
if it has multiple variants, each one specifying the variant
used to generate the following rules.

Change-Id: I414cd4d3266da8c2e92118b295569627ddf48cdd

Instead of iterating through groups and then iterating through the
group's modules, iterate through the modules directly.  This will
allow circular dependencies between groups as long as the individual
modules don't have circular dependencies.  In order to maintain the
ordering of modules in a group, each module is considered to have
an implicit dependency on any earlier modules in the same group.

Change-Id: Ibce67167c7234db70ede0a6b5c2b43fb8e0bb05d

Replace the array of mutator name/variant name pairs with
a map of mutator name to variant name, and store the string
variant name separately.

Change-Id: I181c2fcb05724c8755b90aaf866fdce9ef720b01

Move most of the contents of moduleGroup into moduleInfo.  This will
eventually reduce moduleGroup to a simple list of variants of the
same module.

Change-Id: I4289eb9953509751d7637558cd6db73373ccdf78

Forcing module names to be valid ninja names is an unnecessary
restraint on the project build logic.  Allow any string as a
module name, and sanitize and uniquify the module name for use
in module-scoped variables.

Also move the module scope to be per-module instead of per-group
so that modules can use the same local variable name for each variant.

Change-Id: If44cca20712305e2c0b6d6b39daa5eace335c148

Bugfixes

The cycle check can panic if the first call to check happens to land
on the first module in a cycle.  Print the cycle instead of panicking.

Change-Id: I6fc1c66dcc37b1eb6b11b9e65343452af3c8538d

If proptools.CopyProperties is passed two values that point same
slice then setting the destination slice to a new slice will
overwrite the source slice, and the properties struct that is both
the source and destination will have an empty slice.  Copy into
the new slice using a new reflect.Value, and then update the
destination.

Change-Id: I1bfcdc51e4278ea7c7ed81dafc928a5471219f05

Change-Id: I75875cbf60efc9aaf7c2df5709533c2c04b6fba4

New features

Miscellaneous bugfixes

Add overall Blueprint documentation

Variant errors can be introduced by Blueprints files, so print
a module error instead of panicing.

Switch back to:
moduleType {
    name: value,
    arch: {
        x86: {
            name: value,
        },
    },
}

This provides better consistency between properties defined at the
top level of a module and properties defined inside a map.

The parser will continue to support the other format for now, but the
printer will only produce the original format.

Change-Id: Ia9c5408b1b159843dbc57e2e480ca2972598186d

Add support for + operator on maps.  The semantics are that keys that
exist in both maps are added with the + operator, and keys that exist
in one map are copied to the resulting map.

Change-Id: Iba9a6f886477a1eb7311272d07944800c806e368

Change-Id: I271db2120aba1a5c99f21198f1eff6370e6e2389

Support += assignments to variables.  Variables are now mutable
up until they are referenced, then they become immutable.  This
will allow variables to be modified in a conditional, or allow
better commenting on why parts of a variable are set.

Change-Id: Iad964da7206b493365fe3686eedd7954e6eaf9a2

The printer was allowing extra newlines in odd places, for example
between a property name and the '=' in a module definition.  Make
newline location stricter by explicitly allowing newlines or
line comments.

generateModuleBuildActions was continuing to call GenerateBuildActions
on all modules even after one returned an error.  This could cause a
later module to panic because it was missing information that was
supposed to be generated by the module that returned an error, hiding
the earlier error message.

If a module returns an error, stop triggering any new goroutines to
call GenerateBuildActions on later modules.

If .ninja_log contains an entry that used to be a file but is now a
non-empty directory the os.Remove call will fail.  Silently ignore
this error, if the files in the directory are abandoned the directory
will be cleaned up when the files are removed.