<s>
Bazel	B-Application
(	O
)	O
is	O
a	O
free	B-Application
and	O
open-source	B-Application
software	I-Application
tool	O
used	O
for	O
the	O
automation	O
of	O
building	O
and	O
testing	O
software	O
.	O
</s>
<s>
Google	B-Application
uses	O
the	O
build	O
tool	O
Blaze	B-Application
internally	O
and	O
released	O
an	O
open-sourced	O
port	O
of	O
the	O
Blaze	B-Application
tool	O
as	O
Bazel	B-Application
,	O
named	O
as	O
an	O
anagram	O
of	O
Blaze	B-Application
.	O
</s>
<s>
Bazel	B-Application
was	O
first	O
released	O
in	O
March	O
2015	O
and	O
was	O
in	O
beta	O
status	O
by	O
September	O
2015	O
.	O
</s>
<s>
Similar	O
to	O
build	O
tools	O
like	O
Make	B-Application
,	O
Apache	B-Application
Ant	I-Application
and	O
Apache	B-Language
Maven	I-Language
,	O
Bazel	B-Application
builds	O
software	O
applications	O
from	O
source	O
code	O
using	O
a	O
set	O
of	O
rules	O
.	O
</s>
<s>
Rules	O
and	O
macros	O
are	O
created	O
in	O
the	O
Starlark	O
language	O
(	O
previously	O
called	O
Skylark	B-General_Concept
)	O
,	O
a	O
dialect	O
of	O
Python	B-Language
.	O
</s>
<s>
There	O
are	O
built-in	O
rules	O
for	O
building	O
software	O
written	O
in	O
Java	B-Language
,	O
C	B-Language
,	O
C++	B-Language
,	O
Go	B-Application
,	O
Python	B-Language
,	O
Objective-C	B-Language
,	O
and	O
bash	B-Device
scripts	O
.	O
</s>
<s>
Bazel	B-Application
can	O
produce	O
software	O
application	O
packages	O
suitable	O
for	O
deployment	O
for	O
the	O
Android	B-Application
and	O
iOS	B-Application
operating	B-General_Concept
systems	I-General_Concept
.	O
</s>
<s>
One	O
of	O
the	O
goals	O
of	O
Bazel	B-Application
is	O
to	O
create	O
a	O
build	O
system	O
where	O
build	O
target	O
inputs	O
and	O
outputs	O
are	O
fully	O
specified	O
and	O
therefore	O
precisely	O
known	O
to	O
the	O
build	O
system	O
.	O
</s>
<s>
To	O
achieve	O
a	O
more	O
accurate	O
dependency	O
graph	O
analysis	O
,	O
Bazel	B-Application
uses	O
content	B-Algorithm
digests	I-Algorithm
rather	O
than	O
file-based	O
timestamps	O
.	O
</s>
<s>
File	O
timestamps	O
are	O
commonly	O
used	O
to	O
detect	O
changes	O
in	O
tools	O
like	O
Make	B-Application
or	O
Apache	B-Application
Ant	I-Application
.	O
</s>
<s>
Another	O
Bazel	B-Application
's	O
goal	O
is	O
to	O
enable	O
distributed	O
and	O
parallel	O
builds	O
on	O
a	O
remote	O
cloud	O
infrastructure	O
.	O
</s>
<s>
Bazel	B-Application
provides	O
tooling	O
which	O
helps	O
developers	O
to	O
create	O
bit-identical	O
reproducible	O
build	O
outputs	O
.	O
</s>
<s>
Bazel	B-Application
's	O
implemented	O
rules	O
avoid	O
typical	O
pitfalls	O
such	O
as	O
embedding	O
timestamps	O
in	O
generated	O
outputs	O
to	O
ensure	O
content	O
digest	O
matches	O
.	O
</s>
<s>
Therefore	O
,	O
Bazel	B-Application
is	O
particularly	O
well-suited	O
for	O
larger	O
organizations	O
and	O
software	O
projects	O
that	O
have	O
a	O
significant	O
number	O
of	O
build	O
dependencies	O
.	O
</s>
<s>
Bazel	B-Application
is	O
extensible	O
with	O
its	O
custom	O
Starlark	O
programming	O
language	O
.	O
</s>
<s>
Starlark	O
uses	O
a	O
syntax	O
that	O
is	O
a	O
subset	O
of	O
the	O
syntax	O
of	O
the	O
Python	B-Language
programming	I-Language
language	I-Language
.	O
</s>
<s>
However	O
,	O
it	O
does	O
n't	O
implement	O
many	O
of	O
Python	B-Language
's	O
language	O
features	O
,	O
such	O
as	O
the	O
ability	O
to	O
mutate	O
collections	O
or	O
access	O
the	O
file	O
I/O	O
,	O
in	O
order	O
to	O
avoid	O
extensions	O
that	O
could	O
create	O
side-effects	O
or	O
create	O
build	O
outputs	O
not	O
known	O
to	O
the	O
build	O
system	O
itself	O
.	O
</s>
<s>
Bazel	B-Application
was	O
designed	O
as	O
a	O
multi-language	O
build	O
system	O
.	O
</s>
<s>
Examples	O
of	O
such	O
systems	O
include	O
Ant	B-Application
and	O
Maven	B-Language
for	O
Java	B-Language
,	O
Leiningen	B-Application
for	O
Clojure	B-Language
,	O
sbt	B-Language
for	O
Scala	B-Application
,	O
etc	O
.	O
</s>
<s>
Bazel	B-Application
also	O
provides	O
sandboxed	O
build	O
execution	O
.	O
</s>
<s>
Build	O
systems	O
most	O
similar	O
to	O
Bazel	B-Application
are	O
Pants	O
,	O
Buck	B-Application
,	O
and	O
Please	O
.	O
</s>
<s>
Pants	O
and	O
Buck	B-Application
both	O
aim	O
for	O
similar	O
technical	O
design	O
goals	O
as	O
Bazel	B-Application
and	O
were	O
inspired	O
by	O
the	O
Blaze	B-Application
build	O
system	O
used	O
internally	O
at	O
Google	B-Application
.	I-Application
</s>
<s>
Blaze	B-Application
is	O
also	O
the	O
predecessor	O
to	O
Bazel	B-Application
.	O
</s>
<s>
Bazel	B-Application
,	O
Pants	O
,	O
Buck	B-Application
,	O
and	O
Please	O
adopted	O
Starlark	O
as	O
a	O
BUILD	O
file	O
parser	O
,	O
respective	O
to	O
its	O
BUILD	O
file	O
syntax	O
.	O
</s>
<s>
One	O
of	O
the	O
key	O
features	O
that	O
differentiate	O
Bazel	B-Application
and	O
similar	O
systems	O
from	O
earlier	O
build	O
systems	O
is	O
the	O
use	O
of	O
a	O
sandbox	O
for	O
compilation	O
steps	O
.	O
</s>
<s>
When	O
Bazel	B-Application
performs	O
a	O
separate	O
compilation	O
,	O
it	O
creates	O
a	O
new	O
directory	O
and	O
fills	O
it	O
with	O
symlinks	O
to	O
the	O
explicit	O
input	O
dependencies	O
for	O
the	O
rule	O
.	O
</s>
<s>
For	O
languages	O
like	O
C/C	O
++	O
,	O
this	O
provides	O
a	O
significant	O
safety	O
net	O
for	O
the	O
inclusion	O
of	O
header	O
files	O
:	O
it	O
ensures	O
that	O
the	O
developer	O
is	O
aware	O
of	O
the	O
files	O
that	O
are	O
used	O
in	O
compilation	O
,	O
and	O
it	O
prevents	O
the	O
unexpected	O
inclusion	O
of	O
a	O
similarly	O
named	O
header	O
file	O
from	O
another	O
including	O
directory	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
builds	O
in	O
Bazel	B-Application
must	O
correct	O
the	O
compiled	O
objects	O
after	O
the	O
fact	O
,	O
trying	O
to	O
correct	O
path-related	O
issues	O
that	O
arose	O
from	O
the	O
sandbox	O
construction	O
using	O
flags	O
like	O
-fdebug-prefix-map	O
and	O
-oso_prefix	O
,	O
the	O
latter	O
having	O
become	O
available	O
in	O
Xcode	O
11.0	O
.	O
</s>
<s>
Since	O
Bazel	B-Application
's	O
initial	O
release	O
the	O
logo	O
was	O
a	O
green	O
letter	O
"	O
b	O
"	O
stylized	O
into	O
a	O
stem	O
of	O
a	O
basil	O
plant	O
with	O
two	O
leaves	O
.	O
</s>
<s>
On	O
July	O
5	O
,	O
2017	O
,	O
the	O
Bazel	B-Application
Blog	O
announced	O
a	O
new	O
logo	O
,	O
consisting	O
of	O
three	O
green	O
building	O
blocks	O
arranged	O
to	O
shape	O
a	O
heart	O
.	O
</s>
