cc_binary(
name = "app",
srcs = glob([ "*.hpp", "*.cpp" ]),
)
A lot of work goes into those 4 lines. This is evidenced by the simple question of, how do you set up a custom compiler for that code properly? The answer being a couple hundred lines of starlark code, for what in other build systems is effectively `CC=clang` (to be fair bazel allows this but does not support or encourage it, especially for anything besides toy builds).
I like Bazel (a lot!) but you are oversimplifying it here.
Provided the abstraction doesn't leak I really don't care, in the same way that end users of Microsoft Word don't care about the algorithms that kern their text, about how DirectWrite does subpixel rendering, or anything else.
Yes, it's all fiercely large and complex. The original user is pointing out that this is all hidden for simple projects, waiting in the wings for when you need it, and therefore doesn't matter.
The author I was replying points out how simple the syntax is. But that's missing the point. I provided a direct counter example:
Adding a new compiler to bazel is very complicated, and by new compiler I include something as simple as asserting "all of my C++ code is c++17" at a project level is (when done the correct way, and not one of the many hacky prone to failure ways) a 100+ line toolchain definition (because C++17 should be treated as an entirely new compiler from the perspective of bazel; treating it as a command line argument gets you in a bad place where you hit weird errors).
To draw an analogy, it's like saying that C++ code like:
some_matrix[i, j];
Hello world is simple in python, but it is still hard to get started writing real-time code in it even if hello world might be your first step.
The issue is that declarative build systems ALWAYS need an escape hatch for the exceptions--and the exceptions grow over time.
We've been here before. It was called Make. And then it was called Ant. And then Maven. And Google still built their own system. And they will build another again.
Nobody ever learns the lesson that a build system is a program--period. Sorry to burst your bubble: there will be circular dependencies--you will have to deal with it. There will be two different C compilers on two different architectures. You will have to deal with it. Libraries will be in the wrong place--you will have to deal with it. These libraries come from the system but these libraries come from an artifact--you will have to deal with it.
The only way to deal with it is to have a genuine programming language underneath.
> there will be circular dependencies--you will have to deal with it.
Add them both to the same compilation unit (cc_library, whatever). Or extract an ABI (e.g. Turbine) and compile against that.
> There will be two different C compilers on two different architectures. You will have to deal with it.
Poke around https://github.com/tensorflow/tensorflow/tree/master/third_p... . I see arm and x86, Windows and many variants of Linux, multiple versions of GCC, multiple versions of clang, multiple versions of cuda, python 2 and 3, and names I don't even recognize.
See also https://docs.bazel.build/versions/master/platforms-intro.htm....
> Libraries will be in the wrong place--you will have to deal with it.
Just write the path to the file, or write a build rule that makes it visible in a standard location, or make it part of the platform definition, or use something like https://docs.bazel.build/versions/master/be/workspace.html#b... to alias it into your workspace. (Not recommended, but supported.)
> Libraries will be in the wrong place--you will have to deal with it.
Platform-specific library paths are very common. These days it's probably better specified as part of your "platform", but https://docs.bazel.build/versions/master/be/functions.html#s... is a convenient way to make in-place selectors.
I won't pretend bazel can express _everything_, but there's little you can't hack in _somehow_ with sufficient motivation, and moving towards the bazel-recommended patterns brings growing peace-of-mind (and faster builds).
(Disclaimer: Googler, work closely with the bazel team. I like bazel).
Gradle is in use on a couple billion LoC and still sucks.
Bazel is like so many other tools--it works great if it owns everything, but when it has to cooperate, it falls down hard.
> The only way to deal with it is to have a genuine programming language underneath.
I disagree. Having a full programming language is great for the flexibility, but it causes lots of issues at scale. Restrictions in Bazel are critical for having a good performance on a large codebase, and for keeping the codebase maintainable.
With restrictions, we can provide strong guarantees (e.g. determinism, hermeticity), get better tooling, we can query the graph (without running the tools), we can track all accesses to files, etc. We can also make large-scale changes across the codebase.
Note also that Bazel language is not truly declarative, but it encourages a separation between the declarations (BUILD files) and the logic (bzl files).
Note the vocabulary--"restrictions". Your build system isn't solving a technical problem--it's solving a political one and trying to cloak it in technical terms.
We already have a problem. Your build system is now IN THE WAY if I'm not at scale. Any build system that makes people take notice of it is an a priori failure.
Thanks for posting this though. I've had a nagging irritation with so many of these "scalable" things, and this is the first time it has really coalesced that "scale" is almost always intertwined with "political control".
$ cat Makefile
SRCS = foo.cpp bar.cpp baz.cpp
OBJS = $(SRCS:.cpp=.o)
PROG = app
EXT =
.PHONEY = all clean
all : $(PROG)
LDLIBS = $(OBJS)
$(PROG) : $(PROG:$(EXT)=.cc) $(OBJS)
clean :
rm -f $(PROG) $(OBJS)
$ make SRCS="`echo *.cpp`" clean all
rm -f app a.o b.o c.o
c++ -O2 -pipe -c a.cpp -o a.o
c++ -O2 -pipe -c b.cpp -o b.o
c++ -O2 -pipe -c c.cpp -o c.o
c++ -O2 -pipe app.cc a.o b.o c.o -o app
$The "beauty" of UNIX falls apart when trying to code across all of them.
For example, I cannot even remember if that Makefile would work 100% with a POSIX make.
Bazel isn't really nicer than the autotools when you need something complicated, if it even supports your platform. Here's a fun bazel bug report: https://github.com/bazelbuild/bazel/issues/4350#issuecomment...
I've always managed to avoid autotools unless it was used before with things like LDFLAGS='-lsocket -lns' make ...
* https://pubs.opengroup.org/onlinepubs/009695399/utilities/ma...
I _think_ that it's also broken, if I copy-paste it: your comment renders with spaces in the `clean :` stanza, but I believe make requires that to be a tab character?
While certainly simplistic, the bazel example shows one obscure feature (glob) that's both still fairly obvious, and unnecessary for a direct comparison to your example. The rest reads clean, and could be replicated/modified by someone with no clue fairly straightforwardly.
Don't get me wrong, bazel BUILD files will often hide a whole lot of magic. But the benefit is, for a newcomer the files they have to interact with on a day-to-day basis are friendly. Take tensorflow, one of the most complicated bazel repos I know - browse to a random leaf BUILD file and you'll probably find it quite readable. (I randomly clicked to https://github.com/tensorflow/tensorflow/blob/master/tensorf... , seems pretty clear - especially when I consider it's compiling kernels for GPUs, which I know nothing about.)
(Disclaimer: Googler, work closely with the bazel team. I like bazel.)
There's really not much cargo cult in my example. Everything would be in the most rudimentary doc or tutorial, certainly less reading than if you needed to use git for the first time.
And yes there is supposed to be a tab there, some copy-paste thing munged that.
What do you mean?
That makes the graph more granular, e.g. if you just update the foo_main.cc you don't need to recompile the libraries. Or you can reuse bar_lib in a different binary.
It could, in theory.
Something to be aware of though is that Bazel does do some stupid things around this space. Like adding and removing files causes the build rule to change (if using a glob), which will proc a full rebuild of the library.
Are you sure this is required? I just tried with a test repo and Bazel only performed two actions after I updated foo_main.cpp (compile foo_main.cpp and link app.)
Foo.cc that depends on a a lib that's glob of a.h, b.h, c.h, d.h.
Foo.cc that depends on a_lib, b_lib, etc.
Modify a. In the first case, you'll have to recompile all of abcd. In the second, only a.
Note that adding and removing files (including through a glob) does always cause a rebuild though (because it's a change of the rule). This is a deficiency of bazel.
The other nice thing is you get dead code elimination for free.
The other place this is obvious is with tests. If you have a unit test per source, a change to any source will return all tests, splitting reduces this.
In other words, correctly using bazel gives you access to all the cool magic linkers do without having to do the work to implement it. And it adds value even for the ones that do (like C++, again: you'll run fewer tests).
Bazel has other tools for mitigating excessive test running (like test size/time descriptions and parallel test running) running too many tests has never been a problem I have encountered with even my dozen source file bazel libraries. Bazel also has smart test runners that can split up the tests in a test binary and run it in parallel, and I don't have to write a dozen lines for every C++ library.
I'm literally quoting Google's best practices for using bazel/blaze.
> Bazel has other tools for mitigating excessive test running (like test size/time descriptions and parallel test running) running too many tests has never been a problem I have encountered with even my dozen source file bazel libraries. Bazel also has smart test runners that can split up the tests in a test binary and run it in parallel, and I don't have to write a dozen lines for every C++ library.
Right, but here's the key thing: You're still running the test. My way, you just don't, and you lose nothing. You use less CPU, and less time.
> To use fine-grained dependencies to allow parallelism and incrementality.
> To keep dependencies well-encapsulated.
Like if I need 5 source files in a library to keep it well encapsulated, I'm doing that instead of making 5 libraries that are a rat's nest of inter-dependencies. And like the headers and repeating all the deps and specific command line arguments and so on would be unreadable.
> Like if I need 5 source files in a library to keep it well encapsulated, I'm doing that instead of making 5 libraries that are a rat's nest of inter-dependencies.
If you can't form your dependency tree into a DAG, you have larger design issues. This is yet another thing that bazel does a good job of uncovering. Libraries with cyclic dependencies aren't well encapsulated, and you should refactor to remove that.
I recognize that at a small scale this doesn't matter. But to be frank, there are parts of my job that I literally would be unable to accomplish if my coworkers did what you suggest.
One source file per library and one source file per object is an example of two policies that will conflict here (and I'm not trading code organization for build organization when I can just as easily use the features intended for this situation).
Meanwhile in the real world limiting the accessibility of header files not meant for public use prevents people from depending on things they shouldn't. Organizing libraries on abstraction boundaries regardless of code organization allows for more flexible organization of code (e.g. for readability and documentation). And so on.
This is why these feature exists and why Google projects like both Tensorflow and Skia don't follow the practices you are espousing here pathologically.
> But to be frank, there are parts of my job that I literally would be unable to accomplish if my coworkers did what you suggest.
Then you are incompetent and bad at your job. To be blunt I would recommend firing an engineer who pathologically misused a build tool in ways that encourage hard to read code and difficult to document code, while also making the build bloated and more complicated, all in the name of barely existent (and not at all relevant) performance improvements. And then said they couldn't do their job unless everyone conformed to that myopic build pattern.
It's like what, an extra 4 characters to get the list of code files in a library from a bazel query? What in the world could you possibly be doing that having to iterate over five files rather than one makes your job impossible.
> Tensorflow
Tensorflow is a perenial special case at Google. It's a great tool, but it's consistent disregard for internal development practices is costly. A cost I've had to pay personally before.
> Then you are incompetent and bad at your job
No, I just don't have the time or interest in reimplement language analysis tools when I don't need to.
And I don't have the time or interest to do it by hand when bazel already has that.
I mean not really, it's there enough that for all practical cases it exists effectively. I would be extremely surprised if that wasn't intentional when any other C++ build tool makes use of it extensively. I would have laughed bazel out of the room if it didn't make use of the fact that nearly all C++ compilers provide nicely formatted lists of the files a given file depends on.
Also it does work for tests perfectly fine.
> Especially when its easier to have tooling automatically manage build files for you, so you don't even have to do it by hand!
And this managing build file tooling is public? Because I am not at all aware of any automatic tools for bazel along those lines.
Which really is my frustration with bazel's google developers, their views are eternally myopic about how other people use their tools (e.g. using C++17 properly means re-writing the whole toolchain from scratch, have fun!). Yet those views are based on a closed and mostly unpublished ecosystem.
Let alone how terrible bazel does with dynamic libraries on windows (each cc_library then outputs a dll! yay!).
I don't think you realize how for anyone outside of Google bazel's tagline might as well be "The best terrible option".
Well sure, but build systems are hard, so that's still success in my book.
> And this managing build file tooling is public
No, but neither is the language analysis stuff you suggest I build instead, and claim I'm incompetent if I don't do.
Yes, I get it, you have complaints about the tool. That doesn't make what I'm saying less correct.
Sure, but suggesting the one true way to use the tool is a way that only works inside of google's ecosystem is myopic. I don't actually have complaints with bazel directly. I have issues with the googlers who continue to insist on using it on a way that only works inside of google to others and then act surprised when those people don't use it at all (or use it wildly incorrectly, or complain about the tool being poorly thought out, and so on).
What you suggest runs counter to many of the things that makes Bazel useful for anyone outside of google. I would swap back to CMAKE, by hand makefiles, hell I would use shell scripts, before I use it the way you suggest.
> No, but neither is the language analysis stuff you suggest I build instead
I didn't say you specifically should go build that. I was saying it's possible with bazel, any language that doesn't have those features is not a mature programming language, and if bazel is going to be used with that language it should probably make use of those features (or accept that it's not a mature language). If C++ and javascript can provide reflection than so can whatever bespoke language you are describing.
> and claim I'm incompetent if I don't do.
No I claimed you are incompetent because you claimed you couldn't do you job if a `.lib` file contained the output from more than one source file.
None of the work I do cares about the actual output artifacts. I care, almost exclusively, about the representation of the build graph itself. That work cannot be done if I don't have a build graph to analyze, which I don't if you do things like glob files together.
I've seen the simple act of untangling a globbed dependency to the various isolated files reduce the size of an output artifact by gigabytes.
> any language that doesn't have those features is not a mature programming language
You're calling literally every language that doesn't use the c-linker an immature language. Which may include c++17-with-modules, though I don't know that for certain.
> javascript
Javascript doesn't do what you're talking about though. At least not if you do any fancy precompilation/tree-shaking to your js at compile time. If all you're doing is copying the files, then sure, but as soon as you want to do useful things like, for example, run a typescript or closure analysis on your files, or generate js from typescript, or compile and minify your js, it will get a whole heck of a lot faster when you use more isolated build targets[0]. I know because our JS teams went to a lot of work to make js builds faster by taking advantage of this information.
And I don't take issue with what are obviously exceptional cases. What you are describing is not "I put togeather 5 related files" it's like "I globbed a file I wasn't supposed to".
> You're calling literally every language that doesn't use the c-linker an immature language. Which may include c++17-with-modules, though I don't know that for certain.
Uhhhh, I don't think you understand how the feature in question functions. I am simply talking about the -M option family of gcc (and similar commands for other compilers). Which provides a dependency tree for C++ files.
> At least not if you do any fancy precompilation/tree-shaking to your js at compile time.
I think it's actually the opposite. Those are the same tools that provide the reflection features in question (or some other AST parsing library)... then you write a two line lambda and feed that in over an interpreter. Boom list of files.