This was the longest (in terms of line count) file in the project.
Splitting it up will save on compile time, as it did for TypeScript.
I observe a ~20sec speedup from `stack clean semantic && stack build semantic:lib`
Right now, Semantic.Version is recompiled on every invocation of
`stack build`, since we marked it as `-fforce-recomp` to ensure that
all deployments are tagged appropriately for haystack. However, this
entails a good deal of wasted time during development. With some
liberal application of `CPP`, we can make this recompilation only
happen on CI, thanks to the `release` flag and passing in a compiler
flag.
To test:
* apply the patch
* `stack build semantic`, then `stack exec semantic -- -v`. It should
print `semantic version 0.4.0 (<development>)`.
* `stack clean semantic && stack build --ghc-options=-DCOMPUTE_GIT_SHA`.
`stack exec semantic -- -v` should then print out the correct SHA.
Though it's probably not strictly necessary, I've marked the
`semantic` and `semanticd` executables to compile with
-DCOMPUTE_GIT_SHA, just in case.
Because we're getting serious about benchmarking in the run-up to
Windrose, it's time to bring in the `deepseq` package to ensure that
benchmarks can fully evaluate the result of a test case.
The `deepseq` package provides an `NFData` typeclass:
```
class NFData a where
rnf :: a -> ()
```
Instances use the `seq` combinator to ensure that the argument to
`rnf` is fully evaluated, returning (). If there is a `Generic`
instance for `a`, the implementation can be omitted. This patch adds
NFData for every syntax node, graph vertex, environment data
structures, and exceptions. It is long, but the work is very
straightforward, so don't panick.
The benchmark suite (`stack bench`) now produces more accurate
results. The benchmarks previously mimicked `rnf` by calling `show` on
the result of an evaluation or graph construction; now that we have
actual `NFData` instances we can use the `nfIO` combinator from
criterion. This has sped up the evaluation benchmarks and reduced
their memory consumption, while it has slowed down the call graph
benchmarks, as those benchmarks weren't evaluating the whole of the
graph.
Unfortunately, this patch increases compile times, as we have to
derive a few more Generic instances. I wish this weren't the case, but
there's little we can do about it now. In the future I have some plans
for how to reduce compile time, and I bet that those gains will at
least nullify the speed hit from this patch.
Now that we have NFData instances for every data type, we can start
benchmarking assignments, in preparation for fixing #2205.
This patch also pulls in updates to `effects` and `fastsum` that add
appropriate NFData instances for the data they vend.
Right now, when opening a shell with `script/ghci`, you can encounter
a tremendous slowdown by turning on pretty-printing (with `pretty`)
then printing any value (`[0..3]` should work).
This stems from the fact that our `.ghci` specifies the `prettyShow`
function, defined in Semantic.Util, as its `-interactive-print`
function. While this is a good choice of a pretty-printer, the fact
that it is in Util, a file which imports many modules and uses fancy
types, is not good: pretty-printing cannot begin until Util is
recompiled and linked in. This explains why benchmarking this slowdown
revealed nothing but `dlsym` calls: we thought it was due to linking
in the tree-sitter libraries, but it was actually waiting for Util to
compile and link in.
The fix is simple: define `prettyShow` in another module. This should
provide significant speedups to our developer workflow.
Prefixes on data constructors are generally an antipattern in Haskell:
if you're concerned about name collisions, have clients use qualified
imports for whatever modules they need. As such, this removes the T-
prefixes from the `Token` and `Context` types. This also renames
Context to Scope, which is a more exact and readable name.
I figure that since we're starting to show this to other teams, it
behooves our documentation to have a more meaningful description.
Happy to change this if y'all can come up with a snappier synopsis.
