Update documentation for out-of-tree use

Author: jacobdweightman

zirgen/docs/01_Getting_Started.md

@@ -1,52 +1,128 @@
 # Getting Started
 
 We don't currently release Zirgen in any packaged form, so it's only available
-through this repository. Assuming you've cloned and built things from this repo
-before, building Zirgen with Bazel is simple with the following command. Note,
-though, that this isn't strictly necessary, and that Bazel will automatically
-(re)build Zirgen if you use it to invoke the tests as well.
+through this repository. This guide assumes you're using Bazel as your build
+system, and want to use Zirgen "out of tree" from a separate project.
 
+
+# Project structure
+
+## Pulling in the Zirgen compiler
+
+From a fresh project directory, we're going to need to create three build
+configuration files. First, create a `.bazelrc` file, and put the following two
+lines in it. These are necessary to ensure MLIR, one of Zirgen's dependencies,
+compiles correctly.
 ```
-bazel build //zirgen/dsl:zirgen
+build --cxxopt=-std=c++17
+build --host_cxxopt=-std=c++17
 ```
 
-## Hello world!
+Second, we need to pin our Bazel version. Zirgen is currently built with Bazel
+6.0, so we recommend creating a `.bazelversion` file with the following content.
+If you want to use a different version of Bazel for any reason, your mileage may
+vary.
+```
+6.0.0
+```
 
-Following in the footsteps of our forebears, let's take a look at a classic
-"Hello world" program. This program is already available as a test and example,
-so we can run it with the following command from the root of this repository:
+Third, create a `WORKSPACE` file. This is a Bazel configuration file that deals
+with "global" configurations like project dependencies, and this is where we're
+going to define how to pull in the Zirgen compiler:
+```
+workspace(name = "zirgen-oot")
+
+load("@bazel_tools//tools/build_defs/repo:git.bzl", "git_repository")
+
+git_repository(
+    name = "zirgen",
+    branch = "main", # feel free to pin a particular commit instead for stability!
+    remote = "https://github.com/risc0/zirgen.git",
+)
+
+load("@zirgen//bazel/rules/zirgen:deps.bzl", "zirgen_dependencies")
+zirgen_dependencies()
+
+# configure transitive dependencies
+load("@bazel_skylib//:workspace.bzl", "bazel_skylib_workspace")
+bazel_skylib_workspace()
+
+load("@llvm-raw//utils/bazel:configure.bzl", "llvm_configure")
+llvm_configure(name = "llvm-project")
+```
 
+At this point, it should be possible to build the Zirgen compiler, which might
+take a few minutes but only needs to be done once:
 ```
-$ bazel run //zirgen/dsl:zirgen -- $(pwd)/zirgen/dsl/test/hello_world.zir --test
-...
-Running 0
-[0] Log: Hello world!
-Lookups resolved
+bazel build @zirgen//zirgen/dsl:zirgen
 ```
 
-This command passes two arguments to the Zirgen executable. The first,
-`$(pwd)/zirgen/dsl/test/hello_world.zir`, specifies the path of the Zirgen file
-we want to run on. The second, `--test`, specifies that we want to run all the
-tests defined in the file we're running. Typically, the output of Zirgen is a
-generated Rust or C++ library that then needs to be integrated with the RISC
-Zero proof system. For the sake of simplicity here and as a useful practice
-during the development, it is easiest to experiment with Zirgen by writing tests
-alongside your circuit code, which can be run in the builtin interpreter without
-doing this integration work using the `--test` option. Now, the important part
-of the file is the following:
+## Setting up your new circuit
 
+Now that the compiler is set up, we just need to start the new circuit. Create a
+new directory called `circuit`; the name is not important, but consistency is
+key! In this directory, create a new file called `circuit.zir`, and include the
+following code:
 ```
-test {
-  Log("Hello world!");
+test Hello {
+    Log("Hello world!");
 }
 ```
 
-The keyword `test` declares that the thing that follows (enclosed in curly
-braces) is a test. Tests can be given an optional name, but if they aren't named
-then they are labeled with sequential numbers. This causes the text "Running 0"
-to be written to stdout, marking the beginning of the execution of that test.
-The statement `Log("Hello world!");` is what causes the text "[0] Log: Hello
-world!" to be written to stdout.
+Next, add a `BUILD.bazel` file in the same directory, and add the following to
+it to configure a new build rule that generates Rust code for the circuit.
+```
+load("@zirgen//bazel/rules/zirgen:dsl-defs.bzl", "zirgen_genfiles")
+
+filegroup(
+    name = "imports",
+    srcs = glob(["*.zir"]),
+)
+
+zirgen_genfiles(
+    name = "CircuitIncs",
+    zir_file = ":circuit.zir",
+    data = [":imports"],
+    zirgen_outs = [
+        (
+            ["--emit=rust"],
+            "circuit.rs.inc",
+        ),
+    ],
+)
+```
+
+## Hello world!
+
+Now with everything set up, we're ready to run the new circuit. The output of
+the Zirgen compiler is generated code that can then be called by 0STARK to
+generate real proofs. Our circuit is so trivial that there's not really much to
+generate, but it can be done with the following Bazel command, which will place
+the code in the Bazel build directory:
+```
+bazel build //circuit:GenerateCircuitIncs
+```
+
+Of more immediate interest, it's also possible to test and debug circuits using
+a built-in interpreter. This doesn't generate real proofs, but it does make it
+easy to try things out as you go along. To run our circuit in the interpreter:
+```
+bazel run @zirgen//zirgen/dsl:zirgen -- $(pwd)/circuit/circuit.zir --test
+```
+> ```
+> Running Hello
+> [0] Log: Hello world!
+> Lookups resolved
+> Verifying constraints for Hello
+> Verifying zll constraints for Hello
+> ```
+
+This command invokes the Zirgen compiler through Bazel. Everything after `--` is
+passed directly to the `zirgen` executable as a command line option: the first
+argument indicates the "main" file of the circuit. The `--test` indicates that
+all the tests in the source code should be run in the interpreter. In this case,
+our code has one test named `Hello`, and it logs the string "Hello world!" on
+cycle zero. And presto! We've set up, written, and run a brand-new circuit!
 
 [Prev](README.md)
 [Next](02_Conceptual_Overview.md)

zirgen/docs/03_Building_a_Fibonacci_Circuit.md

@@ -19,7 +19,7 @@ component Top() {}
 ```
 
 Next, we need to tell Bazel about our new circuit, and tell it how to build our
-project. Create a `Build.bazel` file in the same directory as our new circuit
+project. Create a `BUILD.bazel` file in the same directory as our new circuit
 source file, with these contents:
 
 ```