Add custom mdoc modifier for emitted Verilog (#1666)

4 files changed, 89 insertions, 34 deletions

diff --git a/docs/README.md b/docs/README.md
index 0ebcd23a..dfc7f934 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -1,4 +1,4 @@
-# chisel3/docs/README.md
+# Chisel 3 Documentation
 
 This directory contains documentation on the code within this repository.
 Documents can either be written directly in markdown, or
@@ -26,8 +26,52 @@ Our documentation strategy for this repository is as follows:
  * Old documentation is contained in the `src/wiki-deprecated` directory and is being incrementally converted to these
  categories.
 
-To build the documentation, run `docs/mdoc` from SBT in the root directory. The generated documents
+This documentation is hosted on the Chisel [website](https://www.chisel-lang.org).
+
+## mdoc
+
+### Basic Use
+
+To build the documentation, run `docs/mdoc` via SBT in the root directory. The generated documents
 will appear in the `docs/generated` folder. To iterate on the documentation, you can run `docs/mdoc --watch`. For
 more `mdoc` instructions you can visit their [website](https://scalameta.org/mdoc/).
 
-This documentation is hosted on the Chisel [website](https://www.chisel-lang.org).
+### Custom `verilog` modifier
+
+mdoc supports [custom modifiers](https://scalameta.org/mdoc/docs/modifiers.html#postmodifier).
+We have created a custom `verilog` modifier to enable displaying the Verilog output of Chisel.
+
+Example use:
+````
+```scala mdoc:silent
+class MyModule extends RawModule {
+  val in = IO(Input(UInt(8.W)))
+  val out = IO(Output(UInt(8.W)))
+  out := in + 1.U
+}
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new MyModule)
+```
+````
+The `verilog` modifier tells mdoc to run the Scala block, requiring that each Statement returns a String.
+It will then concatenate the resulting Strings and wrap them in triple backticks with the language set to `verilog`:
+````
+```scala
+class MyModule extends RawModule {
+  val in = IO(Input(UInt(8.W)))
+  val out = IO(Output(UInt(8.W)))
+  out := in + 1.U
+}
+```
+```verilog
+module MyModule(
+  input  [7:0] in,
+  output [7:0] out
+);
+  assign out = in + 8'h1; // @[main.scala 9:13]
+endmodule
+```
+````
+
+Note that `imports` are okay in `mdoc:verilog` blocks, but any utility Scala code should be in a separate block.
diff --git a/docs/src/cookbooks/naming.md b/docs/src/cookbooks/naming.md
index 4caabaff..098ea898 100644
--- a/docs/src/cookbooks/naming.md
+++ b/docs/src/cookbooks/naming.md
@@ -5,7 +5,6 @@ section: "chisel3"
 ---
 
 ```scala mdoc:invisible
-import chisel3.internal.plugin._
 import chisel3._
 import chisel3.experimental.prefix
 import chisel3.experimental.noPrefix
@@ -57,8 +56,9 @@ class ExampleNoPrefix extends MultiIOModule {
 
   out := add
 }
-
-println(ChiselStage.emitVerilog(new ExampleNoPrefix))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new ExampleNoPrefix)
 ```
 
 ### I am still not getting the name I want. For example, inlining an instance changes my name!
@@ -88,8 +88,9 @@ class MyLeaf extends MultiIOModule {
   val out = IO(Output(UInt(3.W)))
   out := in
 }
-
-println(ChiselStage.emitVerilog(new WrapperExample))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new WrapperExample)
 ```
 
 This can be used to rename instances and non-aggregate typed signals.
diff --git a/docs/src/explanations/bundles-and-vecs.md b/docs/src/explanations/bundles-and-vecs.md
index 0c8a77b3..dcac31cd 100644
--- a/docs/src/explanations/bundles-and-vecs.md
+++ b/docs/src/explanations/bundles-and-vecs.md
@@ -103,10 +103,10 @@ class MyFlippedModule extends RawModule {
 
 This generates the following Verilog:
 
-```scala mdoc
+```scala mdoc:verilog
 import chisel3.stage.ChiselStage
 
-println(ChiselStage.emitVerilog(new MyFlippedModule()))
+ChiselStage.emitVerilog(new MyFlippedModule())
 ```
 
 ### MixedVec
diff --git a/docs/src/explanations/naming.md b/docs/src/explanations/naming.md
index a626b878..fb1121f9 100644
--- a/docs/src/explanations/naming.md
+++ b/docs/src/explanations/naming.md
@@ -17,10 +17,9 @@ systemic name-stability issues, please refer to the naming [cookbook](../cookboo
 ### Compiler Plugin
 
 ```scala mdoc
-import chisel3.internal.plugin._
+// Imports used by the following examples
 import chisel3._
-import chisel3.experimental.prefix
-import chisel3.experimental.noPrefix
+import chisel3.experimental.{prefix, noPrefix}
 import chisel3.stage.ChiselStage
 ```
 
@@ -28,6 +27,7 @@ With the release of Chisel 3.4, users should add the following line to their bui
 naming:
 
 ```scala
+// chiselVersion is the String version (eg. "3.4.0")
 addCompilerPlugin("edu.berkeley.cs" % "chisel3-plugin" % chiselVersion cross CrossVersion.full)
 ```
 
@@ -48,7 +48,9 @@ class Example1 extends MultiIOModule {
   val io = IO(new MyBundle())
   // val io = autoNameRecursively("io")(IO(new MyBundle()))
 }
-println(ChiselStage.emitVerilog(new Example1))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example1)
 ```
 
 Otherwise, it is rewritten to also include the name as a prefix to any signals generated while executing the right-hand-
@@ -70,8 +72,9 @@ class Example2 extends MultiIOModule {
 
   out := add + 1.U
 }
-
-println(ChiselStage.emitVerilog(new Example2))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example2)
 ```
 
 Note that the naming also works if the hardware type is nested in an `Option` or a subtype of `Iterable`:
@@ -92,8 +95,9 @@ class Example3 extends MultiIOModule {
 
   out := opt.get + 1.U
 }
-
-println(ChiselStage.emitVerilog(new Example3))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example3)
 ```
 
 There is also a slight variant (`autoNameRecursivelyProduct`) for naming hardware with names provided by an unapply:
@@ -105,9 +109,11 @@ class UnapplyExample extends MultiIOModule {
 
   out := in
 }
-
-println(ChiselStage.emitVerilog(new UnapplyExample))
 ```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new UnapplyExample)
+```
+
 Note that the compiler plugin will not insert a prefix in these cases because it is ambiguous what the prefix should be.
 Users who desire a prefix are encouraged to provide one as [described below](#prefixing).
 
@@ -137,11 +143,11 @@ class Example5 extends MultiIOModule {
 
   out := prefix("ECO") { add + 1.U + in }
 }
-
-println(ChiselStage.emitVerilog(new Example4))
-println(ChiselStage.emitVerilog(new Example5))
-
-``` 
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example4)
+ChiselStage.emitVerilog(new Example5)
+```
 
 Also note that the prefixes append to each other (including the prefix generated by the compiler plugin):
 
@@ -154,8 +160,9 @@ class Example6 extends MultiIOModule {
 
   out := add
 }
-
-println(ChiselStage.emitVerilog(new Example6))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example6)
 ```
 
 Sometimes you may want to disable the prefixing. This might occur if you are writing a library function and
@@ -170,8 +177,9 @@ class Example7 extends MultiIOModule {
 
   out := add
 }
-
-println(ChiselStage.emitVerilog(new Example7))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example7)
 ```
 
 ### Suggest a Signal's Name (or the instance name of a Module)
@@ -188,8 +196,9 @@ class Example8 extends MultiIOModule {
 
   out := add
 }
-
-println(ChiselStage.emitVerilog(new Example8))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example8)
 ```
 
 ### Set a Module Name
@@ -208,9 +217,10 @@ class Example9(width: Int) extends MultiIOModule {
 
   out := add
 }
-
-println(ChiselStage.emitVerilog(new Example9(8)))
-println(ChiselStage.emitVerilog(new Example9(1)))
+```
+```scala mdoc:verilog
+ChiselStage.emitVerilog(new Example9(8))
+ChiselStage.emitVerilog(new Example9(1))
 ```
 
 ### Reflection Naming