generate compile_commands.json. why not.

build.sbt

@@ -14,6 +14,7 @@ lazy val root = (project in file("."))
       "org.scalatest"     %% "scalatest"  % "3.2.18" % "test",
       "edu.berkeley.cs"   %% "chiseltest" % "6.0.0",
       "com.github.scopt"  %% "scopt"      % "4.1.0",
+      "com.lihaoyi"       %% "upickle"    % "3.1.0",
     ),
     scalacOptions ++= Seq(
       "-language:reflectiveCalls", "-deprecation", "-feature", "-Xcheckinit",

src/main/scala/ee/hrzn/chryse/tasks/BaseTask.scala

@@ -61,12 +61,13 @@ abstract class BaseTask {
   }
 
   case class CompilationUnit(
-      val inPaths: Seq[String],
+      val primaryInPath: Option[String],
+      val otherInPaths: Seq[String],
       val outPath: String,
       val cmd: Seq[String],
   ) {
     val digestPath            = s"$outPath.dig"
-    private val sortedInPaths = inPaths.sorted
+    private val sortedInPaths = otherInPaths.appendedAll(primaryInPath).sorted
 
     private def addIntToDigest(n: Int)(implicit digest: MessageDigest): Unit =
       digest.update(String.format("%08x", n).getBytes("UTF-8"))
@@ -85,8 +86,8 @@ abstract class BaseTask {
 
     private def digestInsWithCmd(): String = {
       implicit val digest = MessageDigest.getInstance("SHA-256")
-      addIntToDigest(inPaths.length)
-      for { inPath <- inPaths.sorted } {
+      addIntToDigest(sortedInPaths.length)
+      for { inPath <- sortedInPaths } {
         addStringToDigest(inPath)
         addBytesToDigest(Files.readAllBytes(Paths.get(inPath)))
       }

src/main/scala/ee/hrzn/chryse/tasks/BuildTask.scala

@@ -38,7 +38,8 @@ object BuildTask extends BaseTask {
     )
 
     val yosysCu = CompilationUnit(
-      Seq(verilogPath, yosysScriptPath),
+      Some(verilogPath),
+      Seq(yosysScriptPath),
       jsonPath,
       Seq(
         "yosys",
@@ -57,7 +58,8 @@ object BuildTask extends BaseTask {
 
     val ascPath = s"$buildDir/$name-${platform.id}.asc"
     val ascCu = CompilationUnit(
-      Seq(jsonPath, pcfPath),
+      Some(jsonPath),
+      Seq(pcfPath),
       ascPath,
       Seq(
         platform.nextpnrBinary,
@@ -76,7 +78,8 @@ object BuildTask extends BaseTask {
 
     val binPath = s"$buildDir/$name-${platform.id}.bin"
     val binCu = CompilationUnit(
-      Seq(ascPath),
+      Some(ascPath),
+      Seq(),
       binPath,
       Seq(platform.packBinary, ascPath, binPath),
     )

src/main/scala/ee/hrzn/chryse/tasks/CxxsimTask.scala

@@ -92,6 +92,7 @@ object CxxsimTask extends BaseTask {
     )
 
     val yosysCu = CompilationUnit(
+      None,
       Seq(blackboxIlPath, verilogPath, yosysScriptPath),
       ccPath,
       Seq(
@@ -143,12 +144,21 @@ object CxxsimTask extends BaseTask {
       cc <- ccs
       obj = buildPathForCc(cc)
       cmd = compileCmdForCc(cc, obj)
-    } yield CompilationUnit(Seq(cc) ++ headers, obj, cmd)
+    } yield CompilationUnit(Some(cc), headers, obj, cmd)
 
     runCus("compilation", cus)
 
+    val cwd = System.getProperty("user.dir")
+    writePath(s"$buildDir/compile_commands.json") { wr =>
+      upickle.default.writeTo(
+        cus.map(cu => ClangdEntry(cwd, cu.primaryInPath.get, cu.cmd)),
+        wr,
+      )
+    }
+
     val binPath = s"$buildDir/$name"
     val linkCu = CompilationUnit(
+      None,
       cus.map(_.outPath),
       binPath,
       Seq("c++", "-o", binPath) ++ cxxOpts ++ cus.map(_.outPath),
@@ -177,3 +187,9 @@ object CxxsimTask extends BaseTask {
       .map(_.toString)
       .filter(_.endsWith(ext))
 }
+
+private case class ClangdEntry(directory: String, file: String, arguments: Seq[String])
+private object ClangdEntry {
+  implicit val rw: upickle.default.ReadWriter[ClangdEntry] =
+    upickle.default.macroRW
+}