Fixes format strings in assertions. Fixes #540 (#542)

1 files changed, 7 insertions, 4 deletions

diff --git a/chiselFrontend/src/main/scala/chisel3/core/Assert.scala b/chiselFrontend/src/main/scala/chisel3/core/Assert.scala
index 7f67f244..43a74192 100644
--- a/chiselFrontend/src/main/scala/chisel3/core/Assert.scala
+++ b/chiselFrontend/src/main/scala/chisel3/core/Assert.scala
@@ -23,9 +23,10 @@ object assert { // scalastyle:ignore object.name
     * and single reset).
     *
     * @param cond condition, assertion fires (simulation fails) when false
-    * @param message optional message to print when the assertion fires
+    * @param message optional format string to print when the assertion fires
     * @param data optional bits to print in the message formatting
     *
+    * @note See [[printf.apply(fmt:String* printf]] for format string documentation
     * @note currently cannot be used in core Chisel / libraries because macro
     * defs need to be compiled first and the SBT project is not set up to do
     * that
@@ -51,12 +52,14 @@ object assert { // scalastyle:ignore object.name
   }
 
   def apply_impl_do(cond: Bool, line: String, message: Option[String], data: Bits*)(implicit sourceInfo: SourceInfo, compileOptions: CompileOptions) {
+    val escLine = line.replaceAll("%", "%%")
     when (!(cond || Module.reset.toBool)) {
       val fmt = message match {
-        case Some(str) => s"Assertion failed: $str\n    at $line\n"
-        case None => s"Assertion failed\n    at $line\n"
+        case Some(msg) =>
+          s"Assertion failed: $msg\n    at $escLine\n"
+        case None => s"Assertion failed\n    at $escLine\n"
       }
-      printf.printfWithoutReset(fmt.replaceAll("%", "%%"), data:_*)
+      printf.printfWithoutReset(fmt, data:_*)
       pushCommand(Stop(sourceInfo, Node(Builder.forcedClock), 1))
     }
   }