Refinements to soft modifiers

 - also handle parameter modifiers
 - add a spec

Author: odersky

compiler/src/dotty/tools/dotc/parsing/Parsers.scala

@@ -1955,7 +1955,8 @@ object Parsers {
             }
         }
         else {
-          if (isIdent(nme.`inline`)) mods = addModifier(mods)
+          if (isIdent(nme.`inline`) && in.isSoftModifierInParamModifierPosition)
+            mods = addModifier(mods)
           mods = atPos(start) { mods | Param }
         }
         atPos(start, nameStart) {
@@ -2614,7 +2615,7 @@ object Parsers {
           if (in.token == IMPLICIT || in.token == ERASED) {
             val start = in.offset
             var imods = modifiers(funArgMods)
-            if (isBindingIntro && !isIdent(nme.`inline`))
+            if (isBindingIntro)
               stats += implicitClosure(start, Location.InBlock, imods)
             else
               stats +++= localDef(start, imods)

compiler/src/dotty/tools/dotc/parsing/Scanners.scala

@@ -742,6 +742,9 @@ object Scanners {
     def isSoftModifierInModifierPosition: Boolean =
       isSoftModifier && inModifierPosition()
 
+    def isSoftModifierInParamModifierPosition: Boolean =
+      isSoftModifier && !lookaheadIn(BitSet(COLON))
+
 // Literals -----------------------------------------------------------------
 
     private def getStringLit() = {

docs/docs/reference/inline.md

@@ -3,8 +3,7 @@ layout: doc-page
 title: Inline
 ---
 
-`inline` is a new modifier that guarantees that a definition will be
-inline at the point of use. Example:
+`inline` is a new [soft modifier](./soft-modifier.html) that guarantees that a definition will be inline at the point of use. Example:
 
     object Config {
       inline val logging = false

docs/docs/reference/opaques.md

@@ -53,4 +53,6 @@ But the following operations would lead to type errors:
   l / l2                  // error: `/` is not a member fo Logarithm
 ```
 
+`opaque` is a [soft modifier](./soft-modifier.html).
+
 For more details, see [Scala SIP 35](https://docs.scala-lang.org/sips/opaque-types.html).

tests/pos/i5145.scala

@@ -5,4 +5,12 @@ class Test {
     opaque(3)
     inline
   }
+  def bar(inline: Int => Int) = 3
+  inline def baz(inline x: Int => Int) = 3
+
+  locally {
+    bar(inline = identity)
+    bar(inline => inline)
+    bar(implicit inline => inline)
+  }
 }