Add line number if not a member

src/compiler/scala/tools/nsc/typechecker/RefChecks.scala

@@ -2085,22 +2085,25 @@ abstract class RefChecks extends Transform {
                       case _ => super.traverse(t)
                     }
                   case bind @ Bind(name, _) =>
+                    def richLocation(sym: Symbol): String = sym.ownsString match {
+                      case ""   => val n = sym.pos.line; if (n > 0) s"$sym at line $n" else sym.fullLocationString
+                      case owns => s"$sym in $owns"
+                    }
                     for (shade <- bind.getAndRemoveAttachment[PatShadowAttachment]) {
                       val shadowed = shade.shadowed
                       if (!absolved.contains(name) && !bind.symbol.hasTransOwner(shadowed.accessedOrSelf) && checkShadowed(shadowed)(selSym))
-                        refchecksWarning(bind.pos, s"Name $name is already introduced in an enclosing scope as ${shadowed.fullLocationString}. Did you intend to match it using backquoted `$name`?", WarningCategory.OtherShadowing)
+                        refchecksWarning(bind.pos, s"Name $name is already introduced in an enclosing scope as ${richLocation(shadowed)}. Did you intend to match it using backquoted `$name`?", WarningCategory.OtherShadowing)
 
                     }
                   case _ => super.traverse(t)
                 }
               }
               traverser.traverse(p)
             }
-            def checkAllCases(): Unit = for (cdef <- cases) check(cdef.pat, selectorSymbol)
             // check the patterns for unfriendly shadowing, patvars bearing PatShadowAttachment
             def checkShadowingPatternVars(): Unit =
               selector match {
-                // or for `(x, y) match case p(x, y) =>` check the corresponding args (whether they are aliases)
+                // or for `(x, y) match case p(x, y) =>` check the corresponding args
                 case treeInfo.Applied(Select(core, nme.apply), _, tupleArgs :: Nil) if isTupleSymbol(core.symbol.companion) =>
                   for (cdef <- cases)
                     cdef.pat match {
@@ -2110,11 +2113,13 @@ abstract class RefChecks extends Transform {
                         foreach2(args, tupleArgs)((arg, sel) => check(arg, notNull(sel.symbol)))
                       case p => check(p, selectorSymbol)
                     }
+                // or for `tp.dealiased match case tp =>` check `tp` if it looks like a derived value, but not `this.x` or `x.asInstanceOf`
                 case treeInfo.Applied(Select(core, _), _, _) if core.symbol != null && !core.symbol.isThisSym && selector.tpe <:< core.tpe.widen =>
                   for (cdef <- cases) check(cdef.pat, core.symbol)
-                case _ => checkAllCases()
+                case _ =>
+                  for (cdef <- cases) check(cdef.pat, selectorSymbol)
               }
-            checkShadowingPatternVars()
+            if (settings.warnPatternShadow) checkShadowingPatternVars()
             tree
           case _ => tree
         }

src/reflect/scala/reflect/internal/Symbols.scala

@@ -2719,6 +2719,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
                    isPrimaryConstructor))        ("primary constructor",  "constructor",     "PCTOR")
         else if (isClassConstructor)             ("constructor",          "constructor",     "CTOR")
         else if (isMethod)                       ("method",               "method",          "METH")
+        //else if (isValueParameter)               ("value parameter",      "parameter",       "VAL")
         else if (isTerm)                         ("value",                "value",           "VAL")
         else                                     ("",                     "",                "???")
 
@@ -2813,8 +2814,8 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
      *  for backward compatibility reasons.
      */
     def locationString: String = ownsString match {
-      case ""   => ""
-      case s    => " in " + s
+      case "" => ""
+      case s  => s" in $s"
     }
     def fullLocationString: String = toString + locationString
     def signatureString: String    = if (hasRawInfo) infoString(rawInfo) else "<_>"
@@ -2857,8 +2858,7 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
     }
 
     private def defStringCompose(infoString: String) = compose(
-      flagString,
-      keyString,
+      compose(flagString, keyString),
       varianceString + nameString + infoString + flagsExplanationString
     )
 
@@ -2877,8 +2877,9 @@ trait Symbols extends api.Symbols { self: SymbolTable =>
      */
     def defStringSeenAs(info: Type) = defStringCompose(infoString(info))
 
-    /** Concatenate strings separated by spaces */
-    private def compose(ss: String*) = ss filter (_ != "") mkString " "
+    /** Concatenate non-empty strings separated by a space. */
+    private def compose(x: String, y: String): String =
+      if (x.isEmpty) y else if (y.isEmpty) x else s"$x $y"
 
     def isSingletonExistential: Boolean =
       nme.isSingletonName(name)

test/files/neg/t11850.check

@@ -4,10 +4,10 @@ t11850.scala:9: warning: Name x is already introduced in an enclosing scope as v
 t11850.scala:28: warning: Name x is already introduced in an enclosing scope as value x in class CT. Did you intend to match it using backquoted `x`?
       case x   => 1     // warn
            ^
-t11850.scala:118: warning: Name x is already introduced in an enclosing scope as value x. Did you intend to match it using backquoted `x`?
+t11850.scala:118: warning: Name x is already introduced in an enclosing scope as value x at line 117. Did you intend to match it using backquoted `x`?
     case Y(x, y)  => x+y // only allow 1-1
            ^
-t11850.scala:118: warning: Name y is already introduced in an enclosing scope as value y. Did you intend to match it using backquoted `y`?
+t11850.scala:118: warning: Name y is already introduced in an enclosing scope as value y at line 117. Did you intend to match it using backquoted `y`?
     case Y(x, y)  => x+y // only allow 1-1
               ^
 t11850.scala:125: warning: Name self is already introduced in an enclosing scope as value self in class Selfie. Did you intend to match it using backquoted `self`?
@@ -16,12 +16,15 @@ t11850.scala:125: warning: Name self is already introduced in an enclosing scope
 t11850.scala:170: warning: Name _1 is already introduced in an enclosing scope as value _1 in class weird but true. Did you intend to match it using backquoted `_1`?
     case (_1, 27) => 3 // briefly did not warn as param name
           ^
-t11850.scala:187: warning: Name x is already introduced in an enclosing scope as value x. Did you intend to match it using backquoted `x`?
+t11850.scala:187: warning: Name x is already introduced in an enclosing scope as value x at line 186. Did you intend to match it using backquoted `x`?
     case x => x.toString
          ^
 t11850.scala:203: warning: Name c is already introduced in an enclosing scope as value c in class pattern matches occasionally appear in pattern-matching anonymous functions. Did you intend to match it using backquoted `c`?
   def f = c.collect { case c if c.flag => c.toString }
                            ^
+t11850.scala:212: warning: Name x is already introduced in an enclosing scope as object x in object is it worth qualifying what kind of term. Did you intend to match it using backquoted `x`?
+      case x   => 1
+           ^
 error: No warnings can be incurred under -Werror.
-8 warnings
+9 warnings
 1 error

test/files/neg/t11850.scala

@@ -202,3 +202,13 @@ class `pattern matches occasionally appear in pattern-matching anonymous functio
   val c = Collector()
   def f = c.collect { case c if c.flag => c.toString }
 }
+object `is it worth qualifying what kind of term` {
+  trait T
+  object x extends T
+
+  def f(t: T) =
+    t match {
+      case `x` => 0
+      case x   => 1
+    }
+}