cleanups for underscores in tuple unpacking

compiler/lexer.nim

@@ -868,9 +868,14 @@ proc rawGetTok*(L: var TLexer, tok: var TToken) =
       tok.tokType = tkAccent
       inc(L.bufpos)
     of '_':
+      inc(L.bufpos)
+      if L.buf[L.bufpos] notin SymChars:
         tok.tokType = tkSymbol
         tok.ident = getIdent("_")
-      inc(L.bufpos)
+      else:
+        tok.literal = $c
+        tok.tokType = tkInvalid
+        lexMessage(L, errInvalidToken, c & " (\\" & $(ord(c)) & ')')
     of '\"':
       # check for extended raw string literal:
       var rawMode = L.bufpos > 0 and L.buf[L.bufpos-1] in SymChars

compiler/semstmts.nim

@@ -369,9 +369,10 @@ proc addToVarSection(c: PContext; result: var PNode; orig, identDefs: PNode) =
   else:
     result.add identDefs
 
-proc isDiscardUnderscore(n: PNode): bool =
+proc isDiscardUnderscore(v: PSym): bool =
-  if n.kind != nkIdent: return false
+  if v.name.s == "_":
-  return n.ident.s == "_"
+    v.flags.incl(sfGenSym)
+    result = true
 
 proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
   var b: PNode
@@ -436,10 +437,8 @@ proc semVarOrLet(c: PContext, n: PNode, symkind: TSymKind): PNode =
 
     for j in countup(0, length-3):
       var v = semIdentDef(c, a.sons[j], symkind)
-      if sfGenSym notin v.flags and
+      if sfGenSym notin v.flags and not isDiscardUnderscore(v):
-         not isDiscardUnderscore(a.sons[j]): addInterfaceDecl(c, v)
+        addInterfaceDecl(c, v)
-      if isDiscardUnderscore(a.sons[j]):
-        v.flags.incl(sfGenSym)
       when oKeepVariableNames:
         if c.inUnrolledContext > 0: v.flags.incl(sfShadowed)
         else:
@@ -554,7 +553,8 @@ proc semForVars(c: PContext, n: PNode): PNode =
       if getCurrOwner().kind == skModule: incl(v.flags, sfGlobal)
       v.typ = iter.sons[i]
       n.sons[i] = newSymNode(v)
-      if sfGenSym notin v.flags: addForVarDecl(c, v)
+      if sfGenSym notin v.flags and not isDiscardUnderscore(v):
+        addForVarDecl(c, v)
   inc(c.p.nestedLoopCounter)
   n.sons[length-1] = semStmt(c, n.sons[length-1])
   dec(c.p.nestedLoopCounter)

doc/manual/stmts.txt

@@ -129,6 +129,7 @@ initialized and does not rely on syntactic properties:
       x = a()
     use x
 
+
 let statement
 -------------
 
@@ -141,6 +142,19 @@ nor can their address be taken. They cannot be assigned new values.
 For let variables the same pragmas are available as for ordinary variables.
 
 
+Tuple unpacking
+---------------
+
+In a ``var`` or ``let`` statement tuple unpacking can be performed. The special
+identifier ``_`` can be used to ignore some parts of the tuple:
+
+.. code-block:: nim
+    proc returnsTuple(): (int, int, int) = (4, 2, 3)
+
+    let (x, _, z) = returnsTuple()
+
+
+
 Const section
 -------------
 

tests/parser/ttupleunpack.nim

@@ -4,6 +4,11 @@ discard """
   exitcode: 0
 """
 
+proc returnsTuple(): (int, int, int) = (4, 2, 3)
+
+proc main2 =
+  let (x, _, z) = returnsTuple()
+
 proc main() =
 
   proc foo(): tuple[x, y, z: int] =
@@ -16,8 +21,8 @@ proc main() =
   var (a, _, _) = foo()
   doAssert a == 4
 
-  var (a, _, _xx) = foo()
+  var (aa, _, _) = foo()
-  doAssert a == 4
+  doAssert aa == 4
 
   iterator bar(): tuple[x, y, z: int] =
     yield (1,2,3)
@@ -27,3 +32,4 @@ proc main() =
     doAssert y == 2
 
 main()
+main2()