More clever handling of variable becomes pattern. Fixes #1996

src/org/rascalmpl/core/library/lang/rascalcore/check/CollectPattern.rsc

@@ -291,7 +291,13 @@ void collect(current: (Pattern) `<Name name> : <Pattern pattern>`, Collector c){
     } else {
         c.push(patternNames, <uname, getLoc(name)>);
         scope = c.getScope();
-        c.define(uname, formalOrPatternFormal(c), name, defLub([pattern], AType(Solver s) { return getPatternType(pattern, avalue(), scope, s); }));
+        c.define(uname, formalOrPatternFormal(c), name, 
+                 defLub([pattern], AType(Solver s) { 
+                    try{
+                        return s.getType(pattern);
+                    } catch _:
+                        return getPatternType(pattern, avalue(), scope, s); 
+                 }));
     }
     collect(pattern, c);
 }

src/org/rascalmpl/core/library/lang/rascalcore/compile/Examples/Tst4.rsc

@@ -1,17 +1,23 @@
 module lang::rascalcore::compile::Examples::Tst4
 
-import IO;
+//alias T = tuple[int, str];
+void main() {
+  //set[tuple[int, str]] r = {};
 
-data Foo = foo(int x);
-list[Foo] foos = [foo(1), foo(2), foo(3)];
+  // Error
+  // `Initialization of `ts1` should be subtype of `rel[int, str]`, found `rel[value, value]``
+  //set[tuple[int, str]] ts1 = {t | t:<int _, _> <- r};
+
+  set[str] a = {};
+  set[str] b = { x| t: x <- a};
+
+  //// No errors
+  //set[T] ts2 = {t | t <- r};
+  //set[T] ts3 = {t | T t:<_, _> <- r};
+  //set[T] ts4 = {<i, s> | <i, s> <- r};
+  //set[T] ts5 = {t | t:<int _, str _> <- r};
+}
 
-void f() {
-    bool foo() = true;
-    println(foo(x) in foos);
-    //      ^^^ Error: "Expected 0 argument(s), found 1"
-    }
-
-
 //value main() = _f(3);
 
 //data Tree;