feat: borrow expr, parser fix, borrow tests, borrow example

bootstrap/parser.nim

@@ -601,12 +601,10 @@ proc parseUnary(p: var Parser): Expr =
   case p.peek()
   of tkBorrow:
     discard p.advance()  # borrow
-    let isMut = p.check(tkMut)
+    discard p.expect(tkAmp, "expected '&' after 'borrow'")
+    var isMut = p.check(tkMut)
     if isMut:
       discard p.advance()  # mut
-    discard p.expect(tkAmp, "expected '&' after 'borrow'")
-    if isMut and p.check(tkMut):
-      discard p.advance()  # redundant mut after &
     let operand = p.parseUnary()  # parse the moved value
     return Expr(kind: ekBorrow, loc: loc, exprBorrowOperand: operand, exprBorrowMutable: isMut)
   of tkBang, tkMinus, tkTilde, tkStar, tkAmp:

examples/borrow.bux

@@ -0,0 +1,33 @@
+// borrow.bux — Test explicit borrow expressions
+
+struct Point {
+	x: int;
+	y: int;
+}
+
+// NOT @[Checked] — borrow keyword available everywhere
+func MovePoint(p: *Point) {
+    let ref: &Point = borrow &p;
+    let x: int = (*ref).x;
+}
+
+// @[Checked] enables borrow protection
+@[Checked]
+func SwapPoints(a: *Point, b: *Point) {
+    let ra: &mut Point = borrow &mut a;
+    let rb: &mut Point = borrow &mut b;
+    let tmp: int = (*ra).x;
+    (*ra).x = (*rb).x;
+    (*rb).x = tmp;
+}
+
+func Main() -> int {
+    var p1: Point;
+    p1.x = 10;
+    p1.y = 20;
+    var p2: Point;
+    p2.x = 30;
+    p2.y = 40;
+    SwapPoints(&p1, &p2);
+    return 0;
+}

tests/borrow_test.nim

@@ -26,7 +26,6 @@ func Main() -> int {
 }
 """)
     check(not res.hasErrors)
-
   test "@[Checked] function rejects write through &T":
     let res = checkSource("""
 @[Checked]
@@ -54,7 +53,6 @@ func Main() -> int {
 }
 """)
     check(not res.hasErrors)
-
   test "&T allows reading":
     let res = checkSource("""
 @[Checked]
@@ -68,7 +66,6 @@ func Main() -> int {
 }
 """)
     check(not res.hasErrors)
-
   test "own T type parses and resolves":
     let res = checkSource("""
 struct Box {
@@ -83,7 +80,6 @@ func Main() -> int {
 }
 """)
     check(not res.hasErrors)
-
   test "@[Checked] rejects double mutable borrow in call":
     let res = checkSource("""
 @[Checked]
@@ -139,7 +135,6 @@ func Main() -> int {
 }
 """)
     check(not res.hasErrors)
-
   test "@[Checked] move in assignment":
     let res = checkSource("""
 struct Box {
@@ -172,3 +167,46 @@ func Main() -> int {
 }
 """)
     check(not res.hasErrors)
+
+  test "borrow &mut expr parses and type-checks":
+    let res = checkSource("""
+struct Point {
+  x: int;
+  y: int;
+}
+func Main() -> int {
+  var p: Point;
+  p.x = 10;
+  let r: &mut Point = borrow &mut p;
+  return 0;
+}
+""")
+    check(not res.hasErrors)
+
+  test "@[Shared] attribute parses without errors":
+    let res = checkSource("""
+@[Shared]
+func SharedFunc() -> int {
+  return 42;
+}
+func Main() -> int {
+  return SharedFunc();
+}
+""")
+    check(not res.hasErrors)
+
+  test "borrow & expr with shared ref":
+    let res = checkSource("""
+struct Point {
+  x: int;
+  y: int;
+}
+func Main() -> int {
+  var p: Point;
+  p.x = 10;
+  let r: &Point = borrow &p;
+  let val: int = (*r).x;
+  return val;
+}
+""")
+    check(not res.hasErrors)