Start typechecking generics

ui-tests/type/generics/generics_on_primitive.nil

@@ -0,0 +1,3 @@
+function main() = (
+    let a: I32[I32] = 0;
+);

ui-tests/type/generics/generics_on_primitive.stderr

@@ -0,0 +1,4 @@
+error: type I32 does not take generic arguments
+ --> $DIR/generics_on_primitive.nil:2
+2 |     let a: I32[I32] = 0;
+               ^^^

ui-tests/type/generics/structs.nil

@@ -0,0 +1,8 @@
+type A[T] = struct { a: T };
+type B[T, U, V] = struct {
+  b: T,
+  d: V,
+};
+type C = ();
+
+function test(a: A[I32], b: B[I32, Int, I32], c: C) = ;

ui-tests/type/generics/structs.stderr

@@ -0,0 +1,4 @@
+error: `main` function not found
+ --> $DIR/structs.nil:1
+1 | type A[T] = struct { a: T };
+    ^

ui-tests/type/generics/wrong_amount.nil

@@ -0,0 +1,23 @@
+type A[T] = struct { a: T };
+type B[T, U, V] = struct {
+  b: T,
+  d: V,
+};
+type C = ();
+
+function test(
+    a1: A,
+    a2: A[],
+    a3: A[I32],
+    a4: A[I32, I32],
+
+    b1: B,
+    b2: B[],
+    b3: B[Int, Int],
+    b4: B[Int, I32, Int],
+    b5: B[Int, Int, Int, Int],
+
+    c1: C,
+    c2: C[],
+    c3: C[I32],
+) = ;

ui-tests/type/generics/wrong_amount.stderr

@@ -0,0 +1,36 @@
+error: expected 1 generic arguments, found 0
+ --> $DIR/wrong_amount.nil:9
+9 |     a1: A,
+            ^
+error: expected 1 generic arguments, found 0
+ --> $DIR/wrong_amount.nil:10
+10 |     a2: A[],
+             ^
+error: expected 1 generic arguments, found 2
+ --> $DIR/wrong_amount.nil:12
+12 |     a4: A[I32, I32],
+             ^
+error: expected 3 generic arguments, found 0
+ --> $DIR/wrong_amount.nil:14
+14 |     b1: B,
+             ^
+error: expected 3 generic arguments, found 0
+ --> $DIR/wrong_amount.nil:15
+15 |     b2: B[],
+             ^
+error: expected 3 generic arguments, found 2
+ --> $DIR/wrong_amount.nil:16
+16 |     b3: B[Int, Int],
+             ^
+error: expected 3 generic arguments, found 4
+ --> $DIR/wrong_amount.nil:18
+18 |     b5: B[Int, Int, Int, Int],
+             ^
+error: type () does not take generic arguments
+ --> $DIR/wrong_amount.nil:22
+22 |     c3: C[I32],
+             ^
+error: `main` function not found
+ --> $DIR/wrong_amount.nil:1
+1 | type A[T] = struct { a: T };
+    ^