fix elaboration of struct array fields referenced hierarchically

- `expr.name[idx]` considers `expr.name` could be a struct array
- remove fallback struct type lookups which were guaranteed to fail

src/Convert/Struct.hs

@@ -349,7 +349,7 @@ convertSubExpr scopes (Dot e x) =
             else Range e' IndexedMinus (base, len)
 convertSubExpr scopes (Range (Dot e x) NonIndexed rOuter) =
     if isntStruct subExprType then
-        fallbackType scopes orig'
+        (UnknownType, orig')
     else if structIsntReady subExprType then
         (replaceInnerTypeRange NonIndexed rOuter' fieldType, orig')
     else
@@ -371,7 +371,7 @@ convertSubExpr scopes (Range (Dot e x) NonIndexed rOuter) =
             endianCondRange dim rangeLeft rangeRight
 convertSubExpr scopes (Range (Dot e x) mode (baseO, lenO)) =
     if isntStruct subExprType then
-        fallbackType scopes orig'
+        (UnknownType, orig')
     else if structIsntReady subExprType then
         (replaceInnerTypeRange mode (baseO', lenO') fieldType, orig')
     else
@@ -401,7 +401,7 @@ convertSubExpr scopes (Range e mode (left, right)) =
         r' = (left', right')
 convertSubExpr scopes (Bit (Dot e x) i) =
     if isntStruct subExprType then
-        fallbackType scopes orig'
+        (dropInnerTypeRange backupType, orig')
     else if structIsntReady subExprType then
         (dropInnerTypeRange fieldType, orig')
     else
@@ -409,6 +409,7 @@ convertSubExpr scopes (Bit (Dot e x) i) =
     where
         (subExprType, e') = convertSubExpr scopes e
         (_, i') = convertSubExpr scopes i
+        (backupType, _) = fallbackType scopes $ Dot e' x
         orig' = Bit (Dot e' x) i'
         (fieldType, bounds, dims) = lookupFieldInfo subExprType x
         [dim] = dims
@@ -417,7 +418,7 @@ convertSubExpr scopes (Bit (Dot e x) i) =
         iFlat = endianCondExpr dim left right
 convertSubExpr scopes (Bit e i) =
     if t == UnknownType
-        then fallbackType scopes $ Bit e' i'
+        then (UnknownType, Bit e' i')
         else (dropInnerTypeRange t, Bit e' i')
     where
         (t, e') = convertSubExpr scopes e

test/basic/struct_hier_bit.sv

@@ -0,0 +1,12 @@
+module top;
+    if (1) begin : blk
+        struct packed {
+            logic x, y;
+        } [1:0] s;
+    end
+    assign blk.s[0].x = 0;
+    assign top.blk.s[0].y = 1;
+    assign top.blk.s[1].x = 1;
+    assign blk.s[1].y = 0;
+    initial #1 $display("%b", blk.s);
+endmodule

test/basic/struct_hier_bit.v

@@ -0,0 +1,7 @@
+module top;
+    if (1) begin : blk
+        wire [3:0] s;
+    end
+    assign blk.s = 4'b1001;
+    initial #1 $display("%b", blk.s);
+endmodule