From c52e6c3544450988da6eaffd80e6e61db9b65c6f Mon Sep 17 00:00:00 2001
From: Nick Gasson <nick@nickg.me.uk>
Date: Sat, 30 Dec 2023 11:38:15 +0000
Subject: [PATCH] Allow alias of type attribute

---
 src/sem.c               |  3 +++
 test/sem/attr.vhd       |  1 +
 test/sem/lcs2016_59.vhd | 10 ++++++++++
 test/test_sem.c         | 20 ++++++++++----------
 4 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/src/sem.c b/src/sem.c
index ac30e41e..87806486 100644
--- a/src/sem.c
+++ b/src/sem.c
@@ -1406,6 +1406,8 @@ static bool sem_check_alias(tree_t t, nametab_t *tab)
       else if (tree_kind(decl) == T_VIEW_DECL)
          return true;   // Alias of view declaration
    }
+   else if (value_kind == T_ATTR_REF && is_type_attribute(tree_subkind(value)))
+      return true;   // Alias of type
 
    // Alias of object
    if (!sem_check(value, tab))
@@ -4184,6 +4186,7 @@ static bool sem_check_attr_ref(tree_t t, bool allow_range, nametab_t *tab)
 
    case ATTR_ELEMENT:
    case ATTR_SUBTYPE:
+   case ATTR_INDEX:
       sem_error(t, "%s attribute is only allowed in a type mark", istr(attr));
 
    case ATTR_CONVERSE:
diff --git a/test/sem/attr.vhd b/test/sem/attr.vhd
index 9421f895..414408e6 100644
--- a/test/sem/attr.vhd
+++ b/test/sem/attr.vhd
@@ -216,6 +216,7 @@ begin
         subtype my_int is integer range 1 to 20;
         subtype my_bool is boolean range true to true;
         variable x : integer;
+        alias my_int_base is my_int'base;  -- OK
     begin
         assert my_int'base'left = 1;    -- OK
         assert x'base'left = 2;         -- Error
diff --git a/test/sem/lcs2016_59.vhd b/test/sem/lcs2016_59.vhd
index a7a467a5..6d80fb28 100644
--- a/test/sem/lcs2016_59.vhd
+++ b/test/sem/lcs2016_59.vhd
@@ -233,4 +233,14 @@ begin
 
     end block;
 
+    b4: block is
+        generic (
+            type array_type is array(type is (<>)) of type is private );
+        generic map ( array_type => integer_vector );
+
+        alias index_type   is array_type'INDEX;  -- OK
+        alias element_type is array_type'ELEMENT;  -- OK
+    begin
+    end block;
+
 end architecture;
diff --git a/test/test_sem.c b/test/test_sem.c
index a71f92dc..051525c3 100644
--- a/test/test_sem.c
+++ b/test/test_sem.c
@@ -713,17 +713,17 @@ START_TEST(test_attr)
       { 160, "prefix does not have a range" },
       { 204, "prefix does not have LENGTH attribute" },
       { 212, "cannot use attribute IMAGE with non-scalar type INT2_" },
-      { 221, "prefix of 'BASE attribute must be a type or subtype declara" },
-      { 222, "BASE attribute is allowed only as the prefix of the name" },
-      { 228, "no visible declaration for NOT_HERE" },
-      { 251, "parameter of attribute VAL must have an integer type but "
+      { 222, "prefix of 'BASE attribute must be a type or subtype declara" },
+      { 223, "BASE attribute is allowed only as the prefix of the name" },
+      { 229, "no visible declaration for NOT_HERE" },
+      { 252, "parameter of attribute VAL must have an integer type but "
         "found universal_real" },
-      { 252, "attribute VAL requires a parameter" },
-      { 260, "cannot use attribute VALUE with non-scalar type BIT2D" },
-      { 303, "expression must be a BOOLEAN literal" },
-      { 305, "NEVER_WAITS attribute can only be applied to procedures" },
-      { 309, "failed to parse FOREIGN attribute" },
-      { 310, "FOREIGN attribute must have string literal value" },
+      { 253, "attribute VAL requires a parameter" },
+      { 261, "cannot use attribute VALUE with non-scalar type BIT2D" },
+      { 304, "expression must be a BOOLEAN literal" },
+      { 306, "NEVER_WAITS attribute can only be applied to procedures" },
+      { 310, "failed to parse FOREIGN attribute" },
+      { 311, "FOREIGN attribute must have string literal value" },
       { -1, NULL }
    };
    expect_errors(expect);
-- 
2.39.2