prevent implicitly increasing pointer alignment

See #37

2 files changed, 50 insertions, 0 deletions

diff --git a/test/cases/align.zig b/test/cases/align.zig
index 1de14b084a..383d0389b5 100644
--- a/test/cases/align.zig
+++ b/test/cases/align.zig
@@ -38,3 +38,18 @@ test "bit field alignment" {
 test "default alignment allows unspecified in type syntax" {
     assert(&u32 == &align @alignOf(u32) u32);
 }
+
+test "implicitly decreasing pointer alignment" {
+    const a: u32 align 4 = 3;
+    const b: u32 align 8 = 4;
+    assert(addUnaligned(&a, &b) == 7);
+}
+
+fn addUnaligned(a: &align 1 const u32, b: &align 1 const u32) -> u32 { *a + *b }
+
+test "implicitly decreasing slice alignment" {
+    const a: u32 align 4 = 3;
+    const b: u32 align 8 = 4;
+    assert(addUnalignedSlice((&a)[0..1], (&b)[0..1]) == 7);
+}
+fn addUnalignedSlice(a: []align 1 const u32, b: []align 1 const u32) -> u32 { a[0] + b[0] }
diff --git a/test/compile_errors.zig b/test/compile_errors.zig
index ac5e06d9f3..03110f98e7 100644
--- a/test/compile_errors.zig
+++ b/test/compile_errors.zig
@@ -1976,4 +1976,39 @@ pub fn addCases(cases: &tests.CompileErrorContext) {
         \\}
     ,
         ".tmp_source.zig:1:1: error: declaration shadows type 'u16'");
+
+    cases.add("implicitly increasing pointer alignment",
+        \\const Foo = packed struct {
+        \\    a: u8,
+        \\    b: u32,
+        \\};
+        \\
+        \\export fn entry() {
+        \\    var foo = Foo { .a = 1, .b = 10 };
+        \\    bar(&foo.b);
+        \\}
+        \\
+        \\fn bar(x: &u32) {
+        \\    *x += 1;
+        \\}
+    ,
+        ".tmp_source.zig:8:13: error: expected type '&u32', found '&align 1 u32'");
+
+    cases.add("implicitly increasing slice alignment",
+        \\const Foo = packed struct {
+        \\    a: u8,
+        \\    b: u32,
+        \\};
+        \\
+        \\export fn entry() {
+        \\    var foo = Foo { .a = 1, .b = 10 };
+        \\    foo.b += 1;
+        \\    bar((&foo.b)[0..1]);
+        \\}
+        \\
+        \\fn bar(x: []u32) {
+        \\    x[0] += 1;
+        \\}
+    ,
+        ".tmp_source.zig:9:17: error: expected type '[]u32', found '[]align 1 u32'");
 }