AstGen: disallow leading zeroes in int literals and int types

This makes `0123` and `u0123` etc. illegal.

I'm now confident that this is a good change because
I actually caught two C header translation mistakes in `haiku.zig` with this.
Clearly, `0123` being octal in C (TIL) can cause confusion, and we make this easier to read by
requiring `0o` as the prefix and now also disallowing leading zeroes in integers.

For consistency and because it looks weird, we disallow it for integer types too (e.g. `u0123`).

Fixes #11963
Fixes #12417

1 files changed, 27 insertions, 0 deletions

diff --git a/test/cases/compile_errors/leading_zero_in_integer.zig b/test/cases/compile_errors/leading_zero_in_integer.zig
new file mode 100644
index 0000000000..a818a3d75d
--- /dev/null
+++ b/test/cases/compile_errors/leading_zero_in_integer.zig
@@ -0,0 +1,27 @@
+export fn entry1() void {
+    const T = u000123;
+    _ = T;
+}
+export fn entry2() void {
+    _ = i0;
+    _ = u0;
+    var x: i01 = 1;
+    _ = x;
+}
+export fn entry3() void {
+    _ = 000123;
+}
+export fn entry4() void {
+    _ = 01;
+}
+
+// error
+// backend=llvm
+// target=native
+//
+// :2:15: error: primitive integer type 'u000123' has leading zero
+// :8:12: error: primitive integer type 'i01' has leading zero
+// :12:9: error: integer literal '000123' has leading zero
+// :12:9: note: use '0o' prefix for octal literals
+// :15:9: error: integer literal '01' has leading zero
+// :15:9: note: use '0o' prefix for octal literals