fix lockfile struct padding (#6495)

* integrity padding

* error message for bytes at end of struct

3 files changed, 18 insertions, 3 deletions

diff --git a/src/install/integrity.zig b/src/install/integrity.zig
index fb9a55509..c0b02d4bf 100644
--- a/src/install/integrity.zig
+++ b/src/install/integrity.zig
@@ -3,8 +3,7 @@ const strings = @import("../string_immutable.zig");
 const Crypto = @import("../sha.zig").Hashers;
 
 pub const Integrity = extern struct {
-    // this is zeroed like this to work around a comptime issue.
-    const empty_digest_buf: [Integrity.digest_buf_len]u8 = [_]u8{ 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
+    const empty_digest_buf: [Integrity.digest_buf_len]u8 = [_]u8{0} ** Integrity.digest_buf_len;
 
     tag: Tag = Tag.unknown,
     /// Possibly a [Subresource Integrity](https://developer.mozilla.org/en-US/docs/Web/Security/Subresource_Integrity) value initially
diff --git a/src/install/lockfile.zig b/src/install/lockfile.zig
index 87d19742b..c1904e962 100644
--- a/src/install/lockfile.zig
+++ b/src/install/lockfile.zig
@@ -4120,6 +4120,7 @@ pub const Package = extern struct {
 
         man_dir: String = String{},
         integrity: Integrity = Integrity{},
+        _padding_integrity: [3]u8 = .{0} ** 3,
 
         /// Does the `cpu` arch and `os` match the requirements listed in the package?
         /// This is completely unrelated to "devDependencies", "peerDependencies", "optionalDependencies" etc
diff --git a/src/install/padding_checker.zig b/src/install/padding_checker.zig
index 1d9405a43..52d343b4f 100644
--- a/src/install/padding_checker.zig
+++ b/src/install/padding_checker.zig
@@ -55,7 +55,6 @@ pub fn assertNoUninitializedPadding(comptime T: type) void {
     // if (info.layout != .Extern) {
     //     @compileError("assertNoUninitializedPadding(" ++ @typeName(T) ++ ") expects an extern struct type, got a struct of layout '" ++ @tagName(info.layout) ++ "'");
     // }
-    var i = 0;
     for (info.fields) |field| {
         const fieldInfo = @typeInfo(field.type);
         switch (fieldInfo) {
@@ -69,9 +68,12 @@ pub fn assertNoUninitializedPadding(comptime T: type) void {
             else => {},
         }
     }
+
     if (info_ == .Union) {
         return;
     }
+
+    var i = 0;
     for (info.fields, 0..) |field, j| {
         const offset = @offsetOf(T, field.name);
         if (offset != i) {
@@ -90,4 +92,17 @@ pub fn assertNoUninitializedPadding(comptime T: type) void {
         }
         i = offset + @sizeOf(field.type);
     }
+
+    if (i != @sizeOf(T)) {
+        @compileError(std.fmt.comptimePrint(
+            \\Expected no possibly uninitialized bytes of memory in '{s}', but found a {d} byte gap at the end of the struct. This can be fixed by adding a padding field to the struct like `padding: [{d}]u8 = .{{0}} ** {d},` between these fields. For more information, look at `padding_checker.zig`
+        ,
+            .{
+                @typeName(T),
+                @sizeOf(T) - i,
+                @sizeOf(T) - i,
+                @sizeOf(T) - i,
+            },
+        ));
+    }
 }