InternPool: remove slice from byte aggregate keys

This deletes a ton of lookups and avoids many UAF bugs.

Closes ziglang#19485

Author: jacobly0

lib/std/zig/Zir.zig

@@ -106,12 +106,8 @@ pub const NullTerminatedString = enum(u32) {
 
 /// Given an index into `string_bytes` returns the null-terminated string found there.
 pub fn nullTerminatedString(code: Zir, index: NullTerminatedString) [:0]const u8 {
-    const start = @intFromEnum(index);
-    var end: u32 = start;
-    while (code.string_bytes[end] != 0) {
-        end += 1;
-    }
-    return code.string_bytes[start..end :0];
+    const slice = code.string_bytes[@intFromEnum(index)..];
+    return slice[0..std.mem.indexOfScalar(u8, slice, 0).? :0];
 }
 
 pub fn refSlice(code: Zir, start: usize, len: usize) []Inst.Ref {

src/Compilation.zig

@@ -3159,7 +3159,7 @@ pub fn addModuleErrorMsg(mod: *Module, eb: *ErrorBundle.Wip, module_err_msg: Mod
         const rt_file_path = try module_reference.src_loc.file_scope.fullPath(gpa);
         defer gpa.free(rt_file_path);
         ref_traces.appendAssumeCapacity(.{
-            .decl_name = try eb.addString(ip.stringToSlice(module_reference.decl)),
+            .decl_name = try eb.addString(module_reference.decl.toSlice(ip)),
             .src_loc = try eb.addSourceLocation(.{
                 .src_path = try eb.addString(rt_file_path),
                 .span_start = span.start,
@@ -4074,8 +4074,7 @@ fn workerCheckEmbedFile(
 fn detectEmbedFileUpdate(comp: *Compilation, embed_file: *Module.EmbedFile) !void {
     const mod = comp.module.?;
     const ip = &mod.intern_pool;
-    const sub_file_path = ip.stringToSlice(embed_file.sub_file_path);
-    var file = try embed_file.owner.root.openFile(sub_file_path, .{});
+    var file = try embed_file.owner.root.openFile(embed_file.sub_file_path.toSlice(ip), .{});
     defer file.close();
 
     const stat = try file.stat();
@@ -4444,7 +4443,7 @@ fn reportRetryableEmbedFileError(
     const ip = &mod.intern_pool;
     const err_msg = try Module.ErrorMsg.create(gpa, src_loc, "unable to load '{}{s}': {s}", .{
         embed_file.owner.root,
-        ip.stringToSlice(embed_file.sub_file_path),
+        embed_file.sub_file_path.toSlice(ip),
         @errorName(err),
     });