1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
// BEGIN - Embark standard lints v0.4
// do not change or add/remove here, but one can add exceptions after this section
// for more info see: <https://github.com/EmbarkStudios/rust-ecosystem/issues/59>
#![deny(unsafe_code)]
#![warn(
    clippy::all,
    clippy::await_holding_lock,
    clippy::char_lit_as_u8,
    clippy::checked_conversions,
    clippy::dbg_macro,
    clippy::debug_assert_with_mut_call,
    clippy::doc_markdown,
    clippy::empty_enum,
    clippy::enum_glob_use,
    clippy::exit,
    clippy::expl_impl_clone_on_copy,
    clippy::explicit_deref_methods,
    clippy::explicit_into_iter_loop,
    clippy::fallible_impl_from,
    clippy::filter_map_next,
    clippy::float_cmp_const,
    clippy::fn_params_excessive_bools,
    clippy::if_let_mutex,
    clippy::implicit_clone,
    clippy::imprecise_flops,
    clippy::inefficient_to_string,
    clippy::invalid_upcast_comparisons,
    clippy::large_types_passed_by_value,
    clippy::let_unit_value,
    clippy::linkedlist,
    clippy::lossy_float_literal,
    clippy::macro_use_imports,
    clippy::manual_ok_or,
    clippy::map_err_ignore,
    clippy::map_flatten,
    clippy::map_unwrap_or,
    clippy::match_on_vec_items,
    clippy::match_same_arms,
    clippy::match_wildcard_for_single_variants,
    clippy::mem_forget,
    clippy::mismatched_target_os,
    clippy::mut_mut,
    clippy::mutex_integer,
    clippy::needless_borrow,
    clippy::needless_continue,
    clippy::option_option,
    clippy::path_buf_push_overwrite,
    clippy::ptr_as_ptr,
    clippy::ref_option_ref,
    clippy::rest_pat_in_fully_bound_structs,
    clippy::same_functions_in_if_condition,
    clippy::semicolon_if_nothing_returned,
    clippy::string_add_assign,
    clippy::string_add,
    clippy::string_lit_as_bytes,
    clippy::string_to_string,
    clippy::todo,
    clippy::trait_duplication_in_bounds,
    clippy::unimplemented,
    clippy::unnested_or_patterns,
    clippy::unused_self,
    clippy::useless_transmute,
    clippy::verbose_file_reads,
    clippy::zero_sized_map_values,
    future_incompatible,
    nonstandard_style,
    rust_2018_idioms
)]
// END - Embark standard lints v0.4
// crate-specific exceptions:
// #![allow()]
#![doc = include_str!("../README.md")]

mod image;

use proc_macro::TokenStream;
use proc_macro2::{Delimiter, Group, Ident, Span, TokenTree};

use syn::{punctuated::Punctuated, spanned::Spanned, visit_mut::VisitMut, ItemFn, Token};

use quote::{quote, ToTokens};
use std::fmt::Write;

/// A macro for creating SPIR-V `OpTypeImage` types. Always produces a
/// `spirv_std::image::Image<...>` type.
///
/// The grammar for the macro is as follows:
///
/// ```rust,ignore
/// Image!(
///     <dimensionality>,
///     <type=...|format=...>,
///     [sampled[=<true|false>],]
///     [multisampled[=<true|false>],]
///     [arrayed[=<true|false>],]
///     [depth[=<true|false>],]
/// )
/// ```
///
/// `=true` can be omitted as shorthand - e.g. `sampled` is short for `sampled=true`.
///
/// A basic example looks like this:
/// ```rust,ignore
/// #[spirv(vertex)]
/// fn main(#[spirv(descriptor_set = 0, binding = 0)] image: &Image!(2D, type=f32, sampled)) {}
/// ```
///
/// ## Arguments
///
/// - `dimensionality` — Dimensionality of an image.
///    Accepted values: `1D`, `2D`, `3D`, `rect`, `cube`, `subpass`.
/// - `type` — The sampled type of an image, mutually exclusive with `format`,
///    when set the image format is unknown.
///    Accepted values: `f32`, `f64`, `u8`, `u16`, `u32`, `u64`, `i8`, `i16`, `i32`, `i64`.
/// - `format` — The image format of the image, mutually exclusive with `type`.
///    Accepted values: Snake case versions of [`ImageFormat`].
/// - `sampled` — Whether it is known that the image will be used with a sampler.
///    Accepted values: `true` or `false`. Default: `unknown`.
/// - `multisampled` — Whether the image contains multisampled content.
///    Accepted values: `true` or `false`. Default: `false`.
/// - `arrayed` — Whether the image contains arrayed content.
///    Accepted values: `true` or `false`. Default: `false`.
/// - `depth` — Whether it is known that the image is a depth image.
///    Accepted values: `true` or `false`. Default: `unknown`.
///
/// [`ImageFormat`]: spirv_std_types::image_params::ImageFormat
///
/// Keep in mind that `sampled` here is a different concept than the `SampledImage` type:
/// `sampled=true` means that this image requires a sampler to be able to access, while the
/// `SampledImage` type bundles that sampler together with the image into a single type (e.g.
/// `sampler2D` in GLSL, vs. `texture2D`).
#[proc_macro]
// The `Image` is supposed to be used in the type position, which
// uses `PascalCase`.
#[allow(nonstandard_style)]
pub fn Image(item: TokenStream) -> TokenStream {
    let output = syn::parse_macro_input!(item as image::ImageType).into_token_stream();

    output.into()
}

/// Replaces all (nested) occurrences of the `#[spirv(..)]` attribute with
/// `#[cfg_attr(target_arch="spirv", rust_gpu::spirv(..))]`.
#[proc_macro_attribute]
pub fn spirv(attr: TokenStream, item: TokenStream) -> TokenStream {
    let mut tokens: Vec<TokenTree> = Vec::new();

    // prepend with #[rust_gpu::spirv(..)]
    let attr: proc_macro2::TokenStream = attr.into();
    tokens.extend(quote! { #[cfg_attr(target_arch="spirv", rust_gpu::spirv(#attr))] });

    let item: proc_macro2::TokenStream = item.into();
    for tt in item {
        match tt {
            TokenTree::Group(group) if group.delimiter() == Delimiter::Parenthesis => {
                let mut sub_tokens = Vec::new();
                for tt in group.stream() {
                    match tt {
                        TokenTree::Group(group)
                            if group.delimiter() == Delimiter::Bracket
                                && matches!(group.stream().into_iter().next(), Some(TokenTree::Ident(ident)) if ident == "spirv")
                                && matches!(sub_tokens.last(), Some(TokenTree::Punct(p)) if p.as_char() == '#') =>
                        {
                            // group matches [spirv ...]
                            let inner = group.stream(); // group stream doesn't include the brackets
                            sub_tokens.extend(
                                quote! { [cfg_attr(target_arch="spirv", rust_gpu::#inner)] },
                            );
                        }
                        _ => sub_tokens.push(tt),
                    }
                }
                tokens.push(TokenTree::from(Group::new(
                    Delimiter::Parenthesis,
                    sub_tokens.into_iter().collect(),
                )));
            }
            _ => tokens.push(tt),
        }
    }
    tokens
        .into_iter()
        .collect::<proc_macro2::TokenStream>()
        .into()
}

/// Marks a function as runnable only on the GPU, and will panic on
/// CPU platforms.
#[proc_macro_attribute]
pub fn gpu_only(_attr: TokenStream, item: TokenStream) -> TokenStream {
    let syn::ItemFn {
        attrs,
        vis,
        sig,
        block,
    } = syn::parse_macro_input!(item as syn::ItemFn);

    // FIXME(eddyb) this looks like a clippy false positive (`sig` is used below).
    #[allow(clippy::redundant_clone)]
    let fn_name = sig.ident.clone();

    let sig_cpu = syn::Signature {
        abi: None,
        ..sig.clone()
    };

    let output = quote::quote! {
        // Don't warn on unused arguments on the CPU side.
        #[cfg(not(target_arch="spirv"))]
        #[allow(unused_variables)]
        #(#attrs)* #vis #sig_cpu {
            unimplemented!(concat!("`", stringify!(#fn_name), "` is only available on SPIR-V platforms."))
        }

        #[cfg(target_arch="spirv")]
        #(#attrs)* #vis #sig {
            #block
        }
    };

    output.into()
}

/// Accepts a function with an argument named `component`, and outputs the
/// function plus a vectorized version of the function which accepts a vector
/// of `component`. This is mostly useful when you have the same impl body for
/// a scalar and vector versions of the same operation.
#[proc_macro_attribute]
#[doc(hidden)]
pub fn vectorized(_attr: TokenStream, item: TokenStream) -> TokenStream {
    let function = syn::parse_macro_input!(item as syn::ItemFn);
    let vectored_function = match create_vectored_fn(function.clone()) {
        Ok(val) => val,
        Err(err) => return err.to_compile_error().into(),
    };

    let output = quote::quote!(
        #function

        #vectored_function
    );

    output.into()
}

fn create_vectored_fn(
    ItemFn {
        attrs,
        vis,
        mut sig,
        block,
    }: ItemFn,
) -> Result<ItemFn, syn::Error> {
    const COMPONENT_ARG_NAME: &str = "component";
    let trait_bound_name = Ident::new("VECTOR", Span::mixed_site());
    let const_bound_name = Ident::new("LENGTH", Span::mixed_site());

    sig.ident = Ident::new(&format!("{}_vector", sig.ident), Span::mixed_site());
    sig.output = syn::ReturnType::Type(
        Default::default(),
        Box::new(path_from_ident(trait_bound_name.clone())),
    );

    let component_type = sig.inputs.iter_mut().find_map(|x| match x {
        syn::FnArg::Typed(ty) => match &*ty.pat {
            syn::Pat::Ident(pat) if pat.ident == COMPONENT_ARG_NAME => Some(&mut ty.ty),
            _ => None,
        },
        syn::FnArg::Receiver(_) => None,
    });

    if component_type.is_none() {
        return Err(syn::Error::new(
            sig.inputs.span(),
            "#[vectorized] requires an argument named `component`.",
        ));
    }
    let component_type = component_type.unwrap();

    let vector_path = {
        let mut path = syn::Path {
            leading_colon: None,
            segments: Punctuated::new(),
        };

        for segment in &["crate", "vector"] {
            path.segments
                .push(Ident::new(segment, Span::mixed_site()).into());
        }

        path.segments.push(syn::PathSegment {
            ident: Ident::new("Vector", Span::mixed_site()),
            arguments: syn::PathArguments::AngleBracketed(syn::AngleBracketedGenericArguments {
                colon2_token: None,
                lt_token: Default::default(),
                args: {
                    let mut punct = Punctuated::new();

                    punct.push(syn::GenericArgument::Type(*component_type.clone()));
                    punct.push(syn::GenericArgument::Type(path_from_ident(
                        const_bound_name.clone(),
                    )));

                    punct
                },
                gt_token: Default::default(),
            }),
        });

        path
    };

    // Replace the original component type with vector version.
    **component_type = path_from_ident(trait_bound_name.clone());

    let trait_bounds = {
        let mut punct = Punctuated::new();
        punct.push(syn::TypeParamBound::Trait(syn::TraitBound {
            paren_token: None,
            modifier: syn::TraitBoundModifier::None,
            lifetimes: None,
            path: vector_path,
        }));
        punct
    };

    sig.generics
        .params
        .push(syn::GenericParam::Type(syn::TypeParam {
            attrs: Vec::new(),
            ident: trait_bound_name,
            colon_token: Some(Token![:](Span::mixed_site())),
            bounds: trait_bounds,
            eq_token: None,
            default: None,
        }));

    sig.generics
        .params
        .push(syn::GenericParam::Const(syn::ConstParam {
            attrs: Vec::default(),
            const_token: Default::default(),
            ident: const_bound_name,
            colon_token: Default::default(),
            ty: syn::Type::Path(syn::TypePath {
                qself: None,
                path: Ident::new("usize", Span::mixed_site()).into(),
            }),
            eq_token: None,
            default: None,
        }));

    Ok(ItemFn {
        attrs,
        vis,
        sig,
        block,
    })
}

fn path_from_ident(ident: Ident) -> syn::Type {
    syn::Type::Path(syn::TypePath {
        qself: None,
        path: syn::Path::from(ident),
    })
}

/// Print a formatted string with a newline using the debug printf extension.
///
/// Examples:
///
/// ```rust,ignore
/// debug_printfln!("uv: %v2f", uv);
/// debug_printfln!("pos.x: %f, pos.z: %f, int: %i", pos.x, pos.z, int);
/// ```
///
/// See <https://github.com/KhronosGroup/Vulkan-ValidationLayers/blob/main/docs/debug_printf.md#debug-printf-format-string> for formatting rules.
#[proc_macro]
pub fn debug_printf(input: TokenStream) -> TokenStream {
    debug_printf_inner(syn::parse_macro_input!(input as DebugPrintfInput))
}

/// Similar to `debug_printf` but appends a newline to the format string.
#[proc_macro]
pub fn debug_printfln(input: TokenStream) -> TokenStream {
    let mut input = syn::parse_macro_input!(input as DebugPrintfInput);
    input.format_string.push('\n');
    debug_printf_inner(input)
}

struct DebugPrintfInput {
    span: proc_macro2::Span,
    format_string: String,
    variables: Vec<syn::Expr>,
}

impl syn::parse::Parse for DebugPrintfInput {
    fn parse(input: syn::parse::ParseStream<'_>) -> syn::parse::Result<Self> {
        let span = input.span();

        if input.is_empty() {
            return Ok(Self {
                span,
                format_string: Default::default(),
                variables: Default::default(),
            });
        }

        let format_string = input.parse::<syn::LitStr>()?;
        if !input.is_empty() {
            input.parse::<syn::token::Comma>()?;
        }
        let variables =
            syn::punctuated::Punctuated::<syn::Expr, syn::token::Comma>::parse_terminated(input)?;

        Ok(Self {
            span,
            format_string: format_string.value(),
            variables: variables.into_iter().collect(),
        })
    }
}

fn parsing_error(message: &str, span: proc_macro2::Span) -> TokenStream {
    syn::Error::new(span, message).to_compile_error().into()
}

enum FormatType {
    Scalar {
        ty: proc_macro2::TokenStream,
    },
    Vector {
        ty: proc_macro2::TokenStream,
        width: usize,
    },
}

fn debug_printf_inner(input: DebugPrintfInput) -> TokenStream {
    let DebugPrintfInput {
        format_string,
        variables,
        span,
    } = input;

    fn map_specifier_to_type(
        specifier: char,
        chars: &mut std::str::Chars<'_>,
    ) -> Option<proc_macro2::TokenStream> {
        let mut peekable = chars.peekable();

        Some(match specifier {
            'd' | 'i' => quote::quote! { i32 },
            'o' | 'x' | 'X' => quote::quote! { u32 },
            'a' | 'A' | 'e' | 'E' | 'f' | 'F' | 'g' | 'G' => quote::quote! { f32 },
            'u' => {
                if matches!(peekable.peek(), Some('l')) {
                    chars.next();
                    quote::quote! { u64 }
                } else {
                    quote::quote! { u32 }
                }
            }
            'l' => {
                if matches!(peekable.peek(), Some('u' | 'x')) {
                    chars.next();
                    quote::quote! { u64 }
                } else {
                    return None;
                }
            }
            _ => return None,
        })
    }

    let mut chars = format_string.chars();
    let mut format_arguments = Vec::new();

    while let Some(mut ch) = chars.next() {
        if ch == '%' {
            ch = match chars.next() {
                Some('%') => continue,
                None => return parsing_error("Unterminated format specifier", span),
                Some(ch) => ch,
            };

            let mut has_precision = false;

            while ch.is_ascii_digit() {
                ch = match chars.next() {
                    Some(ch) => ch,
                    None => {
                        return parsing_error(
                            "Unterminated format specifier: missing type after precision",
                            span,
                        );
                    }
                };

                has_precision = true;
            }

            if has_precision && ch == '.' {
                ch = match chars.next() {
                    Some(ch) => ch,
                    None => {
                        return parsing_error(
                            "Unterminated format specifier: missing type after decimal point",
                            span,
                        );
                    }
                };

                while ch.is_ascii_digit() {
                    ch = match chars.next() {
                        Some(ch) => ch,
                        None => {
                            return parsing_error(
                                "Unterminated format specifier: missing type after fraction precision",
                                span,
                            );
                        }
                    };
                }
            }

            if ch == 'v' {
                let width = match chars.next() {
                    Some('2') => 2,
                    Some('3') => 3,
                    Some('4') => 4,
                    Some(ch) => {
                        return parsing_error(&format!("Invalid width for vector: {ch}"), span);
                    }
                    None => return parsing_error("Missing vector dimensions specifier", span),
                };

                ch = match chars.next() {
                    Some(ch) => ch,
                    None => return parsing_error("Missing vector type specifier", span),
                };

                let ty = match map_specifier_to_type(ch, &mut chars) {
                    Some(ty) => ty,
                    _ => {
                        return parsing_error(
                            &format!("Unrecognised vector type specifier: '{ch}'"),
                            span,
                        );
                    }
                };

                format_arguments.push(FormatType::Vector { ty, width });
            } else {
                let ty = match map_specifier_to_type(ch, &mut chars) {
                    Some(ty) => ty,
                    _ => {
                        return parsing_error(
                            &format!("Unrecognised format specifier: '{ch}'"),
                            span,
                        );
                    }
                };

                format_arguments.push(FormatType::Scalar { ty });
            }
        }
    }

    if format_arguments.len() != variables.len() {
        return syn::Error::new(
            span,
            format!(
                "{} % arguments were found, but {} variables were given",
                format_arguments.len(),
                variables.len()
            ),
        )
        .to_compile_error()
        .into();
    }

    let mut variable_idents = String::new();
    let mut input_registers = Vec::new();
    let mut op_loads = Vec::new();

    for (i, (variable, format_argument)) in variables.into_iter().zip(format_arguments).enumerate()
    {
        let ident = quote::format_ident!("_{}", i);

        let _ = write!(variable_idents, "%{ident} ");

        let assert_fn = match format_argument {
            FormatType::Scalar { ty } => {
                quote::quote! { spirv_std::debug_printf_assert_is_type::<#ty> }
            }
            FormatType::Vector { ty, width } => {
                quote::quote! { spirv_std::debug_printf_assert_is_vector::<#ty, _, #width> }
            }
        };

        input_registers.push(quote::quote! {
            #ident = in(reg) &#assert_fn(#variable),
        });

        let op_load = format!("%{ident} = OpLoad _ {{{ident}}}");

        op_loads.push(quote::quote! {
            #op_load,
        });
    }

    let input_registers = input_registers
        .into_iter()
        .collect::<proc_macro2::TokenStream>();
    let op_loads = op_loads.into_iter().collect::<proc_macro2::TokenStream>();

    let op_string = format!("%string = OpString {format_string:?}");

    let output = quote::quote! {
        ::core::arch::asm!(
            "%void = OpTypeVoid",
            #op_string,
            "%debug_printf = OpExtInstImport \"NonSemantic.DebugPrintf\"",
            #op_loads
            concat!("%result = OpExtInst %void %debug_printf 1 %string ", #variable_idents),
            #input_registers
        )
    };

    output.into()
}

const SAMPLE_PARAM_COUNT: usize = 4;
const SAMPLE_PARAM_GENERICS: [&str; SAMPLE_PARAM_COUNT] = ["B", "L", "G", "S"];
const SAMPLE_PARAM_TYPES: [&str; SAMPLE_PARAM_COUNT] = ["B", "L", "(G,G)", "S"];
const SAMPLE_PARAM_OPERANDS: [&str; SAMPLE_PARAM_COUNT] = ["Bias", "Lod", "Grad", "Sample"];
const SAMPLE_PARAM_NAMES: [&str; SAMPLE_PARAM_COUNT] = ["bias", "lod", "grad", "sample_index"];
const SAMPLE_PARAM_GRAD_INDEX: usize = 2; // Grad requires some special handling because it uses 2 arguments
const SAMPLE_PARAM_EXPLICIT_LOD_MASK: usize = 0b0110; // which params require the use of ExplicitLod rather than ImplicitLod

fn is_grad(i: usize) -> bool {
    i == SAMPLE_PARAM_GRAD_INDEX
}

struct SampleImplRewriter(usize, syn::Type);

impl SampleImplRewriter {
    pub fn rewrite(mask: usize, f: &syn::ItemImpl) -> syn::ItemImpl {
        let mut new_impl = f.clone();
        let mut ty_str = String::from("SampleParams<");

        // based on the mask, form a `SampleParams` type string and add the generic parameters to the `impl<>` generics
        // example type string: `"SampleParams<SomeTy<B>, NoneTy, NoneTy>"`
        for i in 0..SAMPLE_PARAM_COUNT {
            if mask & (1 << i) != 0 {
                new_impl.generics.params.push(syn::GenericParam::Type(
                    syn::Ident::new(SAMPLE_PARAM_GENERICS[i], Span::call_site()).into(),
                ));
                ty_str.push_str("SomeTy<");
                ty_str.push_str(SAMPLE_PARAM_TYPES[i]);
                ty_str.push('>');
            } else {
                ty_str.push_str("NoneTy");
            }
            ty_str.push(',');
        }
        ty_str.push('>');
        let ty: syn::Type = syn::parse(ty_str.parse().unwrap()).unwrap();

        // use the type to insert it into the generic argument of the trait we're implementing
        // e.g., `ImageWithMethods<Dummy>` becomes `ImageWithMethods<SampleParams<SomeTy<B>, NoneTy, NoneTy>>`
        if let Some(t) = &mut new_impl.trait_ {
            if let syn::PathArguments::AngleBracketed(a) =
                &mut t.1.segments.last_mut().unwrap().arguments
            {
                if let Some(syn::GenericArgument::Type(t)) = a.args.last_mut() {
                    *t = ty.clone();
                }
            }
        }

        // rewrite the implemented functions
        SampleImplRewriter(mask, ty).visit_item_impl_mut(&mut new_impl);
        new_impl
    }

    // generates an operands string for use in the assembly, e.g. "Bias %bias Lod %lod", based on the mask
    #[allow(clippy::needless_range_loop)]
    fn get_operands(&self) -> String {
        let mut op = String::new();
        for i in 0..SAMPLE_PARAM_COUNT {
            if self.0 & (1 << i) != 0 {
                if is_grad(i) {
                    op.push_str("Grad %grad_x %grad_y ");
                } else {
                    op.push_str(SAMPLE_PARAM_OPERANDS[i]);
                    op.push_str(" %");
                    op.push_str(SAMPLE_PARAM_NAMES[i]);
                    op.push(' ');
                }
            }
        }
        op
    }

    // generates list of assembly loads for the data, e.g. "%bias = OpLoad _ {bias}", etc.
    #[allow(clippy::needless_range_loop)]
    fn add_loads(&self, t: &mut Vec<TokenTree>) {
        for i in 0..SAMPLE_PARAM_COUNT {
            if self.0 & (1 << i) != 0 {
                if is_grad(i) {
                    t.push(TokenTree::Literal(proc_macro2::Literal::string(
                        "%grad_x = OpLoad _ {grad_x}",
                    )));
                    t.push(TokenTree::Punct(proc_macro2::Punct::new(
                        ',',
                        proc_macro2::Spacing::Alone,
                    )));
                    t.push(TokenTree::Literal(proc_macro2::Literal::string(
                        "%grad_y = OpLoad _ {grad_y}",
                    )));
                    t.push(TokenTree::Punct(proc_macro2::Punct::new(
                        ',',
                        proc_macro2::Spacing::Alone,
                    )));
                } else {
                    let s = format!("%{0} = OpLoad _ {{{0}}}", SAMPLE_PARAM_NAMES[i]);
                    t.push(TokenTree::Literal(proc_macro2::Literal::string(s.as_str())));
                    t.push(TokenTree::Punct(proc_macro2::Punct::new(
                        ',',
                        proc_macro2::Spacing::Alone,
                    )));
                }
            }
        }
    }

    // generates list of register specifications, e.g. `bias = in(reg) &params.bias.0, ...` as separate tokens
    #[allow(clippy::needless_range_loop)]
    fn add_regs(&self, t: &mut Vec<TokenTree>) {
        for i in 0..SAMPLE_PARAM_COUNT {
            if self.0 & (1 << i) != 0 {
                let s = if is_grad(i) {
                    String::from("grad_x=in(reg) &params.grad.0.0,grad_y=in(reg) &params.grad.0.1,")
                } else {
                    format!("{0} = in(reg) &params.{0}.0,", SAMPLE_PARAM_NAMES[i])
                };
                let ts: proc_macro2::TokenStream = s.parse().unwrap();
                t.extend(ts);
            }
        }
    }
}

impl VisitMut for SampleImplRewriter {
    fn visit_impl_item_method_mut(&mut self, item: &mut syn::ImplItemMethod) {
        // rewrite the last parameter of this method to be of type `SampleParams<...>` we generated earlier
        if let Some(syn::FnArg::Typed(p)) = item.sig.inputs.last_mut() {
            *p.ty.as_mut() = self.1.clone();
        }
        syn::visit_mut::visit_impl_item_method_mut(self, item);
    }

    fn visit_macro_mut(&mut self, m: &mut syn::Macro) {
        if m.path.is_ident("asm") {
            // this is where the asm! block is manipulated
            let t = m.tokens.clone();
            let mut new_t = Vec::new();
            let mut altered = false;

            for tt in t {
                match tt {
                    TokenTree::Literal(l) => {
                        if let Ok(l) = syn::parse::<syn::LitStr>(l.to_token_stream().into()) {
                            // found a string literal
                            let s = l.value();
                            if s.contains("$PARAMS") {
                                altered = true;
                                // add load instructions before the sampling instruction
                                self.add_loads(&mut new_t);
                                // and insert image operands
                                let s = s.replace("$PARAMS", &self.get_operands());
                                let lod_type = if self.0 & SAMPLE_PARAM_EXPLICIT_LOD_MASK != 0 {
                                    "ExplicitLod"
                                } else {
                                    "ImplicitLod "
                                };
                                let s = s.replace("$LOD", lod_type);

                                new_t.push(TokenTree::Literal(proc_macro2::Literal::string(
                                    s.as_str(),
                                )));
                            } else {
                                new_t.push(TokenTree::Literal(l.token()));
                            }
                        } else {
                            new_t.push(TokenTree::Literal(l));
                        }
                    }
                    _ => {
                        new_t.push(tt);
                    }
                }
            }

            if altered {
                // finally, add register specs
                self.add_regs(&mut new_t);
            }

            // replace all tokens within the asm! block with our new list
            m.tokens = new_t.into_iter().collect();
        }
    }
}

/// Generates permutations of an `ImageWithMethods` implementation containing sampling functions
/// that have asm instruction ending with a placeholder `$PARAMS` operand. The last parameter
/// of each function must be named `params`, its type will be rewritten. Relevant generic
/// arguments are added to the impl generics.
/// See `SAMPLE_PARAM_GENERICS` for a list of names you cannot use as generic arguments.
#[proc_macro_attribute]
#[doc(hidden)]
pub fn gen_sample_param_permutations(_attr: TokenStream, item: TokenStream) -> TokenStream {
    let item_impl = syn::parse_macro_input!(item as syn::ItemImpl);
    let mut fns = Vec::new();

    for m in 1..(1 << SAMPLE_PARAM_COUNT) {
        fns.push(SampleImplRewriter::rewrite(m, &item_impl));
    }

    // uncomment to output generated tokenstream to stdout
    //println!("{}", quote! { #(#fns)* }.to_string());
    quote! { #(#fns)* }.into()
}