fix(spv-out): OpSourceContinued for large source (gfx-rs#5390)

naga/src/back/spv/helpers.rs

@@ -10,8 +10,12 @@ pub(super) fn bytes_to_words(bytes: &[u8]) -> Vec<Word> {
 
 pub(super) fn string_to_words(input: &str) -> Vec<Word> {
     let bytes = input.as_bytes();
-    let mut words = bytes_to_words(bytes);
 
+    str_bytes_to_words(bytes)
+}
+
+pub(super) fn str_bytes_to_words(bytes: &[u8]) -> Vec<Word> {
+    let mut words = bytes_to_words(bytes);
     if bytes.len() % 4 == 0 {
         // nul-termination
         words.push(0x0u32);
@@ -20,6 +24,21 @@ pub(super) fn string_to_words(input: &str) -> Vec<Word> {
     words
 }
 
+/// split a string into chunks and keep utf8 valid
+#[allow(unstable_name_collisions)]
+pub(super) fn string_to_byte_chunks(input: &str, limit: usize) -> Vec<&[u8]> {
+    let mut offset: usize = 0;
+    let mut start: usize = 0;
+    let mut words = vec![];
+    while offset < input.len() {
+        offset = input.floor_char_boundary(offset + limit);
+        words.push(input[start..offset].as_bytes());
+        start = offset;
+    }
+
+    words
+}
+
 pub(super) const fn map_storage_class(space: crate::AddressSpace) -> spirv::StorageClass {
     match space {
         crate::AddressSpace::Handle => spirv::StorageClass::UniformConstant,
@@ -107,3 +126,35 @@ pub fn global_needs_wrapper(ir_module: &crate::Module, var: &crate::GlobalVariab
         _ => true,
     }
 }
+
+///HACK: this is taken from std unstable, remove it when std's floor_char_boundary is stable
+trait U8Internal {
+    fn is_utf8_char_boundary(&self) -> bool;
+}
+
+impl U8Internal for u8 {
+    fn is_utf8_char_boundary(&self) -> bool {
+        // This is bit magic equivalent to: b < 128 || b >= 192
+        (*self as i8) >= -0x40
+    }
+}
+
+trait StrUnstable {
+    fn floor_char_boundary(&self, index: usize) -> usize;
+}
+
+impl StrUnstable for str {
+    fn floor_char_boundary(&self, index: usize) -> usize {
+        if index >= self.len() {
+            self.len()
+        } else {
+            let lower_bound = index.saturating_sub(3);
+            let new_index = self.as_bytes()[lower_bound..=index]
+                .iter()
+                .rposition(|b| b.is_utf8_char_boundary());
+
+            // SAFETY: we know that the character boundary will be within four bytes
+            unsafe { lower_bound + new_index.unwrap_unchecked() }
+        }
+    }
+}

naga/src/back/spv/instructions.rs

@@ -43,6 +43,42 @@ impl super::Instruction {
         instruction
     }
 
+    pub(super) fn source_continued(source: &[u8]) -> Self {
+        let mut instruction = Self::new(Op::SourceContinued);
+        instruction.add_operands(helpers::str_bytes_to_words(source));
+        instruction
+    }
+
+    pub(super) fn source_auto_continued(
+        source_language: spirv::SourceLanguage,
+        version: u32,
+        source: &Option<DebugInfoInner>,
+    ) -> Vec<Self> {
+        let mut instructions = vec![];
+
+        let with_continue = source.as_ref().and_then(|debug_info| {
+            (debug_info.source_code.len() > u16::MAX as usize).then_some(debug_info)
+        });
+        if let Some(debug_info) = with_continue {
+            let mut instruction = Self::new(Op::Source);
+            instruction.add_operand(source_language as u32);
+            instruction.add_operands(helpers::bytes_to_words(&version.to_le_bytes()));
+
+            let words = helpers::string_to_byte_chunks(debug_info.source_code, u16::MAX as usize);
+            instruction.add_operand(debug_info.source_file_id);
+            instruction.add_operands(helpers::str_bytes_to_words(words[0]));
+            instructions.push(instruction);
+            for word_bytes in words[1..].iter() {
+                let instruction_continue = Self::source_continued(word_bytes);
+                instructions.push(instruction_continue);
+            }
+        } else {
+            let instruction = Self::source(source_language, version, source);
+            instructions.push(instruction);
+        }
+        instructions
+    }
+
     pub(super) fn name(target_id: Word, name: &str) -> Self {
         let mut instruction = Self::new(Op::Name);
         instruction.add_operand(target_id);

naga/src/back/spv/writer.rs

@@ -1899,7 +1899,7 @@ impl Writer {
                     source_code: debug_info.source_code,
                     source_file_id,
                 });
-                self.debugs.push(Instruction::source(
+                self.debugs.append(&mut Instruction::source_auto_continued(
                     spirv::SourceLanguage::Unknown,
                     0,
                     &debug_info_inner,

naga/tests/in/debug-symbol-large-source.param.ron

@@ -0,0 +1,7 @@
+(
+    spv: (
+		version: (1, 1),
+		debug: true,
+		adjust_coordinate_space: false,
+	),
+)