build.rs: don't build compile-shaders if shaders are unchanged

build/vulkan/hash.rs

@@ -0,0 +1,32 @@
+use {std::fmt::Write, walkdir::WalkDir};
+
+pub const ROOT: &str = "src/gfx_apis/vulkan/shaders";
+pub const HASH: &str = "src/gfx_apis/vulkan/shaders_hash.txt";
+
+fn calculate_hash() -> anyhow::Result<String> {
+    let dir = WalkDir::new(ROOT);
+    let mut files = vec![];
+    for file in dir {
+        let file = file?;
+        if file.file_type().is_file() {
+            files.push(file.path().to_path_buf());
+        }
+    }
+    files.sort();
+    let mut out = String::new();
+    for file in files {
+        let data = std::fs::read(&file)?;
+        writeln!(out, "{} {}", blake3::hash(&data).to_hex(), file.display())?;
+    }
+    Ok(out)
+}
+
+pub fn unchanged() -> bool {
+    let Ok(actual) = std::fs::read_to_string(HASH) else {
+        return false;
+    };
+    let Ok(expected) = calculate_hash() else {
+        return false;
+    };
+    actual == expected
+}