example-runner-ash: make sure spirv-builder uses a dedicated target dir.

examples/runners/ash/build.rs

@@ -0,0 +1,8 @@
+use std::env;
+
+fn main() {
+    // While OUT_DIR is set for both build.rs and compiling the crate, PROFILE is only set in
+    // build.rs. So, export it to crate compilation as well.
+    let profile = env::var("PROFILE").unwrap();
+    println!("cargo:rustc-env=PROFILE={}", profile);
+}

examples/runners/ash/src/main.rs

@@ -197,6 +197,15 @@ pub fn main() {
 }
 
 pub fn compile_shaders() -> Vec<SpvFile> {
+    // Hack: spirv_builder builds into a custom directory if running under cargo, to not
+    // deadlock, and the default target directory if not. However, packages like `proc-macro2`
+    // have different configurations when being built here vs. when building
+    // rustc_codegen_spirv normally, so we *want* to build into a separate target directory, to
+    // not have to rebuild half the crate graph every time we run. So, pretend we're running
+    // under cargo by setting these environment variables.
+    std::env::set_var("OUT_DIR", env!("OUT_DIR"));
+    std::env::set_var("PROFILE", env!("PROFILE"));
+
     let sky_shader_path =
         SpirvBuilder::new("examples/shaders/sky-shader", "spirv-unknown-vulkan1.1")
             .print_metadata(MetadataPrintout::None)