Fail when snapshots are missing in CI

packages/parser/Cargo.toml

@@ -12,6 +12,11 @@ exclude = [
 	"test-files",
 ]
 
+[features]
+never-create-snapshots = [
+	"snapshot/never-create"
+]
+
 [dependencies]
 bitflags = { workspace = true }
 gramatika = { workspace = true }

packages/parser/project.json

@@ -9,6 +9,11 @@
 			"executor": "@wgsl/tools:cargo-snapshot-test",
 			"options": {
 				"package": "wgsl-parser"
+			},
+			"configurations": {
+				"ci": {
+					"features": "never-create-snapshots"
+				}
 			}
 		},
 		"lint": {

tools/snapshot/Cargo.toml

@@ -11,3 +11,6 @@ anyhow = { workspace = true }
 pm2 = { package = "proc-macro2", version = "1.0" }
 quote = "1.0"
 syn = { version = "2.0", features = ["full"] }
+
+[features]
+never-create = []

tools/snapshot/src/lib.rs

@@ -46,10 +46,14 @@ fn snapshot_parse(input: SnapshotParse) -> TokenStream {
 	let module_path_ident = format_ident!("mod_path");
 	let module_path_expr = make_module_path_expr();
 
+	let title_ident = format_ident!("title");
+	let title_expr = make_title_expr(&module_path_ident, &snapshot_index_ident);
+
 	let snapshot_ident = format_ident!("snapshot");
-	let snapshot_header_expr = make_snapshot_header_expr(&module_path_ident, &snapshot_index_ident);
+	let snapshot_header_expr = make_snapshot_header_expr(&title_ident);
 
 	let check_and_update_snapshot = make_snapshot_check_and_update_stmts(
+		&title_ident,
 		&module_path_ident,
 		&snapshot_index_ident,
 		&snapshot_ident,
@@ -107,6 +111,7 @@ fn snapshot_parse(input: SnapshotParse) -> TokenStream {
 				accum
 			});
 
+		let #title_ident = #title_expr;
 		let mut #snapshot_ident = #snapshot_header_expr;
 
 		::std::write!(&mut #snapshot_ident, "\n{result}").unwrap();
@@ -149,10 +154,14 @@ fn snapshot_fmt(args: pm2::TokenStream) -> TokenStream {
 	let module_path_ident = format_ident!("mod_path");
 	let module_path_expr = make_module_path_expr();
 
+	let title_ident = format_ident!("title");
+	let title_expr = make_title_expr(&module_path_ident, &snapshot_index_ident);
+
 	let snapshot_ident = format_ident!("snapshot");
-	let snapshot_header_expr = make_snapshot_header_expr(&module_path_ident, &snapshot_index_ident);
+	let snapshot_header_expr = make_snapshot_header_expr(&title_ident);
 
 	let check_and_update_snapshot = make_snapshot_check_and_update_stmts(
+		&title_ident,
 		&module_path_ident,
 		&snapshot_index_ident,
 		&snapshot_ident,
@@ -165,6 +174,7 @@ fn snapshot_fmt(args: pm2::TokenStream) -> TokenStream {
 		let #snapshot_index_ident = #snapshot_index;
 		let #module_path_ident = #module_path_expr;
 
+		let #title_ident = #title_expr;
 		let mut #snapshot_ident = #snapshot_header_expr;
 
 		::std::write!(&mut #snapshot_ident, "\n{}", ::std::format!(#args)).unwrap();
@@ -200,30 +210,47 @@ fn make_module_path_expr() -> pm2::TokenStream {
 	}
 }
 
-fn make_snapshot_header_expr(
-	module_path: &pm2::Ident,
-	snapshot_index: &pm2::Ident,
-) -> pm2::TokenStream {
-	quote! {{
-		let title = ::std::format!(
+fn make_title_expr(module_path: &pm2::Ident, snapshot_index: &pm2::Ident) -> pm2::TokenStream {
+	quote! {
+		::std::format!(
 			"{}::{__func_name__} / #{}",
 			#module_path.iter().join("::"),
 			#snapshot_index,
-		);
+		)
+	}
+}
 
+fn make_snapshot_header_expr(title: &pm2::Ident) -> pm2::TokenStream {
+	quote! {
 		::std::format!(
 			"================================================================================\n\
-			{title}\n\
-			================================================================================"
+			{}\n\
+			================================================================================",
+			#title,
 		)
-	}}
+	}
 }
 
 fn make_snapshot_check_and_update_stmts(
+	#[cfg_attr(not(feature = "never-create"), allow(unused))] title: &pm2::Ident,
 	module_path: &pm2::Ident,
 	snapshot_index: &pm2::Ident,
 	snapshot: &pm2::Ident,
 ) -> pm2::TokenStream {
+	#[cfg(feature = "never-create")]
+	let no_existing_snapshot_stmts = quote! {
+		::core::panic!(
+			"No snapshot exists for test case \"{}\"",
+			#title
+		);
+	};
+
+	#[cfg(not(feature = "never-create"))]
+	let no_existing_snapshot_stmts = quote! {
+		::std::fs::create_dir_all(&dirname).unwrap();
+		::std::fs::write(&full_path, &#snapshot).unwrap();
+	};
+
 	quote! {
 		let crate_root = ::core::env!("CARGO_MANIFEST_DIR");
 		let mut dirname = ::std::path::PathBuf::from(crate_root);
@@ -259,8 +286,7 @@ fn make_snapshot_check_and_update_stmts(
 				}
 			}
 		} else {
-			::std::fs::create_dir_all(&dirname).unwrap();
-			::std::fs::write(&full_path, &#snapshot).unwrap();
+			#no_existing_snapshot_stmts
 		}
 	}
 }