perf(packages/codegen): remove all printSpaceBeforeIdentifier calls (#27620)

Perf optimization.

#27455 removed the only call to `printSpaceBeforeIdentifier` which isn't a no-op in pretty-printing mode (the only mode that `oxc-codegen` currently supports).

Remove `printSpaceBeforeIdentifier` from builds with a `MINIFY` flag which TSDown sets to `false`. Minifier then removes all the calls.

Produces a 0.5%-1% perf improvement on benchmarks.

Reason for using `MINIFY` flag to render the code a no-op, rather than removing all the calls manually, it's it's useful to have the logic in place, in case we want to support minified output in future. It'd be a pain to restore it all if we do that later.

packages/codegen/src-js/globals.d.ts

@@ -13,6 +13,11 @@ declare const TS: boolean;
 // (see `src/asserts.ts`). Release builds strip them in `tsdown_plugins/remove_asserts.ts`.
 declare const DEBUG: boolean;
 
+// `true` if build produces minified output.
+// Always `false` at present - the printer only produces pretty output. Code which only a minifying printer
+// would need sits behind it, so it costs pretty builds nothing, but is kept ready for a minify mode.
+declare const MINIFY: boolean;
+
 // `true` if is benchmark build.
 // Built with `pnpm run bench`, which sets `BENCHMARKS=true`. Benchmark builds honor the
 // `skipSourcemapGeneration` option, so a benchmark can measure the print pass without the final

packages/codegen/src-js/print/space.ts

@@ -47,6 +47,31 @@ if (DEBUG) {
 export function printSpaceBeforeIdentifier(state: State): void {
   debugAssertLastFresh(state);
 
+  // Pretty output never needs this space, so this function is always a no-op.
+  // Only a minifying printer needs the check.
+  //
+  // `last` is never one of the categories the check looks for:
+  //
+  // - The next thing written after a keyword is always either a space (`return x`, `function f`),
+  //   or punctuation (`return;`, `default:`, `function(`, `function<`).
+  //   A space replaces the keyword's `CAT_IDENT` with `CAT_OTHER` before anything which calls this.
+  //   Punctuation does not start with an identifier character, so is never preceded by a call to this.
+  //
+  // - Everything else which writes one of the relevant categories ends a name, an expression or a type:
+  //   - an identifier, `this` or `true` (`CAT_IDENT`)
+  //   - a number (`CAT_INT_DIGIT`)
+  //   - a regex (`CAT_REGEX_SLASH`)
+  //   Nothing starting with an identifier character is ever written straight after one of those.
+  //   The keywords which can follow them (`in`, `of`, `as`, `from`, `extends` etc)
+  //   are always written with a space before them, so do not call this function.
+  //
+  // Release builds remove the calls entirely. Debug builds keep the assertion above,
+  // to ensure `last` stays fresh at every call site, ready for a minify mode.
+  if (!MINIFY) {
+    debugAssert(state.last > CAT_REGEX_SLASH);
+    return;
+  }
+
   // `last` starts as `CAT_OTHER` (start of output behaves like after whitespace),
   // so no empty-output check is needed.
   // Everything needing a space before an identifier is one of the lowest codes, so this is one compare -

packages/codegen/tsdown.config.ts

@@ -25,9 +25,11 @@ const assertPlugins = DEBUG ? [] : [removeAssertsPlugin];
 
 // Global constants defined at build time. See `src-js/globals.d.ts`.
 // `DEBUG: false` lets the minifier remove the body of `debugAssert` and any other debug-only code.
+// `MINIFY` is always `false` - the printer only produces pretty output at present.
 const definedGlobals = {
   DEBUG: DEBUG ? "true" : "false",
   BENCHMARKS: BENCHMARKS ? "true" : "false",
+  MINIFY: "false",
 };
 
 // Base config.