Avoid emitting extra blank lines for JS library items in jsifier.mjs (emscripten-core#28044)

This change is mostly about cleaning up the code in `addFromLibrary`.

Previously, `depsText` in `src/jsifier.mjs` had two issues that caused
extra blank lines in unoptimized JS output:

1. When `addFromLibrary` was called on an already-emitted dependency, it
   returned `undefined`. Using `.filter((x) => x != '')` did not filter
   out `undefined`, causing `.join('\n')` to emit an empty line for each
   already-emitted dependency.
2. Because `deps` is always an array (`??= []`), the `deps ? ... : ''`
   ternary always took the truthy branch and appended `'\n'`, even when
   no dependencies were emitted. This gave every `addFromLibrary` return
   value a leading `'\n'`.

Use a `joinChunks` helper (`chunks.filter(Boolean).join('\n')`) to join
non-empty dependency, doc comment, and content strings without extra
newlines.

Also update `indentify` in `src/parseTools.mjs` to indent the first line
of non-empty strings, which previously only happened because of the
accidental leading `'\n'` on each item.

Author: sbc100

src/jsifier.mjs

@@ -868,10 +868,7 @@ function(${args}) {
       // Add the docs if they exist and if we are actually emitting a declaration.
       // See the TODO about wasmTable above.
       let docs = LibraryManager.library[symbol + '__docs'];
-      let commentText = '';
-      if (contentText != '' && docs) {
-        commentText += docs + '\n';
-      }
+      const commentText = contentText && docs ? docs : '';
 
       if (EMIT_TSD) {
         LibraryManager.libraryDefinitions[mangled] = {
@@ -880,22 +877,20 @@ function(${args}) {
         };
       }
 
-      const depsText = deps
-        ? deps
-            .map(addDependency)
-            .filter((x) => x != '')
-            .join('\n') + '\n'
-        : '';
+      const joinChunks = (chunks) => chunks.filter(Boolean).join('\n');
+
+      const depsText = joinChunks(deps.map(addDependency));
+
       // Defer direct JS value aliases (`var _alias = _target;`) to `libraryAliases`
       // so the target symbol is guaranteed to be defined first. Skip native
       // aliases (which emit no code here) and signature-mismatch aliases (where
       // `isFunction` is set because they are emitted as forwarding wrapper
       // functions rather than immediate value assignments).
       if (aliasTarget && !isNativeAlias && !isFunction) {
-        libraryAliases.push(commentText + contentText);
-        return depsText.trim();
+        libraryAliases.push(joinChunks([commentText, contentText]));
+        return depsText;
       }
-      return depsText + commentText + contentText;
+      return joinChunks([depsText, commentText, contentText]);
     }
 
     const JS = addFromLibrary(symbol, 'root reference (e.g. compiled C/C++ code)');

src/parseTools.mjs

@@ -346,13 +346,13 @@ function splitI64(value) {
 
 export function indentify(text, indent) {
   // Don't try to indentify huge strings - we may run out of memory
-  if (text.length > 1024 * 1024) return text;
+  if (!text || text.length > 1024 * 1024) return text;
 
   indent = ' '.repeat(indent);
 
   // Perform indentation in a smart fashion that does not leak indentation
   // inside multiline strings enclosed in `` characters.
-  let out = '';
+  let out = indent;
   for (let i = 0; i < text.length; ++i) {
     // Output a C++ comment as-is, don't get confused by ` inside a C++ comment.
     if (text[i] == '/' && text[i + 1] == '/') {

test/codesize/test_codesize_minimal_O0.expected.js

@@ -712,42 +712,33 @@ async function createWasm() {
 
 // Begin JS library code
 
-
   class ExitStatus {
       name = 'ExitStatus';
       constructor(status) {
         this.message = `Program terminated with exit(${status})`;
         this.status = status;
       }
     }
-
   /** @type {!Int32Array} */
   var HEAP32;
-
   /** @type {!Int8Array} */
   var HEAP8;
-
   /** @type {!Uint32Array} */
   var HEAPU32;
-
   var callRuntimeCallbacks = (callbacks) => {
       while (callbacks.length > 0) {
         // Pass the module as the first argument.
         callbacks.shift()(Module);
       }
     };
-
   function ptrToString(ptr) {
       assert(typeof ptr === 'number', `ptrToString expects a number, got ${typeof ptr}`);
       // Convert to 32-bit unsigned value
       ptr >>>= 0;
       return '0x' + ptr.toString(16).padStart(8, '0');
     }
-
   var stackRestore = (val) => __emscripten_stack_restore(val);
-
   var stackSave = () => _emscripten_stack_get_current();
-
   var warnOnce = (text) => {
       warnOnce.shown ||= {};
       if (!warnOnce.shown[text]) {
@@ -757,7 +748,6 @@ async function createWasm() {
       }
     };
 
-  
 // End JS library code
 
 // include: postlibrary.js

test/codesize/test_unoptimized_code_size.json

@@ -1,16 +1,16 @@
 {
-  "hello_world.js": 53049,
-  "hello_world.js.gz": 16879,
+  "hello_world.js": 53002,
+  "hello_world.js.gz": 16858,
   "hello_world.wasm": 14279,
   "hello_world.wasm.gz": 7101,
-  "no_asserts.js": 22107,
-  "no_asserts.js.gz": 7869,
+  "no_asserts.js": 22074,
+  "no_asserts.js.gz": 7852,
   "no_asserts.wasm": 11393,
   "no_asserts.wasm.gz": 5646,
-  "strict.js": 50177,
-  "strict.js.gz": 15887,
+  "strict.js": 50132,
+  "strict.js.gz": 15873,
   "strict.wasm": 14279,
   "strict.wasm.gz": 7098,
-  "total": 165284,
-  "total_gz": 60480
+  "total": 165159,
+  "total_gz": 60428
 }