Automate JS-to-JS library dependencies using Acorn (#27995)

Replace `addImplicitDeps` and `checkDependencies` in `src/jsifier.mjs`
with `calculateDeps`, which uses `acorn.tokenizer` to automatically
detect references to JS library symbols (`$foo` and `_bar`).

Keep the `__deps` mechanism in place for dependencies that static JS
token scanning cannot detect (such as native Wasm/C symbols, function
callbacks in `__deps`, side-effect-only dependencies, and `__postset`
dependencies).

For system libraries we emit a warning when a `__deps` entry is
redundant with an auto-detected dependency. For user JS libraries we
only show this warning in `-sSTRICT` mode.

Performance cost (median of 15 runs on `test/hello_world.c`):
- `tools/compiler.mjs` (`INCLUDE_FULL_LIBRARY=0`): 178.8 ms -> 185.1 ms
(+6.3 ms, +3.5% slower)
- `tools/compiler.mjs` (`INCLUDE_FULL_LIBRARY=1`): 268.2 ms -> 343.1 ms
(+74.9 ms, +27.9% slower)
- `tools/compiler.mjs --symbols-only`: 181.4 ms -> 254.2 ms (+72.8 ms,
+40.1% slower)
- Full `emcc` link (`hello.o` -> `out.js`, cold JS cache):
  - `INCLUDE_FULL_LIBRARY=0`: 661.7 ms -> 740.8 ms (+79.1 ms, +12.0%)
  - `INCLUDE_FULL_LIBRARY=1`: 758.3 ms -> 906.0 ms (+147.7 ms, +19.5%)
- Full `emcc` link (`hello.o` -> `out.js`, warm JS cache):
  - `INCLUDE_FULL_LIBRARY=0`: 271.8 ms (+0.0 ms, 0% slower)
  - `INCLUDE_FULL_LIBRARY=1`: 282.4 ms (+0.0 ms, 0% slower)

Because I'm landing a few cleanup first (#27999, #28059, #28060) there
are zero codesize changes acossiated with this PR.

Fixes: #19098

Author: sbc100

ChangeLog.md

@@ -32,6 +32,10 @@ See docs/process.md for more on how version tagging works.
 - Restored `--whole-archive` behaviour when linking with `-sSIDE_MODULE=1`
   (fixing a regression from 6.0.0 where static archives were no longer included
   in full), while keeping native archive behaviour for `-shared`. (#28055)
+- JavaScript library dependencies on other JavaScript library symbols are now
+  detected automatically by the compiler, so `__deps` is no longer required for
+  direct JS-to-JS references (`__deps` is still supported for dependencies on
+  compiled C/C++ symbols or indirect dependencies). (#27995)
 
 6.0.13 - 10/19/26
 -----------------

site/source/docs/porting/connecting_cpp_and_javascript/Interacting-with-code.rst

@@ -584,16 +584,15 @@ See the `library_*.js`_ files for other examples.
 
 .. note::
 
-   - JavaScript libraries can declare dependencies (``__deps``), however
-     those are only for other JavaScript libraries. See examples in
-     `/src <https://github.com/emscripten-core/emscripten/tree/main/src>`_
-     with the name format **library_*.js**
-   - You can add dependencies for all your methods using
-     ``autoAddDeps(myLibrary, name)`` where myLibrary is the object with
-     all your methods, and ``name`` is the thing they all depend upon.
-     This is useful when all the implemented methods use a JavaScript
-     singleton containing helper methods. See ``library_webgl.js`` for
-     an example.
+   - Direct dependencies between JavaScript library symbols are detected
+     automatically by the compiler. Explicit dependency declarations
+     (``__deps``) are only needed for compiled C/C++ functions or indirect
+     dependencies that are not referenced directly in the symbol's body (such
+     as ``$method_support`` above). See examples in
+     `/src/lib <https://github.com/emscripten-core/emscripten/tree/main/src/lib>`_.
+   - You can add an explicit dependency to all methods in a library using
+     ``autoAddDeps(myLibrary, name)``, where ``myLibrary`` is the object with
+     all your methods and ``name`` is the symbol they all depend upon.
    - The keys passed into `addToLibrary` generate functions that are prefixed
      by ``_``. In other words ``my_func: function() {},`` becomes
      ``function _my_func() {}``, as all C methods in emscripten have a ``_`` prefix. Keys starting with ``$`` have the ``$``