Add example in Makefile showing how we could compile a worker-only wrapper

This is slow and somewhat error prone since it results in recompiling the .wasm files, so I am leaving it out for now.
Also including some unused changes to test-worker.js that I added when trying to get that test running again.

Author: Taytay

Makefile

@@ -1,4 +1,4 @@
-# Note: Last tested with version 1.38.15 of Emscripten
+# Note: Last built with version 1.38.30 of Emscripten
 
 # TODO: Emit a file showing which version of emcc and SQLite was used to compile the emitted output.
 # TODO: Make it easier to use a newer version of Sqlite.
@@ -41,13 +41,13 @@ all: optimized debug worker
 .PHONY: debug
 debug: dist/sql-asm-debug.js dist/sql-wasm-debug.js
 
-dist/sql-asm-debug.js: $(BITCODE_FILES) $(OUTPUT_WRAPPER_FILES) out/api.js exported_functions exported_runtime_methods 
+dist/sql-asm-debug.js: $(BITCODE_FILES) $(OUTPUT_WRAPPER_FILES) out/api.js exported_functions exported_runtime_methods
 	$(EMCC) $(EMFLAGS) $(EMFLAGS_DEBUG) -s WASM=0 $(BITCODE_FILES) --pre-js out/api.js -o $@
 	mv $@ out/tmp-raw.js
 	cat src/shell-pre.js out/tmp-raw.js src/shell-post.js > $@
 	rm out/tmp-raw.js
 
-dist/sql-wasm-debug.js: $(BITCODE_FILES) $(OUTPUT_WRAPPER_FILES) out/api.js exported_functions exported_runtime_methods 
+dist/sql-wasm-debug.js: $(BITCODE_FILES) $(OUTPUT_WRAPPER_FILES) out/api.js exported_functions exported_runtime_methods
 	$(EMCC) $(EMFLAGS) $(EMFLAGS_DEBUG) $(EMFLAGS_WASM) $(BITCODE_FILES) --pre-js out/api.js -o $@
 	mv $@ out/tmp-raw.js
 	cat src/shell-pre.js out/tmp-raw.js src/shell-post.js > $@
@@ -94,6 +94,24 @@ dist/worker.sql-wasm.js: dist/sql-wasm.js out/worker.js
 dist/worker.sql-wasm-debug.js: dist/sql-wasm-debug.js out/worker.js
 	cat $^ > $@
 
+# Building it this way gets us a wrapper that _knows_ it's in worker mode, which is nice.
+# However, since we can't tell emcc that we don't need the wasm generated, and just want the wrapper, we have to pay to have the .wasm generated
+# even though we would have already generated it with our sql-wasm.js target above.
+# This would be made easier if this is implemented: https://github.com/emscripten-core/emscripten/issues/8506
+# dist/worker.sql-wasm.js: $(BITCODE_FILES) $(OUTPUT_WRAPPER_FILES) out/api.js out/worker.js exported_functions exported_runtime_methods dist/sql-wasm-debug.wasm
+# 	$(EMCC) $(EMFLAGS) $(EMFLAGS_OPTIMIZED) -s ENVIRONMENT=worker -s $(EMFLAGS_WASM) $(BITCODE_FILES) --pre-js out/api.js -o out/sql-wasm.js
+# 	mv out/sql-wasm.js out/tmp-raw.js
+# 	cat src/shell-pre.js out/tmp-raw.js src/shell-post.js out/worker.js > $@
+# 	#mv out/sql-wasm.wasm dist/sql-wasm.wasm
+# 	rm out/tmp-raw.js
+
+# dist/worker.sql-wasm-debug.js: $(BITCODE_FILES) $(OUTPUT_WRAPPER_FILES) out/api.js out/worker.js exported_functions exported_runtime_methods dist/sql-wasm-debug.wasm
+# 	$(EMCC) -s ENVIRONMENT=worker $(EMFLAGS) $(EMFLAGS_DEBUG) -s ENVIRONMENT=worker -s WASM_BINARY_FILE=sql-wasm-foo.debug $(EMFLAGS_WASM) $(BITCODE_FILES) --pre-js out/api.js -o out/sql-wasm-debug.js
+# 	mv out/sql-wasm-debug.js out/tmp-raw.js
+# 	cat src/shell-pre.js out/tmp-raw.js src/shell-post.js out/worker.js > $@
+# 	#mv out/sql-wasm-debug.wasm dist/sql-wasm-debug.wasm
+# 	rm out/tmp-raw.js
+
 out/api.js: src/output-pre.js src/api.coffee src/exports.coffee src/api-data.coffee src/output-post.js
 	cat src/api.coffee src/exports.coffee src/api-data.coffee | coffee --bare --compile --stdio > $@
 	cat src/output-pre.js $@ src/output-post.js > out/api-wrapped.js

src/worker.coffee

@@ -1,3 +1,5 @@
+# Since this is only included in web worker builds, I'm not sure if we need to detect this.
+# In fact, it seems like we might want to throw an error if importScripts isn't available.
 if typeof importScripts is 'function' # Detect webworker context
     db = null
 

test/test_worker.js

@@ -2,15 +2,16 @@
 // TODO: Instead of using tiny-worker, we could use the new Node 11 workers via
 // node --experimental-worker test/all.js 
 // Then we could do this:
-// const { Worker } = require('worker_threads');
+//const { Worker } = require('worker_threads');
 // But it turns out that the worker_threads interface is just different enough not to work. 
 var Worker = require("tiny-worker");
 var path = require("path");
 
-
 exports.test = function(notUsed, assert, done) {
 
-  console.error("Skipping: This test is 'expected' to fail because of the way emscripten detects ENVIRONMENT_IS_WORKER.");
+  // We keep running into issues trying to simulate the worker environment.
+  // We really need headless testing of some sort
+  console.error("Skipping: This test is 'expected' to fail because tiny-worker and workerjs don't simulate the environment well enough");
   done();
   return;
 
@@ -26,9 +27,10 @@ exports.test = function(notUsed, assert, done) {
   //
 
   var target = process.argv[2];
-  var file = target ? "sql-"+target : "sql";
+  var file = target ? "sql-"+target : "sql-wasm";
   // If we use tiny-worker, we need to pass in this new cwd as the root of the file being loaded:
-  var worker = new Worker(path.join(__dirname, "../dist/worker."+file+".js"), null, { cwd: path.join(__dirname, "../dist/") });
+  const filename = "../dist/worker."+file+".js";
+  var worker = new Worker(path.join(__dirname, filename), null, { cwd: path.join(__dirname, "../dist/") });
 
   // The following tests are continually overwriting worker.onmessage so that they 
 
@@ -105,17 +107,12 @@ if (!Array.from) {
 }
 
 if (module == require.main) {
-	const target_file = process.argv[2];
-  const sql_loader = require('./load_sql_lib');
-  sql_loader(target_file).then((sql)=>{
-    require('test').run({
-      'test worker': function(assert, done){
-        exports.test(sql, assert, done);
-      }
-    });
-  })
-  .catch((e)=>{
-    console.error(e);
-    assert.fail(e);
+  process.on('unhandledRejection', r => console.log(r));
+
+  require('test').run({
+    'test worker': function(assert, done){
+      exports.test(null, assert, done);
+    }
   });
+
 }