regenerate: print good error for missing node_modules directory

related to #7

Author: stapelberg

internal/codemirror/bull-codemirror.ts

@@ -1,7 +1,10 @@
-// in the bull/third_party/codemirror directory:
+// To re-generate the CodeMirror editor JavaScript bundle with the currently
+// used versions, run regenerate.sh.
 //
-// npm install codemirror
-// npm install codemirror/lang-markdown
+// To update to a new CodeMirror version, run:
+//
+// (cd third_party/codemirror && npm install codemirror)
+// (cd third_party/codemirror && npm install codemirror/lang-markdown)
 
 import {EditorView} from "codemirror"
 import {markdown} from "@codemirror/lang-markdown"

regenerate.sh

@@ -1,5 +1,19 @@
 #!/bin/sh
 
+if [ ! -d "third_party/codemirror/node_modules" ]
+then
+    echo "Cannot re-generate CodeMirror JavaScript bundle:" >&2
+    echo "" >&2
+    echo "	No node_modules directory found in third_party/codemirror!" >&2
+    echo "" >&2
+    echo "To install the CodeMirror editor and dependencies into third_party," >&2
+    echo "install the npm JavaScript package manager and run:" >&2
+    echo "" >&2
+    echo "	(cd third_party/codemirror && npm install)" >&2
+    echo "" >&2
+    exit 2
+fi
+
 export NODE_PATH=$PWD/third_party/codemirror/node_modules
 go tool esbuild \
    internal/codemirror/bull-codemirror.ts \