improve automatic type detection at variable assignment time

less error-prone, and now also supports more complex use cases such as loops and destructuring assignments. This was possible by switching the CoffeeScript compiler to a recent contribution by @edemaine at jashkenas/coffeescript#5395

Author: phil294

server/package.json

@@ -22,6 +22,7 @@
   },
   "homepage": "https://github.com/phil294/coffeesense/tree/master/server",
   "dependencies": {
+    "coffeescript": "github:edemaine/coffeescript#var-assign",
     "jshashes": "^1.0.8",
     "typescript": "^4.3.2",
     "volatile-map": "^1.0.2"
@@ -36,7 +37,6 @@
     "@types/resolve": "1.20.0",
     "@typescript-eslint/eslint-plugin": "^5.9.0",
     "@typescript-eslint/parser": "^5.9.0",
-    "coffeescript": "^2.5.1",
     "core-js": "^3.15.1",
     "eslint": "^8.6.0",
     "fast-glob": "^3.2.5",

server/src/services/transpileService.ts

@@ -130,133 +130,6 @@ function postprocess_js(result: ITranspilationResult) {
   // but they do no harm and should go unnoticed
   result.js = result.js.replaceAll(/𒐛: 𒐛,?/g, '')
 
-  // console.time('var-decl-fix')
-  //////////////////////////////////////
-  ///////// Modify variable declarations to solve various TS compiler errors:
-  // Should not be error but is:
-  // xy = 123   # Error: Variable 'xy' implicitly has type 'any' in some locations where its type cannot be determined.CoffeeSense [TS](7034)
-  // => xy      # Error: Variable 'xy' implicitly has an 'any' type.CoffeeSense [TS](7005)
-  //////// and
-  // Should be error but is not:
-  // a = 1
-  // a = 'one'
-  /////// This is because the cs compiler puts variable declarations to the front:
-  // Translates to:
-  // var a;
-  // a = 1;
-  // a = 'one';
-  /////// and now `a` is of type `number | string` (https://github.com/microsoft/TypeScript/issues/45369). 
-  // Below is a hacky workaround that should fix these issues in most cases. It moves the
-  // declaration part (`var`) down to the variable's first implementation position.
-  // This works only with easy implementations and single-variable array destructuring:
-  /*
-  var a, b, c;
-  a = 1;
-  [b] = 2;
-  ({c} = 3);
-  */
-  // Shall become:
-  /*
-  var c;
-  let a = 1;               // added let
-  let [b] = 2;             // added let
-  ({c} = 3);               // unchanged because of surrounding braces
-  */
-  // similarly, array destructors with more than one variable cannot be changed.
-  // Returns stay untouched (return x = 1) too.
-  const js_lines = result.js.split('\n')
-  const js_line_nos = Array.from(Array(js_lines.length).keys())
-  // Part 1: Determine declaration areas (`   var x, y;`)
-  const js_decl_lines_info = js_line_nos
-    .map(decl_line_no => {
-      const match = js_lines[decl_line_no]!.match(/^(\s*)(var )(.+);$/)
-      if(match) {
-        const var_decl_infos = match[3]!.split(', ').map(var_name => ({
-          var_name,
-          decl_indent: match[1]!.length,
-          decl_line_no,
-        }))
-        return {
-          decl_line_no,
-          var_decl_infos,
-        }
-      }
-      return null
-    })
-    .filter(Boolean)
-  // Part 2: For each `var` decl, find fitting first impl statement
-  // (`x = 1`), if present, and return new line content (`let x = 1`).
-  // Might as well be `var x = 1` but this helps differentiating/debugging
-  const js_impl_line_changes = js_decl_lines_info
-    .map(info => info!.var_decl_infos)
-    .flat()
-    .map(({ var_name, decl_indent, decl_line_no }) => {
-      const js_line_nos_after_decl = js_line_nos.slice(decl_line_no)
-      for(const impl_line_no of js_line_nos_after_decl) {
-        const line = js_lines[impl_line_no]!
-        const impl_whitespace = line.match(/^\s*/)![0]!
-        const impl_indent = impl_whitespace.length
-        if(impl_indent < decl_indent)
-          // Parent block scope. Need to skip this variable then, no impl has been found
-          // before current block got closed. It is important to stop here, as otherwise
-          // it might later match an impl from *another* decl of the same var name
-          return null
-        const var_impl_text = `${var_name} = `
-        if(line.substr(impl_indent, var_impl_text.length) === var_impl_text) {
-          if(impl_indent > decl_indent)
-            // This is a conditional first value assignment and type can not safely be set
-            return null
-          const rest_of_line = line.slice(impl_indent + var_impl_text.length)
-          return {
-            var_name,
-            impl_line_no,
-            decl_line_no,
-            new_line_content: `${impl_whitespace}let ${var_impl_text}${rest_of_line}`,
-            new_let_column: impl_indent,
-          }
-        }
-      }
-      return null
-    }).filter(Boolean)
-  // Part 3: Apply Part 2 changes and update source maps of those lines
-  for(const change of js_impl_line_changes) {
-    js_lines[change!.impl_line_no] = change!.new_line_content
-    const map_columns = result.source_map[change!.impl_line_no]!.columns
-    const map_current_impl_start = map_columns[change!.new_let_column]!
-    // Can be null in cases where the variable is not user-set but e.g. a helper
-    // variable put there by the cs compiler itself and ignored otherwise
-    if(map_current_impl_start != null) {
-      map_columns.splice(
-        change!.new_let_column,
-        0,
-        ..."let ".split('').map((_, i) => ({
-          ...map_current_impl_start,
-          column: map_current_impl_start.column + i
-      })))
-      for(let i = map_current_impl_start.column + "let ".length; i < map_columns.length + "let ".length; i++) {
-        if(map_columns[i])
-          map_columns[i]!.column += "let ".length // or = i
-      }
-    }
-  }
-  // Part 4: Update decl lines (Part 1). Where no impl lines were found (Part 2),
-  // keep them. If all were modified, an empty line will be put.
-  for(const decl_line_info of js_decl_lines_info) {
-    let new_decl_line = decl_line_info!.var_decl_infos
-      .filter(decl_info => ! js_impl_line_changes.some(impl_change =>
-        impl_change!.var_name === decl_info.var_name &&
-          impl_change!.decl_line_no === decl_info.decl_line_no))
-      .map(i => i.var_name)
-      .join(', ')
-    if(new_decl_line)
-      // Those that could not be changed
-      new_decl_line = 'var ' + new_decl_line
-    js_lines[decl_line_info!.decl_line_no] = new_decl_line
-  }
-
-  result.js = js_lines.join('\n')
-  // console.timeEnd('var-decl-fix')
-
   /* Prefer object method shorthand */
   result.js = result.js.replaceAll(/([a-zA-Z0-9_$]+): (async )?function(\*?)\(/g, (_, func_name, asynk, asterisk) =>
     `${asynk || ''}${asterisk}${func_name}          (`