fix: invalid UTF-8 JSON due to escaped bytes in string literals

changelog.md

@@ -6,6 +6,7 @@
 * `FIX` Deduplicate documentation bindings for parameters
 * `FIX` Correct `math.type` meta return annotation to use `nil` instead of the string literal `'nil'`
 * `FIX` Fix initial `nameStyle.config` not getting loaded in the appropriate workspace.
+* `FIX` Fix invalid LSP responses in files containing string literals with escaped bytes.
 
 ## 3.18.2
 * `CHG` `duplicate-set-field` diagnostic now supports linked suppression: when any occurrence of a duplicate field is suppressed with `---@diagnostic disable` or `---@diagnostic disable-next-line`, all warnings for that field name will be suppressed

script/utility.lua

@@ -469,7 +469,26 @@ local esc = {
     ['\n'] = '\\\n',
 }
 
+local function escapeInvalidUtf8(str)
+    local result = {}
+    local start = 1
+    while true do
+        local _, invalid = utf8Len(str, start)
+        if not invalid then
+            result[#result+1] = str:sub(start)
+            break
+        end
+        result[#result+1] = str:sub(start, invalid - 1)
+        result[#result+1] = ('\\%03d'):format(stringByte(str, invalid))
+        start = invalid + 1
+    end
+    return tableConcat(result)
+end
+
 function m.viewString(str, quo)
+    if not utf8Len(str) then
+        str = escapeInvalidUtf8(str)
+    end
     if not quo then
         if str:find('[\r\n]') then
             quo = '[['

test/other/init.lua

@@ -1 +1,2 @@
 --require 'other.filewatch'
+require 'other.view-string'

test/other/view-string.lua

@@ -0,0 +1,15 @@
+local util = require 'utility'
+
+local function assertView(value, expected)
+    local literal = util.viewString(value)
+    assert(utf8.len(literal))
+    assert(literal == expected, ('expected %q, got %q'):format(expected, literal))
+end
+
+assertView('plain text', '"plain text"')
+assertView('é中文', '"é中文"')
+assertView('\x80', '"\\128"')
+assertView('\xff', '"\\255"')
+assertView('\xc2A', '"\\194A"')
+assertView('\xe2\x82', '"\\226\\130"')
+assertView('[^%w_\x80-\xff]', '"[^%w_\\128-\\255]"')