From 3c981f57e2bd10b862f4549bc4b7e81681db3ee4 Mon Sep 17 00:00:00 2001
From: Antonis Geralis <43617260+planetis-m@users.noreply.github.com>
Date: Mon, 9 Feb 2026 17:28:35 +0200
Subject: [PATCH 1/3] Add addSpan procedure for string parsing

---
 lib/pure/parsejson.nim | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/lib/pure/parsejson.nim b/lib/pure/parsejson.nim
index 9292a859641b7..69b3775fe12e3 100644
--- a/lib/pure/parsejson.nim
+++ b/lib/pure/parsejson.nim
@@ -175,23 +175,34 @@ proc parseEscapedUTF16*(buf: cstring, pos: var int): int =
     else:
       return -1
 
+proc addSpan(dst: var string; src: string; startPos, endPos: int) {.inline.} =
+  let n = endPos - startPos
+  if n <= 0:
+    return
+  let oldLen = dst.len
+  setLen(dst, oldLen + n)
+  copyMem(addr dst[oldLen], addr src[startPos], n)
+
 proc parseString(my: var JsonParser): TokKind =
   result = tkString
   var pos = my.bufpos + 1
+  var spanStart = pos
   if my.rawStringLiterals:
     add(my.a, '"')
   while true:
     case my.buf[pos]
     of '\0':
-      my.err = errQuoteExpected
+      addSpan(my.a, my.buf, spanStart, pos)
       result = tkError
       break
     of '"':
+      addSpan(my.a, my.buf, spanStart, pos)
       if my.rawStringLiterals:
         add(my.a, '"')
       inc(pos)
       break
     of '\\':
+      addSpan(my.a, my.buf, spanStart, pos)
       if my.rawStringLiterals:
         add(my.a, '\\')
       case my.buf[pos+1]
@@ -223,19 +234,16 @@ proc parseString(my: var JsonParser): TokKind =
         var pos2 = pos
         var r = parseEscapedUTF16(cstring(my.buf), pos)
         if r < 0:
-          my.err = errInvalidToken
           break
         # Deal with surrogates
         if (r and 0xfc00) == 0xd800:
           if my.buf[pos] != '\\' or my.buf[pos+1] != 'u':
-            my.err = errInvalidToken
             break
           inc(pos, 2)
           var s = parseEscapedUTF16(cstring(my.buf), pos)
           if (s and 0xfc00) == 0xdc00 and s > 0:
             r = 0x10000 + (((r - 0xd800) shl 10) or (s - 0xdc00))
           else:
-            my.err = errInvalidToken
             break
         if my.rawStringLiterals:
           let length = pos - pos2
@@ -251,14 +259,18 @@ proc parseString(my: var JsonParser): TokKind =
         # don't bother with the error
         add(my.a, my.buf[pos])
         inc(pos)
+      spanStart = pos
     of '\c':
+      addSpan(my.a, my.buf, spanStart, pos)
       pos = lexbase.handleCR(my, pos)
       add(my.a, '\c')
+      spanStart = pos
     of '\L':
+      addSpan(my.a, my.buf, spanStart, pos)
       pos = lexbase.handleLF(my, pos)
       add(my.a, '\L')
+      spanStart = pos
     else:
-      add(my.a, my.buf[pos])
       inc(pos)
   my.bufpos = pos # store back
 

From aed70cc752f468dbdc62902e050e090c12779bd7 Mon Sep 17 00:00:00 2001
From: Antonis Geralis <43617260+planetis-m@users.noreply.github.com>
Date: Mon, 9 Feb 2026 22:02:45 +0200
Subject: [PATCH 2/3] Fix CI for addSpan with nimvm, nimscript and js special
 handling

---
 lib/pure/parsejson.nim | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/pure/parsejson.nim b/lib/pure/parsejson.nim
index 69b3775fe12e3..a8dcc04c62191 100644
--- a/lib/pure/parsejson.nim
+++ b/lib/pure/parsejson.nim
@@ -179,9 +179,22 @@ proc addSpan(dst: var string; src: string; startPos, endPos: int) {.inline.} =
   let n = endPos - startPos
   if n <= 0:
     return
-  let oldLen = dst.len
-  setLen(dst, oldLen + n)
-  copyMem(addr dst[oldLen], addr src[startPos], n)
+
+  let old = dst.len
+  dst.setLen old + n
+
+  template impl =
+    for i in 0..<n:
+      dst[old + i] = src[startPos + i]
+
+  when nimvm:
+    impl
+  else:
+    when defined(js) or defined(nimscript):
+      impl
+    else:
+      {.noSideEffect.}:
+        copyMem dst[old].addr, src[startPos].unsafeAddr, n
 
 proc parseString(my: var JsonParser): TokKind =
   result = tkString

From 381a4178b432e52cd865b505918f0d4f9d51618f Mon Sep 17 00:00:00 2001
From: Antonis Geralis <43617260+planetis-m@users.noreply.github.com>
Date: Fri, 27 Feb 2026 19:31:21 +0200
Subject: [PATCH 3/3] Improve error handling in parsejson

Handle invalid token errors for JSON parsing.
---
 lib/pure/parsejson.nim | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/lib/pure/parsejson.nim b/lib/pure/parsejson.nim
index a8dcc04c62191..657f8cc697f50 100644
--- a/lib/pure/parsejson.nim
+++ b/lib/pure/parsejson.nim
@@ -205,6 +205,7 @@ proc parseString(my: var JsonParser): TokKind =
   while true:
     case my.buf[pos]
     of '\0':
+      my.err = errInvalidToken
       addSpan(my.a, my.buf, spanStart, pos)
       result = tkError
       break
@@ -247,16 +248,19 @@ proc parseString(my: var JsonParser): TokKind =
         var pos2 = pos
         var r = parseEscapedUTF16(cstring(my.buf), pos)
         if r < 0:
+          my.err = errInvalidToken
           break
         # Deal with surrogates
         if (r and 0xfc00) == 0xd800:
           if my.buf[pos] != '\\' or my.buf[pos+1] != 'u':
+            my.err = errInvalidToken
             break
           inc(pos, 2)
           var s = parseEscapedUTF16(cstring(my.buf), pos)
           if (s and 0xfc00) == 0xdc00 and s > 0:
             r = 0x10000 + (((r - 0xd800) shl 10) or (s - 0xdc00))
           else:
+            my.err = errInvalidToken
             break
         if my.rawStringLiterals:
           let length = pos - pos2