Fix filter_tmpl errors (#7763)

compiler/filter_tmpl.nim

@@ -45,7 +45,6 @@ proc scanPar(p: var TTmplParser, d: int) =
   let hi = p.x.len - 1
   while i <= hi:
     case p.x[i]
-    of '\0': break
     of '(': inc(p.par)
     of ')': dec(p.par)
     of '[': inc(p.bracket)
@@ -64,16 +63,22 @@ const
 
 proc parseLine(p: var TTmplParser) =
   var j = 0
-  while p.x[j] == ' ': inc(j)
+  let hi = p.x.len - 1
+
+  if hi == 0:
+    return
+
+  while j <= hi and p.x[j] == ' ': inc(j)
+
   if p.x[0] == p.nimDirective and p.x[1] == '?':
     newLine(p)
   elif p.x[j] == p.nimDirective:
     newLine(p)
     inc(j)
-    while p.x[j] == ' ': inc(j)
+    while j <= hi and p.x[j] == ' ': inc(j)
     let d = j
     var keyw = ""
-    while p.x[j] in PatternChars:
+    while j <= hi and p.x[j] in PatternChars:
       add(keyw, p.x[j])
       inc(j)
 
@@ -127,10 +132,8 @@ proc parseLine(p: var TTmplParser) =
       llStreamWrite(p.outp, "(\"")
       inc(p.emitPar)
     p.state = psTempl
-    while true:
+    while j <= hi:
       case p.x[j]
-      of '\0':
-        break
       of '\x01'..'\x1F', '\x80'..'\xFF':
         llStreamWrite(p.outp, "\\x")
         llStreamWrite(p.outp, toHex(ord(p.x[j]), 2))
@@ -157,11 +160,8 @@ proc parseLine(p: var TTmplParser) =
             llStreamWrite(p.outp, '(')
             inc(j)
             var curly = 0
-            while true:
+            while j <= hi:
               case p.x[j]
-              of '\0':
-                localError(p.info, errXExpected, "}")
-                break
               of '{':
                 inc(j)
                 inc(curly)
@@ -174,6 +174,9 @@ proc parseLine(p: var TTmplParser) =
               else:
                 llStreamWrite(p.outp, p.x[j])
                 inc(j)
+            if curly > 0:
+              localError(p.info, errXExpected, "}")
+              break
             llStreamWrite(p.outp, ')')
             llStreamWrite(p.outp, p.conc)
             llStreamWrite(p.outp, '\"')
@@ -182,7 +185,7 @@ proc parseLine(p: var TTmplParser) =
             llStreamWrite(p.outp, p.conc)
             llStreamWrite(p.outp, p.toStr)
             llStreamWrite(p.outp, '(')
-            while p.x[j] in PatternChars:
+            while j <= hi and p.x[j] in PatternChars:
               llStreamWrite(p.outp, p.x[j])
               inc(j)
             llStreamWrite(p.outp, ')')