Fix ViewString for string to correctly escape characters needing it

lib/list.gi

@@ -345,7 +345,7 @@ local str,ls, i;
  fi;
 
  if IsString( list ) then
- return Concatenation("\"", list, "\"");
+ return VIEW_STRING_FOR_STRING(list);
  fi;
 
  # make strings for objects in l

src/stringobj.c

@@ -57,6 +57,7 @@
 #include "error.h"
 #include "gaputils.h"
 #include "io.h"
+#include "listfunc.h"
 #include "lists.h"
 #include "modules.h"
 #include "opers.h"
@@ -529,8 +530,11 @@ static Obj CopyString(Obj list, Int mut)
 /****************************************************************************
 **
 *F PrintString(<list>) . . . . . . . . . . . . . . . . . . . print a string
+*F FuncVIEW_STRING_FOR_STRING(<list>) . . . . . . view a string as a string
 **
 ** 'PrintString' prints the string with the handle <list>.
+** 'VIEW_STRING_FOR_STRING' returns a string containing what PrintString
+** outputs.
 **
 ** No linebreaks are allowed, if one must be inserted anyhow, it must
 ** be escaped by a backslash '\', which is done in 'Pr'.
@@ -542,14 +546,38 @@ static Obj CopyString(Obj list, Int mut)
 ** characters. The function can be used to print *any* string in a way
 ** which can be read in by GAP afterwards.
 */
-void PrintString(Obj list)
+
+// Type of function given to OutputStringGeneric
+typedef void StringOutputterType(void * data, char * strbuf, UInt len);
+
+// Output using Pr
+void ToPrOutputter(void * data, char * strbuf, UInt len)
+{
+ strbuf[len++] = '\0';
+ Pr("%s", (Int)strbuf, 0L);
+}
+
+// Output to a string
+void ToStringOutputter(void * data, char * buf, UInt lenbuf)
+{
+ Obj str = (Obj)data;
+ UInt lenstr = GET_LEN_STRING(str);
+ UInt newlen = lenstr + lenbuf;
+ GROW_STRING(str, newlen);
+ memcpy(CHARS_STRING(str) + lenstr, buf, lenbuf);
+ CHARS_STRING(str)[newlen] = '\0';
+ SET_LEN_STRING(str, newlen);
+}
+
+void OutputStringGeneric(Obj list, StringOutputterType func, void * data)
 {
  char PrStrBuf[10007]; /* 7 for a \c\123 at the end */
- UInt scanout, n;
+ UInt scanout = 0, n;
  UInt1 c;
  UInt len = GET_LEN_STRING(list);
  UInt off = 0;
- Pr("\"", 0L, 0L);
+ PrStrBuf[scanout++] = '\"';
+ func(data, PrStrBuf, scanout);
  while (off < len) {
  scanout = 0;
  do {
@@ -606,12 +634,32 @@ void PrintString(Obj list)
  PrStrBuf[scanout++] = c;
  }
  } while (off < len && scanout < 10000);
- PrStrBuf[scanout++] = '\0';
- Pr("%s", (Int)PrStrBuf, 0L);
+ func(data, PrStrBuf, scanout);
  }
- Pr("\"", 0L, 0L);
+ scanout = 0;
+ PrStrBuf[scanout++] = '\"';
+ func(data, PrStrBuf, scanout);
+}
+
+void PrintString(Obj list)
+{
+ OutputStringGeneric(list, ToPrOutputter, (void *)0);
 }
 
+Obj FuncVIEW_STRING_FOR_STRING(Obj self, Obj string)
+{
+ if (!IS_STRING(string)) {
+ RequireArgument("VIEW_STRING_FOR_STRING", string, "must be a string");
+ }
+
+ if (!IS_STRING_REP(string)) {
+ string = CopyToStringRep(string);
+ }
+
+ Obj output = NEW_STRING(0);
+ OutputStringGeneric(string, ToStringOutputter, output);
+ return output;
+}
 
 /****************************************************************************
 **
@@ -1905,7 +1953,7 @@ static StructGVarFilt GVarFilts [] = {
 *V GVarFuncs . . . . . . . . . . . . . . . . . . list of functions to export
 */
 static StructGVarFunc GVarFuncs [] = {
-
+ GVAR_FUNC_1ARGS(VIEW_STRING_FOR_STRING, string),
  GVAR_FUNC_1ARGS(IS_STRING_CONV, string),
  GVAR_FUNC_1ARGS(CONV_STRING, string),
  GVAR_FUNC_1ARGS(COPY_TO_STRING_REP, string),

tst/testinstall/strings.tst

@@ -2,7 +2,7 @@
 ##
 ## This file tests output methods (mainly for strings)
 ##
-#@local x
+#@local x, str
 gap> START_TEST("strings.tst");
 
 # FFE
@@ -42,10 +42,28 @@ gap> String(x);
 "abc"
 gap> x:="\0xFF";
 "\377"
+gap> PrintString(x);
+"\377"
+gap> ViewString(x);
+"\"\\377\""
 gap> x:="\0x42\0x23\0x10\0x10\0x10";
 "B#\020\020\020"
+gap> PrintString(x);
+"B#\020\020\020"
+gap> ViewString(x);
+"\"B#\\020\\020\\020\""
 gap> x:="A string with \0xFF Hex stuff \0x42 in it";
 "A string with \377 Hex stuff B in it"
+gap> PrintString(x);
+"A string with \377 Hex stuff B in it"
+gap> ViewString(x);
+"\"A string with \\377 Hex stuff B in it\""
+gap> x := "\n\t\c\\\"'";
+"\n\t\c\\\"'"
+gap> PrintString(x);
+"\n\t\c\\\"'"
+gap> ViewString(x);
+"\"\\n\\t\\c\\\\\\\"'\""
 gap> "\0yab";
 Syntax error: Expecting hexadecimal escape, or two more octal digits in stream\
 :1
@@ -174,5 +192,12 @@ gap> x:='\0xFF';
 gap> x:='\0xab';
 '\253'
 
+# Huge strings
+gap> for len in [10,100,1000,10000,100000] do
+> str := List([1..len], x -> 'a');
+> Assert(0, Concatenation("\"",str,"\"") = ViewString(str));
+> Assert(0, Concatenation(str,"\n") = DisplayString(str));
+> od;;
+
 #
 gap> STOP_TEST( "strings.tst", 1);