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Fix #10712: std.format rejects valid format string with position befo… #11049

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Merged
thewilsonator merged 1 commit into from
Jul 1, 2026
+22 −8
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Fix #10712: std.format rejects valid format string with position befo… #11049

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24 changes: 16 additions & 8 deletions std/format/spec.d
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Original file line number Diff line number Diff line change
Expand Up @@ -280,6 +280,7 @@ if (is(Unqual!Char == Char))
private void fillUp() scope
{
import std.format : enforceFmt, FormatException;
bool canBePosition = true;

// Reset content
if (__ctfe)
Expand Down Expand Up @@ -368,19 +369,20 @@ if (is(Unqual!Char == Char))
// We practically found the format specifier
trailing = trailing[j + 1 .. $];
return;
case '-': flDash = true; ++i; break;
case '+': flPlus = true; ++i; break;
case '=': flEqual = true; ++i; break;
case '#': flHash = true; ++i; break;
case '0': flZero = true; ++i; break;
case ' ': flSpace = true; ++i; break;
case '-': flDash = true; canBePosition = false; ++i; break;
case '+': flPlus = true; canBePosition = false; ++i; break;
case '=': flEqual = true; canBePosition = false; ++i; break;
case '#': flHash = true; canBePosition = false; ++i; break;
case '0': flZero = true; canBePosition = false; ++i; break;
case ' ': flSpace = true; canBePosition = false; ++i; break;
case '*':
canBePosition = false;
++i;
if (i < trailing.length && isDigit(trailing[i]))
{
// a '*' followed by digits and '$' is a
// positional format
trailing = trailing[1 .. $];
trailing = trailing[i .. $];
width = -parse!(typeof(width))(trailing);
i = 0;
enforceFmt(trailing[i++] == '$',
Expand All @@ -400,12 +402,16 @@ if (is(Unqual!Char == Char))
i = trailing.length - tmp.length;
if (tmp.startsWith('$'))
{
enforceFmt(canBePosition,
text("Incorrect format specifier %", trailing[i .. $]));
// index of the form %n$
indexEnd = indexStart = to!ubyte(widthOrArgIndex);
++i;
}
else if (tmp.startsWith(':'))
{
enforceFmt(canBePosition,
text("Incorrect format specifier %", trailing[i .. $]));
// two indexes of the form %m:n$, or one index of the form %m:$
indexStart = to!ubyte(widthOrArgIndex);
tmp = tmp[1 .. $];
Expand All @@ -424,11 +430,13 @@ if (is(Unqual!Char == Char))
else
{
// width
canBePosition = false;
width = to!int(widthOrArgIndex);
}
break;
case ',':
// Separator (default 3 digits)
canBePosition = false;
++i;
flSeparator = true;

Expand Down Expand Up @@ -459,6 +467,7 @@ if (is(Unqual!Char == Char))
break;
case '.':
// Precision
canBePosition = false;
++i;
if (i < trailing.length && trailing[i] == '*')
{
Expand Down Expand Up @@ -985,4 +994,3 @@ void enforceValidFormatSpec(T, Char)(scope const ref FormatSpec!Char f)
assert(collectExceptionMsg!FormatException(format("%.*,*?d", 5))
== "Missing separator digit width argument");
}

6 changes: 6 additions & 0 deletions std/format/write.d
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Original file line number Diff line number Diff line change
Expand Up @@ -771,6 +771,12 @@ if (isSomeString!(typeof(fmt)))
w.clear();
formattedWrite(w, "%s%s", 23, 45);
assert(w.data == "2345", w.data);

w.clear();
formattedWrite(w, "%2$*1$d %3$s", 7, 23, "abc");
assert(w.data == " 23 abc", w.data);
assert(collectExceptionMsg!FormatException(formattedWrite(w, "%*1$2$d %3$s", 7, 23, "abc"))
== "Incorrect format specifier %$d %3$s");
}

// https://issues.dlang.org/show_bug.cgi?id=3479
Expand Down
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