Add a 'pure' variant of cstyle_format which is infallible

If we cannot fail to output, it doesn't make sense to propagate errors. So if you're SURE there are no errors, use pure_cstyle_format().
If, however, output can fail, use cstyle_format().

This has a drawback of adding quite a bit of code duplication to Format.cpp.
Some of it is dealt using templates, but some code still remains duplicate.

kernel/src/Log.cpp

@@ -26,14 +26,8 @@ static void log_serial(LogLevel level, const char* format, va_list origin)
 
     Serial::printf("%4zu.%.3zu ", Timer::ticks(), Timer::ticks_ms() - (Timer::ticks() * 1000));
 
-    cstyle_format(
-        format,
-        [](char c, void*) -> Result<void> {
-            Serial::putchar((u8)c);
-            return {};
-        },
-        nullptr, ap)
-        .expect_value("Sanity check failed in log_serial: Should never fail");
+    pure_cstyle_format(
+        format, [](char c, void*) { Serial::putchar((u8)c); }, nullptr, ap);
 
     Serial::putchar('\n');
 
@@ -56,14 +50,8 @@ static void log_text_console(LogLevel level, const char* format, va_list origin)
     else
         TextConsole::set_foreground(WHITE);
 
-    cstyle_format(
-        format,
-        [](char c, void*) -> Result<void> {
-            TextConsole::putchar(c);
-            return {};
-        },
-        nullptr, ap)
-        .expect_value("Sanity check failed in log_text_console: Should never fail");
+    pure_cstyle_format(
+        format, [](char c, void*) { TextConsole::putchar(c); }, nullptr, ap);
 
     TextConsole::putchar('\n');
 

kernel/src/arch/Serial.cpp

@@ -25,14 +25,8 @@ namespace Serial
     {
         va_list ap;
         va_start(ap, format);
-        auto rc = cstyle_format(
-                      format,
-                      [](char c, void*) -> Result<void> {
-                          putchar((u8)c);
-                          return {};
-                      },
-                      nullptr, ap)
-                      .expect_value("Sanity check failed in Serial::printf: Should never fail");
+        auto rc = pure_cstyle_format(
+            format, [](char c, void*) { putchar((u8)c); }, nullptr, ap);
         va_end(ap);
         return rc;
     }

kernel/src/video/TextConsole.cpp

@@ -161,14 +161,8 @@ namespace TextConsole
     {
         va_list ap;
         va_start(ap, format);
-        auto rc = cstyle_format(
-                      format,
-                      [](char c, void*) -> Result<void> {
-                          putchar(c);
-                          return {};
-                      },
-                      nullptr, ap)
-                      .expect_value("Sanity check failed in TextConsole::printf: Should never fail");
+        auto rc = pure_cstyle_format(
+            format, [](char c, void*) { putchar(c); }, nullptr, ap);
         va_end(ap);
         return rc;
     }

luna/include/luna/Format.h

@@ -4,7 +4,9 @@
 #include <stdarg.h>
 
 typedef Result<void> (*callback_t)(char, void*);
+typedef void (*pure_callback_t)(char, void*);
 
 Result<usize> cstyle_format(const char* format, callback_t callback, void* arg, va_list ap);
+usize pure_cstyle_format(const char* format, pure_callback_t callback, void* arg, va_list ap);
 usize vstring_format(char* buf, usize max, const char* format, va_list ap);
 usize string_format(char* buf, usize max, const char* format, ...);

luna/src/Format.cpp

@@ -26,6 +26,13 @@ struct format_state
     void* arg;
 };
 
+struct pure_format_state
+{
+    usize count;
+    pure_callback_t callback;
+    void* arg;
+};
+
 struct conv_state
 {
     flags_t flags;
@@ -39,6 +46,12 @@ static Result<void> format_putchar(char c, format_state& state)
     return state.callback(c, state.arg);
 }
 
+static void pure_format_putchar(char c, pure_format_state& state)
+{
+    state.count++;
+    return state.callback(c, state.arg);
+}
+
 static Result<void> format_puts(const char* s, format_state& state)
 {
     while (*s)
@@ -50,6 +63,15 @@ static Result<void> format_puts(const char* s, format_state& state)
     return {};
 }
 
+static void pure_format_puts(const char* s, pure_format_state& state)
+{
+    while (*s)
+    {
+        pure_format_putchar(*s, state);
+        s++;
+    }
+}
+
 static Result<void> start_pad(const conv_state& vstate, format_state& state, usize start)
 {
     if (!(vstate.flags & FLAG_LEFT_ALIGN))
@@ -60,6 +82,14 @@ static Result<void> start_pad(const conv_state& vstate, format_state& state, usi
     return {};
 }
 
+static void pure_start_pad(const conv_state& vstate, pure_format_state& state, usize start)
+{
+    if (!(vstate.flags & FLAG_LEFT_ALIGN))
+    {
+        while (start++ < vstate.width) pure_format_putchar(' ', state);
+    }
+}
+
 static Result<void> end_pad(const conv_state& vstate, format_state& state, usize start)
 {
     if (vstate.flags & FLAG_LEFT_ALIGN)
@@ -70,6 +100,14 @@ static Result<void> end_pad(const conv_state& vstate, format_state& state, usize
     return {};
 }
 
+static void pure_end_pad(const conv_state& vstate, pure_format_state& state, usize start)
+{
+    if (vstate.flags & FLAG_LEFT_ALIGN)
+    {
+        while (start++ < vstate.width) pure_format_putchar(' ', state);
+    }
+}
+
 static flags_t parse_flags(const char** format)
 {
     flags_t result = 0;
@@ -203,7 +241,34 @@ static usize to_string(usize value, usize base, char* buf, usize max, bool upper
     return i;
 }
 
-static Result<void> output_integer(char specifier, conv_state& vstate, format_state& state, usize value, bool negative)
+static Result<void> output_integer_data(conv_state& vstate, format_state& state, char* buf, usize len)
+{
+    if (!(vstate.flags & FLAG_ZERO_PAD)) TRY(start_pad(vstate, state, len));
+
+    usize i = len;
+
+    while (i--) TRY(format_putchar(buf[i], state));
+
+    TRY(end_pad(vstate, state, len));
+
+    return {};
+}
+
+static void output_pure_integer_data(conv_state& vstate, pure_format_state& state, char* buf, usize len)
+{
+    if (!(vstate.flags & FLAG_ZERO_PAD)) pure_start_pad(vstate, state, len);
+
+    usize i = len;
+
+    while (i--) pure_format_putchar(buf[i], state);
+
+    pure_end_pad(vstate, state, len);
+}
+
+template <typename ReturnType, typename FormatStateType>
+static ReturnType output_integer_generic(char specifier, conv_state& vstate, FormatStateType& state, usize value,
+                                         bool negative,
+                                         ReturnType (*output_data)(conv_state&, FormatStateType&, char*, usize))
 {
     usize base = 10;
     bool uppercase = false;
@@ -260,18 +325,27 @@ static Result<void> output_integer(char specifier, conv_state& vstate, format_st
             buf[buflen++] = ' ';
     }
 
-    if (!(vstate.flags & FLAG_ZERO_PAD)) TRY(start_pad(vstate, state, buflen));
-
-    usize i = buflen;
-
-    while (i--) TRY(format_putchar(buf[i], state));
-
-    TRY(end_pad(vstate, state, buflen));
-
-    return {};
+    return output_data(vstate, state, buf, buflen);
 }
 
-static Result<void> va_output_integer(char specifier, conv_state& vstate, format_state& state, va_list ap)
+static Result<void> output_integer(char specifier, conv_state& vstate, format_state& state, usize value, bool negative)
+{
+    return output_integer_generic<Result<void>, format_state>(specifier, vstate, state, value, negative,
+                                                              output_integer_data);
+}
+
+static void pure_output_integer(char specifier, conv_state& vstate, pure_format_state& state, usize value,
+                                bool negative)
+{
+    return output_integer_generic<void, pure_format_state>(specifier, vstate, state, value, negative,
+                                                           output_pure_integer_data);
+}
+
+template <typename ReturnType, typename FormatStateType>
+static ReturnType va_generic_output_integer(char specifier, conv_state& vstate, FormatStateType& state,
+                                            ReturnType (*integer_output)(char, conv_state&, FormatStateType&, usize,
+                                                                         bool),
+                                            va_list ap)
 {
     bool is_signed = false;
     bool negative = false;
@@ -290,12 +364,12 @@ static Result<void> va_output_integer(char specifier, conv_state& vstate, format
                 v = -v;
                 negative = true;
             }
-            return output_integer(specifier, vstate, state, (unsigned char)v, negative);
+            return integer_output(specifier, vstate, state, (unsigned char)v, negative);
         }
         else
         {
             const unsigned char v = (unsigned char)va_arg(ap, unsigned int);
-            return output_integer(specifier, vstate, state, v, false);
+            return integer_output(specifier, vstate, state, v, false);
         }
     }
     else if (vstate.flags & FLAG_SHORT)
@@ -308,12 +382,12 @@ static Result<void> va_output_integer(char specifier, conv_state& vstate, format
                 v = -v;
                 negative = true;
             }
-            return output_integer(specifier, vstate, state, (unsigned short)v, negative);
+            return integer_output(specifier, vstate, state, (unsigned short)v, negative);
         }
         else
         {
             const unsigned short v = (unsigned short)va_arg(ap, unsigned int);
-            return output_integer(specifier, vstate, state, v, false);
+            return integer_output(specifier, vstate, state, v, false);
         }
     }
     else if (vstate.flags & FLAG_LONG_LONG)
@@ -326,12 +400,12 @@ static Result<void> va_output_integer(char specifier, conv_state& vstate, format
                 v = -v;
                 negative = true;
             }
-            return output_integer(specifier, vstate, state, (unsigned long long)v, negative);
+            return integer_output(specifier, vstate, state, (unsigned long long)v, negative);
         }
         else
         {
             const unsigned long long v = va_arg(ap, unsigned long long);
-            return output_integer(specifier, vstate, state, v, false);
+            return integer_output(specifier, vstate, state, v, false);
         }
     }
     else if (vstate.flags & FLAG_LONG)
@@ -344,12 +418,12 @@ static Result<void> va_output_integer(char specifier, conv_state& vstate, format
                 v = -v;
                 negative = true;
             }
-            return output_integer(specifier, vstate, state, (unsigned long)v, negative);
+            return integer_output(specifier, vstate, state, (unsigned long)v, negative);
         }
         else
         {
             const unsigned long v = va_arg(ap, unsigned long);
-            return output_integer(specifier, vstate, state, v, false);
+            return integer_output(specifier, vstate, state, v, false);
         }
     }
     else
@@ -362,16 +436,26 @@ static Result<void> va_output_integer(char specifier, conv_state& vstate, format
                 v = -v;
                 negative = true;
             }
-            return output_integer(specifier, vstate, state, (unsigned int)v, negative);
+            return integer_output(specifier, vstate, state, (unsigned int)v, negative);
         }
         else
         {
             const unsigned int v = va_arg(ap, unsigned int);
-            return output_integer(specifier, vstate, state, v, false);
+            return integer_output(specifier, vstate, state, v, false);
         }
     }
 }
 
+static Result<void> va_output_integer(char specifier, conv_state& vstate, format_state& state, va_list ap)
+{
+    return va_generic_output_integer<Result<void>, format_state>(specifier, vstate, state, output_integer, ap);
+}
+
+static void va_pure_output_integer(char specifier, conv_state& vstate, pure_format_state& state, va_list ap)
+{
+    return va_generic_output_integer<void, pure_format_state>(specifier, vstate, state, pure_output_integer, ap);
+}
+
 Result<usize> cstyle_format(const char* format, callback_t callback, void* arg, va_list ap)
 {
     format_state state;
@@ -472,6 +556,106 @@ Result<usize> cstyle_format(const char* format, callback_t callback, void* arg,
     return state.count;
 }
 
+usize pure_cstyle_format(const char* format, pure_callback_t callback, void* arg, va_list ap)
+{
+    pure_format_state state;
+    state.callback = callback;
+    state.arg = arg;
+    state.count = 0;
+
+    while (*format)
+    {
+        if (*format != '%')
+        {
+            pure_format_putchar(*format, state);
+            format++;
+            continue;
+        }
+
+        format++;
+
+        if (*format == '%')
+        {
+            pure_format_putchar('%', state);
+            continue;
+        }
+
+        // %[flags][width][.precision][length]conversion
+
+        flags_t flags = parse_flags(&format);
+        const usize width = parse_width(&format, flags, ap);
+        usize precision = parse_precision(&format, flags, ap);
+        parse_length(&format, flags);
+
+        conv_state vstate = {flags, width, precision};
+
+        const char specifier = *format;
+        format++;
+
+        if (is_integer_format_specifier(specifier))
+        {
+            va_pure_output_integer(specifier, vstate, state, ap);
+            continue;
+        }
+        else if (specifier == 'p')
+        {
+            const void* ptr = va_arg(ap, void*);
+            if (ptr == nullptr)
+            {
+                pure_start_pad(vstate, state, 5);
+                pure_format_puts("(nil)", state);
+                pure_end_pad(vstate, state, 5);
+                continue;
+            }
+            vstate.width = (sizeof(void*) * 2) + 2;
+            vstate.flags |= (FLAG_ZERO_PAD | FLAG_ALTERNATE);
+            pure_output_integer('p', vstate, state, (usize)ptr, false);
+            continue;
+        }
+        else if (specifier == 'c')
+        {
+            const char c = (char)va_arg(ap, int);
+
+            pure_start_pad(vstate, state, 1);
+            pure_format_putchar(c, state);
+            pure_end_pad(vstate, state, 1);
+
+            continue;
+        }
+        else if (specifier == 's')
+        {
+            const char* str = va_arg(ap, const char*);
+            if (str == nullptr)
+            {
+                pure_start_pad(vstate, state, 6);
+                pure_format_puts("(null)", state);
+                pure_end_pad(vstate, state, 6);
+                continue;
+            }
+            else
+            {
+                usize len = strlen(str);
+
+                bool use_precision = (flags & FLAG_USE_PRECISION);
+                if (use_precision && len > precision) len = precision;
+
+                pure_start_pad(vstate, state, len);
+                while (*str && (!use_precision || precision))
+                {
+                    pure_format_putchar(*str, state);
+                    precision--;
+                    str++;
+                }
+                pure_end_pad(vstate, state, len);
+                continue;
+            }
+        }
+        else { continue; }
+    }
+
+    return state.count;
+}
+
 struct StringFormatInfo
 {
     char* buffer;
@@ -482,18 +666,17 @@ usize vstring_format(char* buf, usize max, const char* format, va_list ap)
 {
     StringFormatInfo info = {.buffer = buf, .remaining = max - 1};
 
-    usize result = cstyle_format(
-                       format,
-                       [](char c, void* arg) -> Result<void> {
-                           StringFormatInfo* info_arg = (StringFormatInfo*)arg;
-                           if (!info_arg->remaining) return {};
-                           *(info_arg->buffer) = c;
-                           info_arg->buffer++;
-                           info_arg->remaining--;
-                           return {};
-                       },
-                       &info, ap)
-                       .expect_value("Sanity check failed in vstring_format: Should never fail");
+    usize result = pure_cstyle_format(
+        format,
+        [](char c, void* arg) {
+            StringFormatInfo* info_arg = (StringFormatInfo*)arg;
+            if (!info_arg->remaining) return;
+            *(info_arg->buffer) = c;
+            info_arg->buffer++;
+            info_arg->remaining--;
+            return;
+        },
+        &info, ap);
 
     *(info.buffer) = 0;