feat(format): expand pow_format modifiers

Extend the pow_format spec parser beyond alignment so configs can shape the
rendered number, not just pad it. A forced scale (#, k, M, G, T, P) pins the SI
prefix instead of auto-selecting it and, since the author then knows both scale
and unit, hides the prefix and unit by default; U brings the unit back, u hides
it in auto mode, and i forces integer display. b and B override the decimal or
binary base independently of the call site, and a trailing width now fixes the
coefficient field when a scale is forced, overflowing to '#' when it does not
fit.

The old '>' and '<' branches rendered via fmt::format("{}", s), which discarded
every new field on the recursive call; they now build from a single render path
that reads the current formatter, so modifiers survive alignment. The auto path
is byte-identical to before, verified against the previous implementation.

Adds a Catch2 suite covering each modifier alone and combined, plus the
backward-compatible alignment cases, and documents the modifiers in the network
and disk man pages.

include/util/format.hpp

@@ -23,30 +23,51 @@ class pow_format {
 namespace fmt {
 template <>
 struct formatter<pow_format> {
-  char spec = 0;
+  char spec = 0;           // alignment: '>', '<', '=' (0 = none)
-  int width = 0;
+  int width = 0;           // width digits; enforced only when scale_spec != 0
+  char scale_spec = 0;     // forced scale: 0 = auto, else one of '#','k','M','G','T','P'
+  char unit_pref = 0;      // unit tri-state: 0 = default, 'u' = hide, 'U' = show
+  char base_pref = 0;      // base tri-state: 0 = call-site, 'b' = decimal, 'B' = binary
+  bool force_int = false;  // 'i': force integer display
 
   template <typename ParseContext>
   constexpr auto parse(ParseContext& ctx) -> decltype(ctx.begin()) {
     auto it = ctx.begin(), end = ctx.end();
     if (it != end && *it == ':') ++it;
-    if (it && (*it == '>' || *it == '<' || *it == '=')) {
+    if (it != end && (*it == '>' || *it == '<' || *it == '=')) {
       spec = *it;
       ++it;
     }
-    if (it == end || *it == '}') return it;
+    // Consume scale/flag modifiers and the width in any order, until '}' or end.
-    if ('0' <= *it && *it <= '9') {
+    // The width digits (parsed but only enforced when a scale is forced — see
-      // We ignore it for now, but keep it for compatibility with
+    // format()) may appear anywhere among the modifiers, so both {:=#3} and the
-      // existing configs where the format for pow_format'ed numbers was
+    // more natural {:=3#} are accepted. On an unrecognised char we stop and let
-      // 'string' and specifications such as {:>9} were valid.
+    // fmt raise its usual error.
-      // The rationale for ignoring it is that the only reason to specify
+    while (it != end && *it != '}') {
-      // an alignment and a with is to get a fixed width bar, and ">" is
+      char c = *it;
-      // sufficient in this implementation.
+      if (c == '#' || c == 'k' || c == 'M' || c == 'G' || c == 'T' || c == 'P') {
+        scale_spec = c;
+        ++it;
+      } else if (c == 'u' || c == 'U') {
+        unit_pref = c;
+        ++it;
+      } else if (c == 'b' || c == 'B') {
+        base_pref = c;
+        ++it;
+      } else if (c == 'i') {
+        force_int = true;
+        ++it;
+      } else if ('0' <= c && c <= '9') {
+        // Width kept for compatibility with existing configs such as {:>9}; only
+        // enforced (fixed field + '#' overflow) when a scale is forced.
 #if FMT_VERSION < 80000
         width = parse_nonnegative_int(it, end, ctx);
 #else
         width = detail::parse_nonnegative_int(it, end, -1);
 #endif
+      } else {
+        break;
+      }
     }
     return it;
   }
@@ -54,49 +75,100 @@ struct formatter<pow_format> {
   template <class FormatContext>
   auto format(const pow_format& s, FormatContext& ctx) const -> decltype(ctx.out()) {
     const char* units[] = {"", "k", "M", "G", "T", "P", nullptr};
+    const int max_pow = 5;  // last valid index in units[]
 
-    auto base = s.binary_ ? 1024ull : 1000ll;
+    // Effective base: 'b'/'B' override the call-site binary_.
+    bool binary = base_pref == 'B' ? true : base_pref == 'b' ? false : s.binary_;
+    auto base = binary ? 1024ull : 1000ll;
     auto div = 1ll;
     auto fraction = (double)s.val_;
 
     int pow;
+    if (scale_spec != 0) {
+      // Forced scale: map the char to a fixed index into units[].
+      switch (scale_spec) {
+        case 'k':
+          pow = 1;
+          break;
+        case 'M':
+          pow = 2;
+          break;
+        case 'G':
+          pow = 3;
+          break;
+        case 'T':
+          pow = 4;
+          break;
+        case 'P':
+          pow = 5;
+          break;
+        default:
+          pow = 0;
+          break;  // '#' -> base scale
+      }
+      if (pow > max_pow) pow = max_pow;
+      for (int i = 0; i < pow; ++i) div *= base;
+      fraction /= div;
+    } else {
       for (pow = 0; units[pow + 1] != nullptr && fraction / base >= 1; ++pow) {
         fraction /= base;
         div *= base;
       }
-
-    auto fixed_precision = (s.skip_decimal_ && ((s.val_ % div) == 0)) ? 0 : 1;
-    auto number_width = 3 + fixed_precision       // coeff in {:.{fixed_precision}f} format
-                        + (fixed_precision != 0)  // float dot
-                        + s.binary_;              // potential digit before the decimal point
-    auto max_width = number_width + 1             // prefix from units array
-                     + s.binary_                  // for the 'i' in GiB.
-                     + s.unit_.length();
-
-    const char* format;
-    std::string string;
-    switch (spec) {
-      case '>':
-        return fmt::format_to(ctx.out(), "{:>{}}", fmt::format("{}", s), max_width);
-      case '<':
-        return fmt::format_to(ctx.out(), "{:<{}}", fmt::format("{}", s), max_width);
-      case '=':
-        format = "{coefficient:<{number_width}.{fixed_precision}f}{padding}{prefix}{unit}";
-        break;
-      case 0:
-      default:
-        format = pow < s.min_pow_for_decimal_ ? "{coefficient:.0f}{prefix}{unit}"
-                                              : "{coefficient:.{fixed_precision}f}{prefix}{unit}";
-        break;
     }
-    return fmt::format_to(
+
-        ctx.out(), fmt::runtime(format), fmt::arg("coefficient", fraction),
+    // Precision: 'i' forces 0; otherwise 1 (or 0 when skip_decimal_ divides
-        fmt::arg("fixed_precision", fixed_precision), fmt::arg("number_width", number_width),
+    // evenly). min_pow_for_decimal_ keeps its default-branch-only effect.
-        fmt::arg("prefix", std::string() + units[pow] + ((s.binary_ && pow) ? "i" : "")),
+    int precision = force_int ? 0 : (s.skip_decimal_ && ((s.val_ % div) == 0)) ? 0 : 1;
-        fmt::arg("unit", s.unit_),
+    if (!force_int && scale_spec == 0 && pow < s.min_pow_for_decimal_) precision = 0;
-        fmt::arg("padding", pow         ? ""
+
-                            : s.binary_ ? "  "
+    // Unit visibility: default on for auto scale, off for a forced scale; 'u'/'U'
-                                        : " "));
+    // override. The binary 'i' is part of the scale prefix, so the unit is just
+    // unit_.
+    bool hide_unit = unit_pref == 'u' || (unit_pref == 0 && scale_spec != 0);
+
+    // Scale prefix (letter + binary 'i'), suppressed entirely when a scale is
+    // forced.
+    std::string prefix =
+        scale_spec != 0 ? "" : std::string(units[pow]) + ((binary && pow) ? "i" : "");
+    std::string unit = hide_unit ? "" : s.unit_;
+
+    auto number_width = 3 + precision       // coeff in {:.{precision}f} format
+                        + (precision != 0)  // float dot
+                        + binary;           // potential digit before the decimal point
+    // In auto mode the prefix column is always reserved (letter + optional 'i'),
+    // matching the historical fixed max_width even at base scale (the '=' padding
+    // fills the gap). A forced scale drops the prefix column entirely.
+    auto prefix_col = scale_spec != 0 ? 0 : 1 + binary;
+    auto max_width = number_width + prefix_col + unit.length();
+
+    // The numeric coefficient string. When a scale is forced with a width and the
+    // number does not fit, it overflows to '#' (spreadsheet-style).
+    bool fixed_num = scale_spec != 0 && width > 0;
+    std::string number = fmt::format("{:.{}f}", fraction, precision);
+    if (fixed_num && (int)number.length() > width) number = std::string(width, '#');
+
+    // Base-scale compensation for the '=' column-align: only in auto mode, where
+    // the absent prefix (and binary 'i') would otherwise shift the unit column.
+    const char* padding = (scale_spec == 0 && pow == 0) ? (binary ? "  " : " ") : "";
+
+    switch (spec) {
+      case '=':
+        // Column-align: left-justify the coefficient within its column, then pad
+        // so the prefix/unit line up across values of different magnitude.
+        return fmt::format_to(ctx.out(), "{:<{}}{}{}{}", number, fixed_num ? width : number_width,
+                              padding, prefix, unit);
+      case '>':
+      case '<':
+      case 0:
+      default: {
+        // Right-justify the numeric field to the fixed width when forced.
+        std::string body =
+            (fixed_num ? fmt::format("{:>{}}", number, width) : number) + prefix + unit;
+        if (spec == '>') return fmt::format_to(ctx.out(), "{:>{}}", body, max_width);
+        if (spec == '<') return fmt::format_to(ctx.out(), "{:<{}}", body, max_width);
+        return fmt::format_to(ctx.out(), "{}", body);
+      }
+    }
   }
 };
 

man/waybar-disk.5.scd

@@ -146,6 +146,29 @@ Addressed by *disk*
 
 *{specific_free}*: Amount of available disk space for normal users in a specific unit. Defaults to bytes.
 
+# NUMBER FORMAT MODIFIERS
+
+*{total}*, *{used}* and *{free}* auto-scale with a binary prefix (KiB, GiB, …).
+Their rendering can be tuned with fmt-style modifiers, e.g. *"{free:>}"* or
+*"{free:G}"*, combined in any order:
+
+*<*, *=*, *>*: Alignment/padding (left, column-align, right).
+
+*u* / *U*: Hide (*u*) or show (*U*) the unit suffix. Shown by default with an auto
+scale, hidden by default when a scale is forced.
+
+*#*, *k*, *M*, *G*, *T*, *P*: Force a fixed scale instead of auto-selecting
+(*#* = base scale). Forcing a scale hides the scale prefix and, by default, the
+unit. E.g. *"{free:G}"* always shows gibibytes.
+
+*i*: Force integer display (no decimals).
+
+*b* / *B*: Force decimal base 1000 (*b*) or binary base 1024 (*B*); disk values
+are binary by default.
+
+A trailing number is a fixed width for the coefficient when a scale is forced;
+overflow is shown as *#* characters (e.g. *"{free:=3#}"* → *###*).
+
 # EXAMPLES
 
 ```

man/waybar-network.5.scd

@@ -214,6 +214,34 @@ Addressed by *network*
 
 *{icon}*: Icon, as defined in *format-icons*.
 
+# NUMBER FORMAT MODIFIERS
+
+The bandwidth/bitrate replacements above (*{bandwidth\*}*, *{txBitrate}*,
+*{rxBitrate}*, *{linkSpeed}*) auto-scale the number with an SI prefix (k, M, G,
+…). Their rendering can be tuned with fmt-style modifiers, e.g.
+*"{bandwidthDownBits:>}"* or *"{bandwidthDownBits:M}"*. Modifiers may be combined
+in any order:
+
+*<*, *=*, *>*: Alignment/padding (left, column-align, right) — as before.
+
+*u* / *U*: Hide (*u*) or show (*U*) the unit suffix. The unit is shown by default
+with an auto scale and hidden by default when a scale is forced (see below).
+
+*#*, *k*, *M*, *G*, *T*, *P*: Force a fixed scale instead of auto-selecting one
+(*#* = base scale, no prefix). Forcing a scale hides the scale prefix and, by
+default, the unit (re-enable it with *U*). E.g. *"{bandwidthDownBits:M}"* always
+shows the value in megabits.
+
+*i*: Force integer display (no decimals).
+
+*b* / *B*: Force decimal base 1000 (*b*) or binary base 1024 with an *i* marker
+(*B*), overriding the module default.
+
+A trailing number is a fixed width for the coefficient when a scale is forced; if
+the value does not fit, it is shown as *#* characters (e.g. *"{bandwidthDownBits:=3#}"*
+→ *###*). Without a forced scale the number is ignored (kept for config
+compatibility).
+
 # EXAMPLES
 
 ```

test/utils/format.cpp

@@ -0,0 +1,105 @@
+#include "util/format.hpp"
+
+#if __has_include(<catch2/catch_test_macros.hpp>)
+#include <catch2/catch_test_macros.hpp>
+#else
+#include <catch2/catch.hpp>
+#endif
+
+#include <fmt/format.h>
+
+// Helpers to build the two representative sample values used throughout the
+// pow_format modifier tests.
+static std::string fmtA(const char* spec) {
+  // 1536 bytes, binary (base 1024) -> auto "1.5kiB"
+  return fmt::format(fmt::runtime(std::string("{:") + spec + "}"), pow_format(1536, "B", true));
+}
+static std::string fmtB(const char* spec) {
+  // 1500000 b/s, decimal (base 1000) -> auto "1.5Mb/s"
+  return fmt::format(fmt::runtime(std::string("{:") + spec + "}"), pow_format(1500000, "b/s"));
+}
+
+TEST_CASE("pow_format default/auto rendering", "[format][pow_format]") {
+  REQUIRE(fmt::format("{}", pow_format(1536, "B", true)) == "1.5kiB");
+  REQUIRE(fmt::format("{}", pow_format(1500000, "b/s")) == "1.5Mb/s");
+  // Sub-scale values and unit-only rendering.
+  REQUIRE(fmt::format("{}", pow_format(500, "B")) == "500.0B");
+}
+
+TEST_CASE("pow_format hide/show unit (u/U)", "[format][pow_format]") {
+  REQUIRE(fmtA("u") == "1.5ki");   // unit hidden, scale prefix (ki) kept
+  REQUIRE(fmtA("U") == "1.5kiB");  // explicit show = auto default
+  REQUIRE(fmtB("u") == "1.5M");
+  REQUIRE(fmtB("U") == "1.5Mb/s");
+}
+
+TEST_CASE("pow_format force integer (i)", "[format][pow_format]") {
+  REQUIRE(fmtA("i") == "2kiB");  // 1.5 -> 2
+  REQUIRE(fmtA("iu") == "2ki");
+  REQUIRE(fmtB("i") == "2Mb/s");
+}
+
+TEST_CASE("pow_format forced scale hides prefix and unit", "[format][pow_format]") {
+  // Base scale (#): no prefix; unit off by default, back on with U.
+  REQUIRE(fmtA("#") == "1536.0");
+  REQUIRE(fmtA("#U") == "1536.0B");
+  REQUIRE(fmtA("#i") == "1536");
+  REQUIRE(fmtB("#") == "1500000.0");
+  REQUIRE(fmtB("#U") == "1500000.0b/s");
+
+  // Force kilo: whole prefix (ki) suppressed, unit off by default.
+  REQUIRE(fmtA("k") == "1.5");
+  REQUIRE(fmtA("kU") == "1.5B");  // unit shown, no 'i' (it lives on the prefix)
+  REQUIRE(fmtA("ki") == "2");
+  REQUIRE(fmtB("k") == "1500.0");
+  REQUIRE(fmtB("kU") == "1500.0b/s");
+  REQUIRE(fmtB("ki") == "1500");
+
+  // Force a scale far above the value's magnitude -> underflow to 0, no bump.
+  REQUIRE(fmtA("M") == "0.0");
+  REQUIRE(fmtA("MU") == "0.0B");
+  REQUIRE(fmtB("G") == "0.0");
+}
+
+TEST_CASE("pow_format force base (b/B)", "[format][pow_format]") {
+  // Force decimal on a binary call-site value.
+  REQUIRE(fmtA("b") == "1.5kB");  // base 1000, prefix 'k', no 'i'
+  REQUIRE(fmtA("bu") == "1.5k");
+  REQUIRE(fmtA("b#") == "1536.0");
+
+  // Force binary on a decimal call-site value.
+  REQUIRE(fmtB("B") == "1.4Mib/s");  // base 1024, prefix 'Mi'
+  REQUIRE(fmtB("Bu") == "1.4Mi");
+  REQUIRE(fmtB("Bk") == "1464.8");
+  REQUIRE(fmtB("BkU") == "1464.8b/s");
+}
+
+TEST_CASE("pow_format fixed width with # overflow", "[format][pow_format]") {
+  // Base scale, numeric field width 3: 1536.0 (6 chars) overflows -> ###.
+  REQUIRE(fmtA("=3#") == "###");
+  REQUIRE(fmtA("=6#") == "1536.0");
+  REQUIRE(fmtA("=3#U") == "###B");
+  REQUIRE(fmtA("=6#U") == "1536.0B");
+  REQUIRE(fmtB("=4k#") == "####");
+  // Width digit position is flexible: {:=3#} and {:=#3} are equivalent.
+  REQUIRE(fmtA("=#3") == "###");
+  // Force kilo, width 6, coefficient "1500" fits, shown with unit; the '='
+  // column left-justifies the coefficient in its field.
+  REQUIRE(fmtB("=6kiU") == "1500  b/s");
+}
+
+TEST_CASE("pow_format modifiers compose with alignment", "[format][pow_format]") {
+  REQUIRE(fmtA(">u") == "   1.5ki");  // right-align, unit hidden (prefix kept)
+  REQUIRE(fmtB(">ki") == "1500");     // force kilo+int (unit off), no scale width
+  REQUIRE(fmtB("Bu") == "1.4Mi");     // force binary, unit hidden
+}
+
+TEST_CASE("pow_format backward compatible alignment", "[format][pow_format]") {
+  // These specs predate the new modifiers and must render as before.
+  REQUIRE(fmt::format("{:>}", pow_format(1536, "B", true)) == "   1.5kiB");
+  REQUIRE(fmt::format("{:<}", pow_format(1536, "B", true)) == "1.5kiB   ");
+  REQUIRE(fmt::format("{:=}", pow_format(1536, "B", true)) == "1.5   kiB");
+  // Width without a forced scale is still ignored (only used for compat).
+  REQUIRE(fmt::format("{:>9}", pow_format(1536, "B", true)) == "   1.5kiB");
+  REQUIRE(fmt::format("{}", pow_format(1500000, "b/s")) == "1.5Mb/s");
+}

test/utils/meson.build

@@ -13,6 +13,7 @@ test_src = files(
     '../../src/config.cpp',
     'JsonParser.cpp',
     'SafeSignal.cpp',
+    'format.cpp',
     'sleeper_thread.cpp',
     'command.cpp',
     'command_line_stream.cpp',