From f0026e5019bfc6de23e9dcac99d5d14103432ec9 Mon Sep 17 00:00:00 2001
From: pfg <omegariisthebest@gmail.com>
Date: Mon, 8 Jun 2020 17:20:22 -0700
Subject: [PATCH 1/2] support printing codepoints as {c}

---
 lib/std/fmt.zig | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/lib/std/fmt.zig b/lib/std/fmt.zig
index 671f25a94389..a6b8b29137b6 100644
--- a/lib/std/fmt.zig
+++ b/lib/std/fmt.zig
@@ -530,8 +530,10 @@ pub fn formatIntValue(
     } else if (comptime std.mem.eql(u8, fmt, "c")) {
         if (@TypeOf(int_value).bit_count <= 8) {
             return formatAsciiChar(@as(u8, int_value), options, out_stream);
+        } else if (@TypeOf(int_value).bit_count <= 32) {
+            return formatUnicodeCodepoint(@as(u21, int_value), options, out_stream);
         } else {
-            @compileError("Cannot print integer that is larger than 8 bits as a ascii");
+            @compileError("Cannot print character that is larger than 21 bits as unicode codepoint");
         }
     } else if (comptime std.mem.eql(u8, fmt, "b")) {
         radix = 2;
@@ -590,6 +592,19 @@ pub fn formatAsciiChar(
     return out_stream.writeAll(@as(*const [1]u8, &c));
 }
 
+pub fn formatUnicodeCodepoint(
+    c: u21,
+    options: FormatOptions,
+    out_stream: var,
+) !void {
+    var result: [4]u8 = undefined;
+    const len = std.unicode.utf8Encode(c, &result) catch |e| switch (e) {
+        error.CodepointTooLarge => return out_stream.writeAll("<codepoint too large>"),
+        error.Utf8CannotEncodeSurrogateHalf => return out_stream.writeAll("<invalid codepoint>"),
+    };
+    return out_stream.writeAll(result[0..len]);
+}
+
 pub fn formatBuf(
     buf: []const u8,
     options: FormatOptions,
@@ -1197,6 +1212,10 @@ test "int.specifier" {
         const value: u8 = 'a';
         try testFmt("u8: a\n", "u8: {c}\n", .{value});
     }
+    {
+        const value: u21 = 'あ';
+        try testFmt("u8: あ\n", "u8: {c}\n", .{value});
+    }
     {
         const value: u8 = 0b1100;
         try testFmt("u8: 0b1100\n", "u8: 0b{b}\n", .{value});

From 175d5bf638be7a2fe895c7e491b791933d566ef6 Mon Sep 17 00:00:00 2001
From: pfg <omegariisthebest@gmail.com>
Date: Mon, 8 Jun 2020 17:24:46 -0700
Subject: [PATCH 2/2] {c} codepoint error test

---
 lib/std/fmt.zig | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/lib/std/fmt.zig b/lib/std/fmt.zig
index a6b8b29137b6..a68a45bb65ba 100644
--- a/lib/std/fmt.zig
+++ b/lib/std/fmt.zig
@@ -1214,7 +1214,11 @@ test "int.specifier" {
     }
     {
         const value: u21 = 'あ';
-        try testFmt("u8: あ\n", "u8: {c}\n", .{value});
+        try testFmt("codepoint: あ\n", "codepoint: {c}\n", .{value});
+    }
+    {
+        const value: u21 = 2097151;
+        try testFmt("codepoint: <codepoint too large>\n", "codepoint: {c}\n", .{value});
     }
     {
         const value: u8 = 0b1100;