use explicit error sets for utf8Decode functions

and run unicode tests at comptime also

std/unicode.zig

@@ -57,11 +57,12 @@ pub fn utf8Encode(c: u32, out: []u8) !u3 {
     return length;
 }
 
+const Utf8DecodeError = Utf8Decode2Error || Utf8Decode3Error || Utf8Decode4Error;
 /// Decodes the UTF-8 codepoint encoded in the given slice of bytes.
 /// bytes.len must be equal to utf8ByteSequenceLength(bytes[0]) catch unreachable.
 /// If you already know the length at comptime, you can call one of
 /// utf8Decode2,utf8Decode3,utf8Decode4 directly instead of this function.
-pub fn utf8Decode(bytes: []const u8) !u32 {
+pub fn utf8Decode(bytes: []const u8) Utf8DecodeError!u32 {
     return switch (bytes.len) {
         1 => u32(bytes[0]),
         2 => utf8Decode2(bytes),
@@ -71,7 +72,11 @@ pub fn utf8Decode(bytes: []const u8) !u32 {
     };
 }
 
-pub fn utf8Decode2(bytes: []const u8) !u32 {
+const Utf8Decode2Error = error{
+    Utf8ExpectedContinuation,
+    Utf8OverlongEncoding,
+};
+pub fn utf8Decode2(bytes: []const u8) Utf8Decode2Error!u32 {
     debug.assert(bytes.len == 2);
     debug.assert(bytes[0] & 0b11100000 == 0b11000000);
     var value: u32 = bytes[0] & 0b00011111;
@@ -85,7 +90,12 @@ pub fn utf8Decode2(bytes: []const u8) !u32 {
     return value;
 }
 
-pub fn utf8Decode3(bytes: []const u8) !u32 {
+const Utf8Decode3Error = error{
+    Utf8ExpectedContinuation,
+    Utf8OverlongEncoding,
+    Utf8EncodesSurrogateHalf,
+};
+pub fn utf8Decode3(bytes: []const u8) Utf8Decode3Error!u32 {
     debug.assert(bytes.len == 3);
     debug.assert(bytes[0] & 0b11110000 == 0b11100000);
     var value: u32 = bytes[0] & 0b00001111;
@@ -104,7 +114,12 @@ pub fn utf8Decode3(bytes: []const u8) !u32 {
     return value;
 }
 
-pub fn utf8Decode4(bytes: []const u8) !u32 {
+const Utf8Decode4Error = error{
+    Utf8ExpectedContinuation,
+    Utf8OverlongEncoding,
+    Utf8CodepointTooLarge,
+};
+pub fn utf8Decode4(bytes: []const u8) Utf8Decode4Error!u32 {
     debug.assert(bytes.len == 4);
     debug.assert(bytes[0] & 0b11111000 == 0b11110000);
     var value: u32 = bytes[0] & 0b00000111;
@@ -206,19 +221,21 @@ const Utf8Iterator = struct {
     pub fn nextCodepoint(it: &Utf8Iterator) ?u32 {
         const slice = it.nextCodepointSlice() ?? return null;
 
-        const r = switch (slice.len) {
-            1 => u32(slice[0]),
-            2 => utf8Decode2(slice),
-            3 => utf8Decode3(slice),
-            4 => utf8Decode4(slice),
+        switch (slice.len) {
+            1 => return u32(slice[0]),
+            2 => return utf8Decode2(slice) catch unreachable,
+            3 => return utf8Decode3(slice) catch unreachable,
+            4 => return utf8Decode4(slice) catch unreachable,
             else => unreachable,
-        };
-
-        return r catch unreachable;
+        }
     }
 };
 
 test "utf8 encode" {
+    comptime testUtf8Encode() catch unreachable;
+    try testUtf8Encode();
+}
+fn testUtf8Encode() !void {
     // A few taken from wikipedia a few taken elsewhere
     var array: [4]u8 = undefined;
     debug.assert((try utf8Encode(try utf8Decode("€"), array[0..])) == 3);
@@ -241,6 +258,10 @@ test "utf8 encode" {
 }
 
 test "utf8 encode error" {
+    comptime testUtf8EncodeError();
+    testUtf8EncodeError();
+}
+fn testUtf8EncodeError() void {
     var array: [4]u8 = undefined;
     testErrorEncode(0xd800, array[0..], error.Utf8CannotEncodeSurrogateHalf);
     testErrorEncode(0xdfff, array[0..], error.Utf8CannotEncodeSurrogateHalf);
@@ -257,6 +278,10 @@ fn testErrorEncode(codePoint: u32, array: []u8, expectedErr: error) void {
 }
 
 test "utf8 iterator on ascii" {
+    comptime testUtf8IteratorOnAscii();
+    testUtf8IteratorOnAscii();
+}
+fn testUtf8IteratorOnAscii() void {
     const s = Utf8View.initComptime("abc");
 
     var it1 = s.iterator();
@@ -273,6 +298,10 @@ test "utf8 iterator on ascii" {
 }
 
 test "utf8 view bad" {
+    comptime testUtf8ViewBad();
+    testUtf8ViewBad();
+}
+fn testUtf8ViewBad() void {
     // Compile-time error.
     // const s3 = Utf8View.initComptime("\xfe\xf2");
 
@@ -281,6 +310,10 @@ test "utf8 view bad" {
 }
 
 test "utf8 view ok" {
+    comptime testUtf8ViewOk();
+    testUtf8ViewOk();
+}
+fn testUtf8ViewOk() void {
     const s = Utf8View.initComptime("東京市");
 
     var it1 = s.iterator();
@@ -297,6 +330,10 @@ test "utf8 view ok" {
 }
 
 test "bad utf8 slice" {
+    comptime testBadUtf8Slice();
+    testBadUtf8Slice();
+}
+fn testBadUtf8Slice() void {
     debug.assert(utf8ValidateSlice("abc"));
     debug.assert(!utf8ValidateSlice("abc\xc0"));
     debug.assert(!utf8ValidateSlice("abc\xc0abc"));
@@ -304,6 +341,10 @@ test "bad utf8 slice" {
 }
 
 test "valid utf8" {
+    comptime testValidUtf8();
+    testValidUtf8();
+}
+fn testValidUtf8() void {
     testValid("\x00", 0x0);
     testValid("\x20", 0x20);
     testValid("\x7f", 0x7f);
@@ -319,6 +360,10 @@ test "valid utf8" {
 }
 
 test "invalid utf8 continuation bytes" {
+    comptime testInvalidUtf8ContinuationBytes();
+    testInvalidUtf8ContinuationBytes();
+}
+fn testInvalidUtf8ContinuationBytes() void {
     // unexpected continuation
     testError("\x80", error.Utf8InvalidStartByte);
     testError("\xbf", error.Utf8InvalidStartByte);
@@ -347,6 +392,10 @@ test "invalid utf8 continuation bytes" {
 }
 
 test "overlong utf8 codepoint" {
+    comptime testOverlongUtf8Codepoint();
+    testOverlongUtf8Codepoint();
+}
+fn testOverlongUtf8Codepoint() void {
     testError("\xc0\x80", error.Utf8OverlongEncoding);
     testError("\xc1\xbf", error.Utf8OverlongEncoding);
     testError("\xe0\x80\x80", error.Utf8OverlongEncoding);
@@ -356,6 +405,10 @@ test "overlong utf8 codepoint" {
 }
 
 test "misc invalid utf8" {
+    comptime testMiscInvalidUtf8();
+    testMiscInvalidUtf8();
+}
+fn testMiscInvalidUtf8() void {
     // codepoint out of bounds
     testError("\xf4\x90\x80\x80", error.Utf8CodepointTooLarge);
     testError("\xf7\xbf\xbf\xbf", error.Utf8CodepointTooLarge);