config: add string parse, tests

src/config/string.zig

@@ -0,0 +1,67 @@
+const std = @import("std");
+
+/// Parse a string literal into a byte array. The string can contain
+/// any valid Zig string literal escape sequences.
+///
+/// The output buffer never needs sto be larger than the input buffer.
+/// The buffers may alias.
+pub fn parse(out: []u8, bytes: []const u8) ![]u8 {
+    var dst_i: usize = 0;
+    var src_i: usize = 0;
+    while (src_i < bytes.len) {
+        if (dst_i >= out.len) return error.OutOfMemory;
+
+        // If this byte is not beginning an escape sequence we copy.
+        const b = bytes[src_i];
+        if (b != '\\') {
+            out[dst_i] = b;
+            dst_i += 1;
+            src_i += 1;
+            continue;
+        }
+
+        // Parse the escape sequence
+        switch (std.zig.string_literal.parseEscapeSequence(
+            bytes,
+            &src_i,
+        )) {
+            .failure => return error.InvalidString,
+            .success => |cp| dst_i += try std.unicode.utf8Encode(
+                cp,
+                out[dst_i..],
+            ),
+        }
+    }
+
+    return out[0..dst_i];
+}
+
+test "parse: empty" {
+    const testing = std.testing;
+
+    var buf: [128]u8 = undefined;
+    const result = try parse(&buf, "");
+    try testing.expectEqualStrings("", result);
+}
+
+test "parse: no escapes" {
+    const testing = std.testing;
+
+    var buf: [128]u8 = undefined;
+    const result = try parse(&buf, "hello world");
+    try testing.expectEqualStrings("hello world", result);
+}
+
+test "parse: escapes" {
+    const testing = std.testing;
+
+    var buf: [128]u8 = undefined;
+    {
+        const result = try parse(&buf, "hello\\nworld");
+        try testing.expectEqualStrings("hello\nworld", result);
+    }
+    {
+        const result = try parse(&buf, "hello\\u{1F601}world");
+        try testing.expectEqualStrings("hello\u{1F601}world", result);
+    }
+}