After Markus’s review

Author: eggrobin

unicodetools/src/main/java/org/unicode/props/PropertyParsingInfo.java

@@ -49,7 +49,14 @@ enum SpecialProperty {
     public final UcdProperty property;
     public final SpecialProperty special;
 
+    /**
+     * Represents a mapping from one field of a UCD file to another. For instance, given the data
+     * line ABCD ; Value ; 1234 FieldMapping(1) maps U+ABCD to Value, FieldMapping(2) maps U+ABCD to
+     * 1234 (which may be interpreted as U+1234) depending on the property type, and FieldMapping(2,
+     * 1) maps U+1234 to Value.
+     */
     public static class FieldMapping implements Comparable<FieldMapping> {
+        /** A mapping from field 0 to field `valueField`. This is the most common case. */
         FieldMapping(int valueField) {
             this(0, valueField);
         }
@@ -61,15 +68,20 @@ public static class FieldMapping implements Comparable<FieldMapping> {
 
         @Override
         public int compareTo(FieldMapping other) {
-            return Comparator.<FieldMapping>comparingInt(m -> m.keyField)
-                    .thenComparing(m -> m.valueField)
-                    .compare(this, other);
+            return comparator.compare(this, other);
+        }
+
+        @Override
+        public String toString() {
+            return keyField + " ↦ " + valueField;
         }
 
         final int keyField;
         final int valueField;
+        static final Comparator<FieldMapping> comparator =
+                Comparator.<FieldMapping>comparingInt(m -> m.keyField)
+                        .thenComparing(m -> m.valueField);
     }
-    ;
 
     /**
      * Maps from Unicode versions to field mapping. A property whose field mapping depends on the
@@ -696,14 +708,12 @@ static void parseSourceFile(
                             propInfoSet);
                     break;
                 case Field:
+                    final var mapping = propInfo.getFieldMapping(indexUnicodeProperties.ucdVersion);
                     if (propInfoSet.size() == 1
                             && (propInfo = propInfoSet.iterator().next()).special
                                     == SpecialProperty.None
-                            && propInfo.getFieldMapping(indexUnicodeProperties.ucdVersion).keyField
-                                    == 0
-                            && propInfo.getFieldMapping(indexUnicodeProperties.ucdVersion)
-                                            .valueField
-                                    == 1) {
+                            && mapping.keyField == 0
+                            && mapping.valueField == 1) {
                         if (fileName.equals("math/*/MathClass")
                                 && indexUnicodeProperties.ucdVersion.compareTo(
                                                 VersionInfo.UNICODE_6_3)

unicodetools/src/main/resources/org/unicode/props/IndexUnicodeProperties.txt

@@ -45,6 +45,7 @@ FileType ; SealSources ; PropertyValue
 
 FileType ; NameAliases ; NameAliases
 FileType ; NameAliasesProv ; NameAliases
+# TODO(egg): These probably want to be somehow associated with their base character.
 FileType ; StandardizedVariants ; StandardizedVariants
 FileType ; emoji-variation-sequences ; StandardizedVariants
 
@@ -58,6 +59,8 @@ FileType ; CJKRadicals ; CJKRadicals
 # NamedSequences File Type
 # The code point is not in field 0, but instead in field 1.
 # The value is in field 0
+# TODO(egg): This could be handled with a field mapping 1 ↦ 0 instead of a
+# dedicated file type.
 
 FileType ; NamedSequences ; NamedSequences
 FileType ; NamedSequencesProv ; NamedSequences
@@ -70,11 +73,21 @@ FileType ; NamesList ; NamesList
 # =======================================
 
 # Files where particular properties can be found, and in which field
-# The format is:
-# Field0 : file name
-# Field1 : property name
-# Field2 : field number in file (default is 1)
-# Field3 : special handling
+# The format of these property location lines is:
+# <file name without extension>
+#    ; <property alias>
+#  [ ; <field mapping> [ ; <special handling> ] ]
+#  [ ; <version> ]
+# Where <field mapping> is <key field index> ↦ <value field index>
+# or <value field index> (with the key field being field 0 by default).
+# If the <field mapping> is omitted, it is 0 ↦ 1 by default.
+# No <field mapping> is given for files whose type determine the field mapping,
+# such as PropertyValue: in a PropertyValue file, the key is always
+# field 0, the value field 2, and field 1 determines the property.
+# <version> has the form v<n>[.<n>.[.<n>]]; it determines the latest applicable
+# version for a past location of the property.  If it is omitted, the location
+# is still current.
+# The <special handling> is only used for SpecialCasing:
 #   Skip1FT  : Skip line if field 1 is F or T
 #   Skip1ST  : Skip line if field 1 is S or T
 #   SkipAny4 : Skip line if field 4 is not empty