Text.to_display_text is (shortened) identity

engine/runtime/src/main/java/org/enso/interpreter/node/expression/builtin/text/AnyToDisplayTextNode.java

@@ -1,5 +1,7 @@
 package org.enso.interpreter.node.expression.builtin.text;
 
+import com.ibm.icu.text.BreakIterator;
+import com.oracle.truffle.api.CompilerDirectives;
 import com.oracle.truffle.api.dsl.Cached;
 import com.oracle.truffle.api.dsl.Fallback;
 import com.oracle.truffle.api.dsl.Specialization;
@@ -11,6 +13,7 @@
 import org.enso.interpreter.dsl.BuiltinMethod;
 import org.enso.interpreter.node.expression.builtin.text.util.TypeToDisplayTextNode;
 import org.enso.interpreter.runtime.data.text.Text;
+import org.enso.polyglot.common_utils.Core_Text_Utils;
 
 @BuiltinMethod(type = "Any", name = "to_display_text")
 public abstract class AnyToDisplayTextNode extends Node {
@@ -32,6 +35,22 @@ Text showExceptions(
     }
   }
 
+  @Specialization
+  Text convertText(Text self) {
+    final var limit = 80;
+    if (self.length() < limit) {
+      return self;
+    } else {
+      return takePrefix(self, limit);
+    }
+  }
+
+  @CompilerDirectives.TruffleBoundary
+  private static Text takePrefix(Text self, final int limit) {
+    var prefix = Core_Text_Utils.take_prefix(self.toString(), limit);
+    return Text.create(prefix);
+  }
+
   @Fallback
   Text doShowType(Object self, @Cached TypeToDisplayTextNode typeToDisplayTextNode) {
     return Text.create(typeToDisplayTextNode.execute(self));

lib/scala/common-polyglot-core-utils/src/main/java/org/enso/polyglot/common_utils/Core_Text_Utils.java

@@ -3,6 +3,9 @@
 import com.ibm.icu.text.BreakIterator;
 
 public class Core_Text_Utils {
+  private Core_Text_Utils() {
+  }
+
   /** Computes the length of the string as the number of grapheme clusters it contains. */
   public static int computeGraphemeLength(String text) {
     BreakIterator iter = BreakIterator.getCharacterInstance();
@@ -14,6 +17,17 @@ public static int computeGraphemeLength(String text) {
     return len;
   }
 
+  /** Returns a prefix of the string not exceeding the provided grapheme length. */
+  public static String take_prefix(String str, long grapheme_length) {
+    BreakIterator iter = BreakIterator.getCharacterInstance();
+    iter.setText(str);
+    if (iter.next(Math.toIntExact(grapheme_length)) == BreakIterator.DONE) {
+      return str;
+    } else {
+      return str.substring(0, iter.current());
+    }
+  }
+
   /** Pretty prints the string, escaping special characters. */
   public static String prettyPrint(String str) {
     int len = str.length();

std-bits/base/src/main/java/org/enso/base/Text_Utils.java

@@ -277,13 +277,7 @@ public static long grapheme_length(String str) {
 
   /** Returns a prefix of the string not exceeding the provided grapheme length. */
   public static String take_prefix(String str, long grapheme_length) {
-    BreakIterator iter = BreakIterator.getCharacterInstance();
-    iter.setText(str);
-    if (iter.next(Math.toIntExact(grapheme_length)) == BreakIterator.DONE) {
-      return str;
-    } else {
-      return str.substring(0, iter.current());
-    }
+    return Core_Text_Utils.take_prefix(str, grapheme_length);
   }
 
   /** Returns a suffix of the string not exceeding the provided grapheme length. */

test/Tests/src/Data/Text/Utils_Spec.enso

@@ -89,4 +89,27 @@ spec =
             Text_Utils.take_suffix (kshi+kshi+'a'+kshi) 2 . should_equal 'a'+kshi
             Text_Utils.take_suffix (kshi+kshi+'a'+kshi) 1 . should_equal kshi
 
+    Test.group "to_display_text" <|
+        Test.specify "simple conversion" <|
+            "Hello".to_display_text . should_equal "Hello"
+
+        Test.specify "long text conversion" <|
+            long = "Hello World! ".repeat 1024
+            disp = long.to_display_text
+            disp.length . should_equal 80
+            disp.characters.take (First 5) . should_equal [ 'H', 'e', 'l', 'l', 'o' ]
+            disp.characters.take (Last 6) . should_equal ['l', 'd', '!', ' ', 'H', 'e']
+
+        Test.specify "grapheme 1 conversion" <|
+            txt = 'a\u0321\u0302'*100
+            txt.to_display_text . should_equal 'a\u0321\u0302'*80
+
+        Test.specify "grapheme 2 conversion" <|
+            txt = '\u0915\u094D\u0937\u093F'*100
+            txt.to_display_text . should_equal '\u0915\u094D\u0937\u093F'*80
+
+        Test.specify "grapheme 3 conversion" <|
+            txt = '\u{1F926}\u{1F3FC}\u200D\u2642\uFE0F'*100
+            txt.to_display_text . should_equal '\u{1F926}\u{1F3FC}\u200D\u2642\uFE0F'*80
+
 main = Test_Suite.run_main spec