Improve Text.toDisplayString (#5045) (#5598)

engine/runtime/src/main/java/org/enso/interpreter/runtime/data/text/Text.java

@@ -193,19 +193,36 @@ public final class Text implements TruffleObject {
       boolean allowSideEffects,
       @Cached("build()") @Cached.Shared("strings") ToJavaStringNode toJavaStringNode) {
     String str = toJavaStringNode.execute(this);
-    // TODO This should be more extensible
+    int len = str.length();
-    String replaced =
+    int outputLength = len + 2; // Precise if there are no special characters.
-        str.replace("\\", "\\\\")
+
-            .replace("'", "\\'")
+    // TODO This should be more extensible; while it's still a small fixed set,
-            .replace("\n", "\\n")
+    // a switch is probably fastest (unconfirmed)
-            .replace("\t", "\\t")
+
-            .replace("\u0007", "\\a")
+    StringBuffer strBuf = new StringBuffer(outputLength);
-            .replace("\u0008", "\\b")
+
-            .replace("\u000c", "\\f")
+    strBuf.append('\'');
-            .replace("\r", "\\r")
+
-            .replace("\u000B", "\\v")
+    for (int i = 0; i < len; ++i) {
-            .replace("\u001B", "\\e");
+      char c = str.charAt(i);
-    return "'" + replaced + "'";
+      switch (c) {
+        case '\\' -> strBuf.append("\\\\");
+        case '\'' -> strBuf.append("\\'");
+        case '\n' -> strBuf.append("\\n");
+        case '\t' -> strBuf.append("\\t");
+        case '\u0007' -> strBuf.append("\\a");
+        case '\u0008' -> strBuf.append("\\b");
+        case '\u000c' -> strBuf.append("\\f");
+        case '\r' -> strBuf.append("\\r");
+        case '\u000B' -> strBuf.append("\\v");
+        case '\u001B' -> strBuf.append("\\e");
+        default -> strBuf.append(c);
+      }
+    }
+
+    strBuf.append('\'');
+
+    return strBuf.toString();
   }
 
   @ExportMessage

test/Benchmarks/src/Text/Pretty.enso

@@ -0,0 +1,37 @@
+from Standard.Base import all
+
+from Standard.Test import Bench, Faker
+
+# Benchmarks ##################################################################
+
+cycle_character_template num character_templates =
+  character_templates.at (num % (character_templates.length))
+
+bench =
+    ## The `Text.pretty` benchmarks check both scenarios where the Texts are
+       short and very long. This is to verify that making a single pass over
+       the text is in fact faster than multiple passes.
+    bench_pretty suite_prefix =
+        faker = Faker.new
+
+        regular_characters = (Faker.upper_case_letters + Faker.lower_case_letters)
+        # Keep this up to date with the special characters in Text.java
+        special_characters = '\\\'\n\t\u{7}\u{8}\u{c}\r\u{b}\u{1b}'.char_vector
+
+        # 20% special, 80% regular
+        make_template length =
+          r = regular_characters
+          s = special_characters
+          Vector.new length ix-> cycle_character_template ix [r, r, s, s, r]
+
+        very_short_template = make_template 4
+        very_short_random = faker.string_value very_short_template
+        big_template = make_template 100000
+        big_random = faker.string_value big_template
+
+        Bench.measure (very_short_random.pretty) suite_prefix+" 4" 10 10
+        Bench.measure (big_random.pretty) suite_prefix+" 100000" 10 10
+
+    bench_pretty "Text.pretty"
+
+main = bench