Limit the length of the output of Printer.printList().

--
MOS_MIGRATED_REVID=104197461

3 files changed, 188 insertions, 38 deletions

diff --git a/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java b/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java
index 98f498ae9b..56da7abe9b 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/FuncallExpression.java
@@ -273,15 +273,7 @@ public final class FuncallExpression extends Expression {
       sb.append(obj).append(".");
     }
     sb.append(func);
-    String backup = sb.toString();
-    try {
-      Printer.printList(sb, args, "(", ", ", ")", /* singletonTerminator */ null);
-    } catch (OutOfMemoryError ex) {
-      // export_files might lead to an OOM error (e.g. in
-      // PackageSerializationTest#testMassivePackageDeserializesFine).
-      // TODO(b/23967033): make the Printer limit its own output.
-      return backup + "(<too long>)";
-    }
+    Printer.printList(sb, args, "(", ", ", ")", /* singletonTerminator */ null);
     return sb.toString();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/ListLiteral.java b/src/main/java/com/google/devtools/build/lib/syntax/ListLiteral.java
index 22dcec8810..55e855611c 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/ListLiteral.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/ListLiteral.java
@@ -70,33 +70,10 @@ public final class ListLiteral extends Expression {
     return kind == Kind.TUPLE;
   }
 
-  private static char startChar(Kind kind) {
-    switch(kind) {
-    case LIST:  return '[';
-    case TUPLE: return '(';
-    }
-    return '[';
-  }
-
-  private static char endChar(Kind kind) {
-    switch(kind) {
-    case LIST:  return ']';
-    case TUPLE: return ')';
-    }
-    return ']';
-  }
-
   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder();
-    sb.append(startChar(kind));
-    String sep = "";
-    for (Expression e : exprs) {
-      sb.append(sep);
-      sb.append(e);
-      sep = ", ";
-    }
-    sb.append(endChar(kind));
+    Printer.printList(sb, exprs, isTuple(), '"');
     return sb.toString();
   }
 
diff --git a/src/main/java/com/google/devtools/build/lib/syntax/Printer.java b/src/main/java/com/google/devtools/build/lib/syntax/Printer.java
index 0fa29641fe..f607b11253 100644
--- a/src/main/java/com/google/devtools/build/lib/syntax/Printer.java
+++ b/src/main/java/com/google/devtools/build/lib/syntax/Printer.java
@@ -13,7 +13,10 @@
 // limitations under the License.
 package com.google.devtools.build.lib.syntax;
 
+import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.ImmutableList;
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.syntax.SkylarkList.Tuple;
 import com.google.devtools.build.lib.vfs.PathFragment;
 
@@ -27,6 +30,8 @@ import java.util.MissingFormatWidthException;
 import java.util.Set;
 import java.util.SortedMap;
 import java.util.TreeMap;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
 
 /**
  * (Pretty) Printing of Skylark values
@@ -35,6 +40,19 @@ public final class Printer {
 
   private static final char SKYLARK_QUOTATION_MARK = '"';
 
+  /*
+   * Maximum number of list elements that should be printed via printList().
+   */
+  @VisibleForTesting
+  static final int CRITICAL_LIST_ELEMENTS_COUNT = 10;
+
+  /*
+   * printList() will start to shorten the values of list elements when their string length reaches
+   * this value.
+   */
+  @VisibleForTesting
+  static final int CRITICAL_LIST_ELEMENTS_STRING_LENGTH = 128;
+
   private Printer() {
   }
 
@@ -257,21 +275,54 @@ public final class Printer {
       String after,
       String singletonTerminator,
       char quotationMark) {
+    return printList(buffer, list, before, separator, after, singletonTerminator, quotationMark,
+        CRITICAL_LIST_ELEMENTS_COUNT, CRITICAL_LIST_ELEMENTS_STRING_LENGTH);
+  }
+
+  private static Appendable printList(
+      Appendable buffer,
+      Iterable<?> list,
+      String before,
+      String separator,
+      String after,
+      String singletonTerminator,
+      char quotationMark,
+      int maxItemsToPrint,
+      int criticalItemsStringLength) {
     boolean printSeparator = false; // don't print the separator before the first element
+    boolean skipArgs = false;
+    int items = Iterables.size(list);
     int len = 0;
-    append(buffer, before);
+    // We don't want to print "1 more arguments", hence we don't skip arguments if there is only one
+    // above the limit.
+    int itemsToPrint = (items - maxItemsToPrint == 1) ? items : maxItemsToPrint;
+
+    LengthLimitedAppendable appendable =
+        LengthLimitedAppendable.create(buffer, criticalItemsStringLength);
+    append(appendable, before);
+    appendable.enforceLimit();
     for (Object o : list) {
+      // We don't want to print "1 more arguments", even if we hit the string limit.
+      if (len == itemsToPrint || (appendable.hasHitLimit() && len < items - 1)) {
+        skipArgs = true;
+        break;
+      }
       if (printSeparator) {
-        append(buffer, separator);
+        append(appendable, separator);
       }
-      write(buffer, o, quotationMark);
+      write(appendable, o, quotationMark);
       printSeparator = true;
       len++;
     }
+    appendable.ignoreLimit();
+    if (skipArgs) {
+      append(appendable, separator);
+      append(appendable, String.format("<%d more arguments>", items - len));
+    }
     if (singletonTerminator != null && len == 1) {
-      append(buffer, singletonTerminator);
+      append(appendable, singletonTerminator);
     }
-    return append(buffer, after);
+    return append(appendable, after);
   }
 
   public static Appendable printList(Appendable buffer, Iterable<?> list, String before,
@@ -443,4 +494,134 @@ public final class Printer {
     }
     return buffer;
   }
+
+  /**
+   * Helper class for {@code Appendable}s that want to limit the length of their input.
+   *
+   * <p>Instances of this class act as a proxy for one {@code Appendable} object and decide whether
+   * the given input (or parts of it) can be written to the underlying {@code Appendable}, depending
+   * on whether the specified maximum length has been met or not.
+   */
+  private static final class LengthLimitedAppendable implements Appendable {
+
+    private static final ImmutableSet<Character> SPECIAL_CHARS =
+        ImmutableSet.of(',', ' ', '"', '\'', ':', '(', ')', '[', ']', '{', '}');
+
+    private static final Pattern ARGS_PATTERN = Pattern.compile("<\\d+ more arguments>");
+
+    private final Appendable original;
+    private int limit;
+    private boolean ignoreLimit;
+    private boolean previouslyShortened;
+    
+    private LengthLimitedAppendable(Appendable original, int limit) {
+      this.original = original;
+      this.limit = limit;
+    }
+
+    public static LengthLimitedAppendable create(Appendable original, int limit) {
+      // We don't want to overwrite the limit if original is already an instance of this class.
+      return (original instanceof LengthLimitedAppendable)
+          ? (LengthLimitedAppendable) original : new LengthLimitedAppendable(original, limit);
+    }
+
+    @Override
+    public Appendable append(CharSequence csq) throws IOException {
+      if (ignoreLimit || hasOnlySpecialChars(csq)) {
+        // Don't update limit.
+        original.append(csq);
+        previouslyShortened = false;
+      } else {
+        int length = csq.length();
+        if (length <= limit) {
+          limit -= length;
+          original.append(csq);
+        } else {
+          original.append(csq, 0, limit);
+          // We don't want to append multiple ellipses.
+          if (!previouslyShortened) {
+            original.append("...");
+          }
+          appendTrailingSpecialChars(csq, limit);
+          previouslyShortened = true;
+          limit = 0;
+        }
+      }
+      return this;
+    }
+
+    /**
+     * Appends any trailing "special characters" (e.g. brackets, quotation marks) in the given
+     * sequence to the output buffer, regardless of the limit.
+     *
+     * <p>For example, let's look at foo(['too long']). Without this method, the shortened result
+     * would be foo(['too...) instead of the prettier foo(['too...']).
+     *
+     * <p>If the input string was already shortened and contains "<x more arguments>", this part
+     * will also be appended.
+     */
+    private void appendTrailingSpecialChars(CharSequence csq, int limit) throws IOException {
+      int length = csq.length();
+      Matcher matcher = ARGS_PATTERN.matcher(csq);
+      // We assume that everything following the "x more arguments" part has to be copied, too.
+      int start = matcher.find() ? matcher.start() : length;
+      // Find the left-most non-arg char that has to be copied.
+      for (int i = start - 1; i > limit; --i) {
+        if (isSpecialChar(csq.charAt(i))) {
+          start = i;
+        } else {
+          break;
+        }
+      }
+      if (start < length) {
+        original.append(csq, start, csq.length());
+      }
+    }
+
+    /**
+     * Returns whether the given sequence denotes characters that are not part of the value of an
+     * argument.
+     *
+     * <p>Examples are brackets, braces and quotation marks.
+     */
+    private boolean hasOnlySpecialChars(CharSequence csq) {
+      for (int i = 0; i < csq.length(); ++i) {
+        if (!isSpecialChar(csq.charAt(i))) {
+          return false;
+        }
+      }
+      return true;
+    }
+
+    private boolean isSpecialChar(char c)    {
+      return SPECIAL_CHARS.contains(c);
+    }
+
+    @Override
+    public Appendable append(CharSequence csq, int start, int end) throws IOException {
+      return append(csq.subSequence(start, end));
+    }
+
+    @Override
+    public Appendable append(char c) throws IOException {
+      return append(String.valueOf(c));
+    }
+    
+    public boolean hasHitLimit()  {
+      return limit <= 0;
+    }
+
+    public void enforceLimit()  {
+      ignoreLimit = false;
+    }
+    
+    public void ignoreLimit() {
+      ignoreLimit = true;
+    }
+
+    @Override
+    public String toString() {
+      return original.toString();
+    }
+  }
 }