Add a pretty-printer class to Skylark

With the recording of the results of repository rules (that
eventually will lead to an implementation of the WORKSPACE.resolved
proposal) bazel started writing out lengthy Skylark values. To make
this file more readable for humans, add a Skylkark printer that
does at least some basic line breaking and indenting.

Change-Id: I469d029421df9212b43747509dd17bd6c64da4a8
PiperOrigin-RevId: 198389112

1 files changed, 54 insertions, 0 deletions

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 dfbc651a11..27ded6721d 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
@@ -13,6 +13,7 @@
 // limitations under the License.
 package com.google.devtools.build.lib.syntax;
 
+import com.google.common.base.Strings;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Iterables;
 import com.google.devtools.build.lib.events.Location;
@@ -71,6 +72,15 @@ public class Printer {
   }
 
   /**
+   * Creates an instance of {@link PrettyPrinter} with an empty buffer.
+   *
+   * @return new {@link PrettyPrinter}
+   */
+  public static PrettyPrinter getPrettyPrinter() {
+    return new PrettyPrinter(new StringBuilder());
+  }
+
+  /**
    * Creates an instance of {@link BasePrinter} with an empty buffer and whose format strings allow
    * only %s and %%.
    */
@@ -643,6 +653,50 @@ public class Printer {
     }
   }
 
+
+  /** A printer that breaks lines beteen the entries of lists, with proper indenting. */
+ public static class PrettyPrinter extends BasePrinter {
+    static final int BASE_INDENT = 4;
+    private int indent;
+
+    protected PrettyPrinter(Appendable buffer) {
+      super(buffer);
+      indent = 0;
+    }
+
+    @Override
+    public BasePrinter printList(
+        Iterable<?> list,
+        String before,
+        String untrimmedSeparator,
+        String after,
+        @Nullable String singletonTerminator) {
+
+      String separator = untrimmedSeparator.trim();
+
+      this.append(before + "\n");
+      indent += BASE_INDENT;
+      boolean printSeparator = false; // don't print the separator before the first element
+      int len = 0;
+      for (Object o : list) {
+        if (printSeparator) {
+          this.append(separator + "\n");
+        }
+        this.append(Strings.repeat(" ", indent));
+        this.repr(o);
+        printSeparator = true;
+        len++;
+      }
+      if (singletonTerminator != null && len == 1) {
+        this.append(singletonTerminator);
+      }
+      this.append("\n");
+      indent -= BASE_INDENT;
+      this.append(Strings.repeat(" ", indent) + after);
+      return this;
+    }
+  }
+
   /** A version of {@code BasePrinter} that is able to print abbreviated lists. */
   public static final class LengthLimitedPrinter extends BasePrinter {