src/main/java/com/google/devtools/build/lib/syntax/Printer.java - bazel - Git at Google

 // Copyright 2015 The Bazel Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //    http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 package com.google.devtools.build.lib.syntax;

 import com.google.common.base.Strings;
 import com.google.devtools.build.lib.events.Location;
 import com.google.devtools.build.lib.skylarkinterface.SkylarkPrinter;
 import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;
 import java.io.IOException;
 import java.util.Arrays;
 import java.util.Formattable;
 import java.util.Formatter;
 import java.util.IllegalFormatException;
 import java.util.List;
 import java.util.Map;
 import java.util.MissingFormatWidthException;
 import java.util.UnknownFormatConversionException;
 import javax.annotation.Nullable;

 /** (Pretty) Printing of Skylark values */
 public class Printer {

   /**
    * Creates an instance of {@link BasePrinter} that wraps an existing buffer.
    *
    * @param buffer an {@link Appendable}
    * @return new {@link BasePrinter}
    */
   static BasePrinter getPrinter(Appendable buffer) {
     return new BasePrinter(buffer);
   }

   /**
    * Creates an instance of {@link BasePrinter} with an empty buffer.
    *
    * @return new {@link BasePrinter}
    */
   public static BasePrinter getPrinter() {
     return new BasePrinter(new StringBuilder());
   }

   /**
    * 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 %%.
    */
   public static BasePrinter getSimplifiedPrinter() {
     return new BasePrinter(new StringBuilder(), /*simplifiedFormatStrings=*/ true);
   }

   private Printer() {}

   // These static methods proxy to the similar methods of BasePrinter

   /** Format an object with Skylark's {@code debugPrint}. */
   static String debugPrint(Object x) {
     return getPrinter().debugPrint(x).toString();
   }

   /**
    * Perform Python-style string formatting, lazily.
    *
    * @param pattern a format string.
    * @param arguments positional arguments.
    * @return the formatted string.
    */
   static Formattable formattable(final String pattern, Object... arguments) {
     final List<Object> args = Arrays.asList(arguments);
     return new Formattable() {
       @Override
       public String toString() {
         return Starlark.formatWithList(pattern, args);
       }

       @Override
       public void formatTo(Formatter formatter, int flags, int width, int precision) {
         Printer.getPrinter(formatter.out()).formatWithList(pattern, args);
       }
     };
   }

   /**
    * Append a char to a buffer. In case of {@link IOException} throw an {@link AssertionError}
    * instead
    *
    * @return buffer
    */
   private static Appendable append(Appendable buffer, char c) {
     try {
       return buffer.append(c);
     } catch (IOException e) {
       throw new AssertionError(e);
     }
   }

   /**
    * Append a char sequence to a buffer. In case of {@link IOException} throw an {@link
    * AssertionError} instead
    *
    * @return buffer
    */
   private static Appendable append(Appendable buffer, CharSequence s) {
     try {
       return buffer.append(s);
     } catch (IOException e) {
       throw new AssertionError(e);
     }
   }

   /**
    * Append a char sequence range to a buffer. In case of {@link IOException} throw an
    * {@link AssertionError} instead
    * @return buffer
    */
   private static Appendable append(Appendable buffer, CharSequence s, int start, int end) {
     try {
       return buffer.append(s, start, end);
     } catch (IOException e) {
       throw new AssertionError(e);
     }
   }

   /** Actual class that implements Printer API */
   public static class BasePrinter implements SkylarkPrinter {
     // Methods of this class should not recurse through static methods of Printer

     protected final Appendable buffer;

     /**
      * If true, the only percent sequences allowed in format strings are %s substitutions and %%
      * escapes.
      */
     protected final boolean simplifiedFormatStrings;

     /**
      * Creates a printer.
      *
      * @param buffer the {@link Appendable} that will be written to
      * @param simplifiedFormatStrings if true, format strings will allow only %s and %%
      */
     protected BasePrinter(Appendable buffer, boolean simplifiedFormatStrings) {
       this.buffer = buffer;
       this.simplifiedFormatStrings = simplifiedFormatStrings;
     }

     /**
      * Creates a printer that writes to the given buffer and that does not use simplified format
      * strings.
      */
     protected BasePrinter(Appendable buffer) {
       this(buffer, /*simplifiedFormatStrings=*/ false);
     }

     /**
      * Creates a printer that uses a fresh buffer and that does not use simplified format strings.
      */
     protected BasePrinter() {
       this(new StringBuilder());
     }

     @Override
     public String toString() {
       return buffer.toString();
     }

     /**
      * Print an informal debug-only representation of object x.
      *
      * @param o the object
      * @return the buffer, in fluent style
      */
     public BasePrinter debugPrint(Object o) {
       if (o instanceof SkylarkValue) {
         ((SkylarkValue) o).debugPrint(this);
         return this;
       }

       return this.str(o);
     }

     /**
      * Prints the informal representation of value {@code o}. Unlike {@code repr(x)}, it does not
      * quote strings at top level, though strings and other values appearing as elements of other
      * structures are quoted as if by {@code repr}.
      *
      * <p>Implementations of SkylarkValue may define their own behavior of {@code str}.
      */
     public BasePrinter str(Object o) {
       if (o instanceof SkylarkValue) {
         ((SkylarkValue) o).str(this);
         return this;
       }

       if (o instanceof String) {
         return this.append((String) o);
       }
       return this.repr(o);
     }

     /**
      * Prints the quoted representation of Starlark value {@code o}. The quoted form is often a
      * Starlark expression that evaluates to {@code o}.
      *
      * <p>Implementations of SkylarkValue may define their own behavior of {@code repr}.
      *
      * <p>In addition to Starlark values, {@code repr} also prints instances of classes Map, List,
      * Map.Entry, Class, Node, or Location. To avoid nondeterminism, all other values are printed
      * opaquely.
      */
     @Override
     public BasePrinter repr(Object o) {
       if (o == null) {
         // Java null is not a valid Skylark value, but sometimes printers are used on non-Skylark
         // values such as Locations or ASTs.
         this.append("null");

       } else if (o instanceof SkylarkValue) {
         ((SkylarkValue) o).repr(this);

       } else if (o instanceof String) {
         writeString((String) o);

       } else if (o instanceof Integer || o instanceof Double) {
         this.append(o.toString());

       } else if (Boolean.TRUE.equals(o)) {
         this.append("True");

       } else if (Boolean.FALSE.equals(o)) {
         this.append("False");

         // -- non-Starlark values --

       } else if (o instanceof Map<?, ?>) {
         Map<?, ?> dict = (Map<?, ?>) o;
         this.printList(dict.entrySet(), "{", ", ", "}", null);

       } else if (o instanceof List<?>) {
         List<?> seq = (List<?>) o;
         this.printList(seq, false);

       } else if (o instanceof Map.Entry<?, ?>) {
         Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
         this.repr(entry.getKey());
         this.append(": ");
         this.repr(entry.getValue());

       } else if (o instanceof Class<?>) {
         this.append(EvalUtils.getDataTypeNameFromClass((Class<?>) o));

       } else if (o instanceof Node || o instanceof Location) {
         // AST node objects and locations are printed in tracebacks and error messages,
         // it's safe to print their toString representations
         this.append(o.toString());

       } else {
         // For now, we print all unknown values opaquely.
         // Historically this was a defense against accidental nondeterminism,
         // but Starlark code cannot access values of o that would reach here,
         // and native code is already trusted to be deterministic.
         // TODO(adonovan): replace this with a default behavior of this.append(o),
         // once we require that all @Skylark-annotated classes implement SkylarkValue.
         // (After all, Java code can call String.format, which also calls toString.)
         this.append("<unknown object " + o.getClass().getName() + ">");
       }

       return this;
     }

     /**
      * Write a properly escaped Skylark representation of a string to a buffer.
      *
      * @param s the string a representation of which to repr.
      * @return this printer.
      */
     protected BasePrinter writeString(String s) {
       this.append('"');
       int len = s.length();
       for (int i = 0; i < len; i++) {
         char c = s.charAt(i);
         escapeCharacter(c);
       }
       return this.append('"');
     }

     private BasePrinter backslashChar(char c) {
       return this.append('\\').append(c);
     }

     private BasePrinter escapeCharacter(char c) {
       if (c == '"') {
         return backslashChar(c);
       }
       switch (c) {
         case '\\':
           return backslashChar('\\');
         case '\r':
           return backslashChar('r');
         case '\n':
           return backslashChar('n');
         case '\t':
           return backslashChar('t');
         default:
           if (c < 32) {
             //TODO(bazel-team): support \x escapes
             return this.append(String.format("\\x%02x", (int) c));
           }
           return this.append(c); // no need to support UTF-8
       } // endswitch
     }

     /**
      * Print a list of object representations
      *
      * @param list the list of objects to repr (each as with repr)
      * @param before a string to print before the list items, e.g. an opening bracket
      * @param separator a separator to print between items
      * @param after a string to print after the list items, e.g. a closing bracket
      * @param singletonTerminator null or a string to print after the list if it is a singleton The
      *     singleton case is notably relied upon in python syntax to distinguish a tuple of size one
      *     such as ("foo",) from a merely parenthesized object such as ("foo").
      * @return this printer.
      */
     @Override
     public BasePrinter printList(
         Iterable<?> list,
         String before,
         String separator,
         String after,
         @Nullable String singletonTerminator) {

       this.append(before);
       int len = appendListElements(list, separator);
       if (singletonTerminator != null && len == 1) {
         this.append(singletonTerminator);
       }
       return this.append(after);
     }

     /**
      * Appends the given elements to the specified {@link Appendable} and returns the number of
      * elements.
      */
     private int appendListElements(Iterable<?> list, String separator) {
       boolean printSeparator = false; // don't print the separator before the first element
       int len = 0;
       for (Object o : list) {
         if (printSeparator) {
           this.append(separator);
         }
         this.repr(o);
         printSeparator = true;
         len++;
       }
       return len;
     }

     /**
      * Print a Skylark list or tuple of object representations
      *
      * @param list the contents of the list or tuple
      * @param isTuple if true the list will be formatted with parentheses and with a trailing comma
      *     in case of one-element tuples. 'Soft' means that this limit may be exceeded because of
      *     formatting.
      * @return this printer.
      */
     @Override
     public BasePrinter printList(Iterable<?> list, boolean isTuple) {
       if (isTuple) {
         return this.printList(list, "(", ", ", ")", ",");
       } else {
         return this.printList(list, "[", ", ", "]", null);
       }
     }

     /**
      * Perform Python-style string formatting, similar to the {@code pattern % tuple} syntax.
      *
      * <p>The only supported placeholder patterns are
      * <ul>
      *   <li>{@code %s} (convert as if by {@code str()})
      *   <li>{@code %r} (convert as if by {@code repr()})
      *   <li>{@code %d} (convert an integer to its decimal representation)
      * </ul>
      * To encode a literal percent character, escape it as {@code %%}. It is an error to have a
      * non-escaped {@code %} at the end of the string or followed by any character not listed above.
      *
      * <p>If this printer has {@code simplifiedFormatStrings} set, only {@code %s} and {@code %%}
      * are permitted.
      *
      * @param pattern a format string that may contain placeholders
      * @param arguments an array containing arguments to substitute into the placeholders in order
      * @return the formatted string
      * @throws IllegalFormatException if {@code pattern} is not a valid format string, or if
      *     {@code arguments} mismatches the number or type of placeholders in {@code pattern}
      */
     @Override
     public BasePrinter format(String pattern, Object... arguments) {
       return this.formatWithList(pattern, Arrays.asList(arguments));
     }

     /**
      * Perform Python-style string formatting, similar to the {@code pattern % tuple} syntax.
      *
      * <p>Same as {@link #format(String, Object...)}, but with a list instead of variadic args.
      */
     @Override
     public BasePrinter formatWithList(String pattern, List<?> arguments) {
       // TODO(bazel-team): support formatting arguments, and more complex Python patterns.
       // N.B. MissingFormatWidthException is the only kind of IllegalFormatException
       // whose constructor can take and display arbitrary error message, hence its use below.

       int length = pattern.length();
       int argLength = arguments.size();
       int i = 0; // index of next character in pattern
       int a = 0; // index of next argument in arguments

       while (i < length) {
         int p = pattern.indexOf('%', i);
         if (p == -1) {
           Printer.append(buffer, pattern, i, length);
           break;
         }
         if (p > i) {
           Printer.append(buffer, pattern, i, p);
         }
         if (p == length - 1) {
           throw new MissingFormatWidthException(
               "incomplete format pattern ends with %: " + this.repr(pattern));
         }
         char directive = pattern.charAt(p + 1);
         i = p + 2;
         switch (directive) {
           case '%':
             this.append('%');
             continue;
           case 'd':
           case 'r':
           case 's':
             if (simplifiedFormatStrings && (directive != 's')) {
               throw new UnknownFormatConversionException(
                   "cannot use %" + directive + " substitution placeholder when "
                       + "simplifiedFormatStrings is set");
             }
             if (a >= argLength) {
               throw new MissingFormatWidthException(
                   "not enough arguments for format pattern "
                       + Starlark.repr(pattern)
                       + ": "
                       + Starlark.repr(Tuple.copyOf(arguments)));
             }
             Object argument = arguments.get(a++);
             switch (directive) {
               case 'd':
                 if (argument instanceof Integer) {
                   this.append(argument.toString());
                   continue;
                 } else {
                   throw new MissingFormatWidthException(
                       "invalid argument " + Starlark.repr(argument) + " for format pattern %d");
                 }
               case 'r':
                 this.repr(argument);
                 continue;
               case 's':
                 this.str(argument);
                 continue;
             }
             // fall through
           default:
             throw new MissingFormatWidthException(
                 // The call to Starlark.repr doesn't cause an infinite recursion because it's
                 // only used to format a string properly
                 String.format(
                     "unsupported format character \"%s\" at index %s in %s",
                     String.valueOf(directive), p + 1, Starlark.repr(pattern)));
         }
       }
       if (a < argLength) {
         throw new MissingFormatWidthException(
             "not all arguments converted during string formatting");
       }
       return this;
     }

     @Override
     public BasePrinter append(char c) {
       Printer.append(buffer, c);
       return this;
     }

     @Override
     public BasePrinter append(CharSequence s) {
       Printer.append(buffer, s);
       return this;
     }

     BasePrinter append(CharSequence sequence, int start, int end) {
       return this.append(sequence.subSequence(start, end));
     }
   }

   /** A printer that breaks lines between 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) {

       // If the list is empty, do not split the presentation over
       // several lines.
       if (!list.iterator().hasNext()) {
         this.append(before + after);
         return this;
       }

       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;
     }
   }
 }
	// Copyright 2015 The Bazel Authors. All rights reserved.
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	package com.google.devtools.build.lib.syntax;

	import com.google.common.base.Strings;
	import com.google.devtools.build.lib.events.Location;
	import com.google.devtools.build.lib.skylarkinterface.SkylarkPrinter;
	import com.google.devtools.build.lib.skylarkinterface.SkylarkValue;
	import java.io.IOException;
	import java.util.Arrays;
	import java.util.Formattable;
	import java.util.Formatter;
	import java.util.IllegalFormatException;
	import java.util.List;
	import java.util.Map;
	import java.util.MissingFormatWidthException;
	import java.util.UnknownFormatConversionException;
	import javax.annotation.Nullable;

	/** (Pretty) Printing of Skylark values */
	public class Printer {

	/**
	* Creates an instance of {@link BasePrinter} that wraps an existing buffer.
	*
	* @param buffer an {@link Appendable}
	* @return new {@link BasePrinter}
	*/
	static BasePrinter getPrinter(Appendable buffer) {
	return new BasePrinter(buffer);
	}

	/**
	* Creates an instance of {@link BasePrinter} with an empty buffer.
	*
	* @return new {@link BasePrinter}
	*/
	public static BasePrinter getPrinter() {
	return new BasePrinter(new StringBuilder());
	}

	/**
	* 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 %%.
	*/
	public static BasePrinter getSimplifiedPrinter() {
	return new BasePrinter(new StringBuilder(), /simplifiedFormatStrings=/ true);
	}

	private Printer() {}

	// These static methods proxy to the similar methods of BasePrinter

	/** Format an object with Skylark's {@code debugPrint}. */
	static String debugPrint(Object x) {
	return getPrinter().debugPrint(x).toString();
	}

	/**
	* Perform Python-style string formatting, lazily.
	*
	* @param pattern a format string.
	* @param arguments positional arguments.
	* @return the formatted string.
	*/
	static Formattable formattable(final String pattern, Object... arguments) {
	final List<Object> args = Arrays.asList(arguments);
	return new Formattable() {
	@Override
	public String toString() {
	return Starlark.formatWithList(pattern, args);
	}

	@Override
	public void formatTo(Formatter formatter, int flags, int width, int precision) {
	Printer.getPrinter(formatter.out()).formatWithList(pattern, args);
	}
	};
	}

	/**
	* Append a char to a buffer. In case of {@link IOException} throw an {@link AssertionError}
	* instead
	*
	* @return buffer
	*/
	private static Appendable append(Appendable buffer, char c) {
	try {
	return buffer.append(c);
	} catch (IOException e) {
	throw new AssertionError(e);
	}
	}

	/**
	* Append a char sequence to a buffer. In case of {@link IOException} throw an {@link
	* AssertionError} instead
	*
	* @return buffer
	*/
	private static Appendable append(Appendable buffer, CharSequence s) {
	try {
	return buffer.append(s);
	} catch (IOException e) {
	throw new AssertionError(e);
	}
	}

	/**
	* Append a char sequence range to a buffer. In case of {@link IOException} throw an
	* {@link AssertionError} instead
	* @return buffer
	*/
	private static Appendable append(Appendable buffer, CharSequence s, int start, int end) {
	try {
	return buffer.append(s, start, end);
	} catch (IOException e) {
	throw new AssertionError(e);
	}
	}

	/** Actual class that implements Printer API */
	public static class BasePrinter implements SkylarkPrinter {
	// Methods of this class should not recurse through static methods of Printer

	protected final Appendable buffer;

	/**
	* If true, the only percent sequences allowed in format strings are %s substitutions and %%
	* escapes.
	*/
	protected final boolean simplifiedFormatStrings;

	/**
	* Creates a printer.
	*
	* @param buffer the {@link Appendable} that will be written to
	* @param simplifiedFormatStrings if true, format strings will allow only %s and %%
	*/
	protected BasePrinter(Appendable buffer, boolean simplifiedFormatStrings) {
	this.buffer = buffer;
	this.simplifiedFormatStrings = simplifiedFormatStrings;
	}

	/**
	* Creates a printer that writes to the given buffer and that does not use simplified format
	* strings.
	*/
	protected BasePrinter(Appendable buffer) {
	this(buffer, /simplifiedFormatStrings=/ false);
	}

	/**
	* Creates a printer that uses a fresh buffer and that does not use simplified format strings.
	*/
	protected BasePrinter() {
	this(new StringBuilder());
	}

	@Override
	public String toString() {
	return buffer.toString();
	}

	/**
	* Print an informal debug-only representation of object x.
	*
	* @param o the object
	* @return the buffer, in fluent style
	*/
	public BasePrinter debugPrint(Object o) {
	if (o instanceof SkylarkValue) {
	((SkylarkValue) o).debugPrint(this);
	return this;
	}

	return this.str(o);
	}

	/**
	* Prints the informal representation of value {@code o}. Unlike {@code repr(x)}, it does not
	* quote strings at top level, though strings and other values appearing as elements of other
	* structures are quoted as if by {@code repr}.
	*
	* <p>Implementations of SkylarkValue may define their own behavior of {@code str}.
	*/
	public BasePrinter str(Object o) {
	if (o instanceof SkylarkValue) {
	((SkylarkValue) o).str(this);
	return this;
	}

	if (o instanceof String) {
	return this.append((String) o);
	}
	return this.repr(o);
	}

	/**
	* Prints the quoted representation of Starlark value {@code o}. The quoted form is often a
	* Starlark expression that evaluates to {@code o}.
	*
	* <p>Implementations of SkylarkValue may define their own behavior of {@code repr}.
	*
	* <p>In addition to Starlark values, {@code repr} also prints instances of classes Map, List,
	* Map.Entry, Class, Node, or Location. To avoid nondeterminism, all other values are printed
	* opaquely.
	*/
	@Override
	public BasePrinter repr(Object o) {
	if (o == null) {
	// Java null is not a valid Skylark value, but sometimes printers are used on non-Skylark
	// values such as Locations or ASTs.
	this.append("null");

	} else if (o instanceof SkylarkValue) {
	((SkylarkValue) o).repr(this);

	} else if (o instanceof String) {
	writeString((String) o);

	} else if (o instanceof Integer \|\| o instanceof Double) {
	this.append(o.toString());

	} else if (Boolean.TRUE.equals(o)) {
	this.append("True");

	} else if (Boolean.FALSE.equals(o)) {
	this.append("False");

	// -- non-Starlark values --

	} else if (o instanceof Map<?, ?>) {
	Map<?, ?> dict = (Map<?, ?>) o;
	this.printList(dict.entrySet(), "{", ", ", "}", null);

	} else if (o instanceof List<?>) {
	List<?> seq = (List<?>) o;
	this.printList(seq, false);

	} else if (o instanceof Map.Entry<?, ?>) {
	Map.Entry<?, ?> entry = (Map.Entry<?, ?>) o;
	this.repr(entry.getKey());
	this.append(": ");
	this.repr(entry.getValue());

	} else if (o instanceof Class<?>) {
	this.append(EvalUtils.getDataTypeNameFromClass((Class<?>) o));

	} else if (o instanceof Node \|\| o instanceof Location) {
	// AST node objects and locations are printed in tracebacks and error messages,
	// it's safe to print their toString representations
	this.append(o.toString());

	} else {
	// For now, we print all unknown values opaquely.
	// Historically this was a defense against accidental nondeterminism,
	// but Starlark code cannot access values of o that would reach here,
	// and native code is already trusted to be deterministic.
	// TODO(adonovan): replace this with a default behavior of this.append(o),
	// once we require that all @Skylark-annotated classes implement SkylarkValue.
	// (After all, Java code can call String.format, which also calls toString.)
	this.append("<unknown object " + o.getClass().getName() + ">");
	}

	return this;
	}

	/**
	* Write a properly escaped Skylark representation of a string to a buffer.
	*
	* @param s the string a representation of which to repr.
	* @return this printer.
	*/
	protected BasePrinter writeString(String s) {
	this.append('"');
	int len = s.length();
	for (int i = 0; i < len; i++) {
	char c = s.charAt(i);
	escapeCharacter(c);
	}
	return this.append('"');
	}

	private BasePrinter backslashChar(char c) {
	return this.append('\\').append(c);
	}

	private BasePrinter escapeCharacter(char c) {
	if (c == '"') {
	return backslashChar(c);
	}
	switch (c) {
	case '\\':
	return backslashChar('\\');
	case '\r':
	return backslashChar('r');
	case '\n':
	return backslashChar('n');
	case '\t':
	return backslashChar('t');
	default:
	if (c < 32) {
	//TODO(bazel-team): support \x escapes
	return this.append(String.format("\\x%02x", (int) c));
	}
	return this.append(c); // no need to support UTF-8
	} // endswitch
	}

	/**
	* Print a list of object representations
	*
	* @param list the list of objects to repr (each as with repr)
	* @param before a string to print before the list items, e.g. an opening bracket
	* @param separator a separator to print between items
	* @param after a string to print after the list items, e.g. a closing bracket
	* @param singletonTerminator null or a string to print after the list if it is a singleton The
	* singleton case is notably relied upon in python syntax to distinguish a tuple of size one
	* such as ("foo",) from a merely parenthesized object such as ("foo").
	* @return this printer.
	*/
	@Override
	public BasePrinter printList(
	Iterable<?> list,
	String before,
	String separator,
	String after,
	@Nullable String singletonTerminator) {

	this.append(before);
	int len = appendListElements(list, separator);
	if (singletonTerminator != null && len == 1) {
	this.append(singletonTerminator);
	}
	return this.append(after);
	}

	/**
	* Appends the given elements to the specified {@link Appendable} and returns the number of
	* elements.
	*/
	private int appendListElements(Iterable<?> list, String separator) {
	boolean printSeparator = false; // don't print the separator before the first element
	int len = 0;
	for (Object o : list) {
	if (printSeparator) {
	this.append(separator);
	}
	this.repr(o);
	printSeparator = true;
	len++;
	}
	return len;
	}

	/**
	* Print a Skylark list or tuple of object representations
	*
	* @param list the contents of the list or tuple
	* @param isTuple if true the list will be formatted with parentheses and with a trailing comma
	* in case of one-element tuples. 'Soft' means that this limit may be exceeded because of
	* formatting.
	* @return this printer.
	*/
	@Override
	public BasePrinter printList(Iterable<?> list, boolean isTuple) {
	if (isTuple) {
	return this.printList(list, "(", ", ", ")", ",");
	} else {
	return this.printList(list, "[", ", ", "]", null);
	}
	}

	/**
	* Perform Python-style string formatting, similar to the {@code pattern % tuple} syntax.
	*
	* <p>The only supported placeholder patterns are
	* <ul>
	* <li>{@code %s} (convert as if by {@code str()})
	* <li>{@code %r} (convert as if by {@code repr()})
	* <li>{@code %d} (convert an integer to its decimal representation)
	* </ul>
	* To encode a literal percent character, escape it as {@code %%}. It is an error to have a
	* non-escaped {@code %} at the end of the string or followed by any character not listed above.
	*
	* <p>If this printer has {@code simplifiedFormatStrings} set, only {@code %s} and {@code %%}
	* are permitted.
	*
	* @param pattern a format string that may contain placeholders
	* @param arguments an array containing arguments to substitute into the placeholders in order
	* @return the formatted string
	* @throws IllegalFormatException if {@code pattern} is not a valid format string, or if
	* {@code arguments} mismatches the number or type of placeholders in {@code pattern}
	*/
	@Override
	public BasePrinter format(String pattern, Object... arguments) {
	return this.formatWithList(pattern, Arrays.asList(arguments));
	}

	/**
	* Perform Python-style string formatting, similar to the {@code pattern % tuple} syntax.
	*
	* <p>Same as {@link #format(String, Object...)}, but with a list instead of variadic args.
	*/
	@Override
	public BasePrinter formatWithList(String pattern, List<?> arguments) {
	// TODO(bazel-team): support formatting arguments, and more complex Python patterns.
	// N.B. MissingFormatWidthException is the only kind of IllegalFormatException
	// whose constructor can take and display arbitrary error message, hence its use below.

	int length = pattern.length();
	int argLength = arguments.size();
	int i = 0; // index of next character in pattern
	int a = 0; // index of next argument in arguments

	while (i < length) {
	int p = pattern.indexOf('%', i);
	if (p == -1) {
	Printer.append(buffer, pattern, i, length);
	break;
	}
	if (p > i) {
	Printer.append(buffer, pattern, i, p);
	}
	if (p == length - 1) {
	throw new MissingFormatWidthException(
	"incomplete format pattern ends with %: " + this.repr(pattern));
	}
	char directive = pattern.charAt(p + 1);
	i = p + 2;
	switch (directive) {
	case '%':
	this.append('%');
	continue;
	case 'd':
	case 'r':
	case 's':
	if (simplifiedFormatStrings && (directive != 's')) {
	throw new UnknownFormatConversionException(
	"cannot use %" + directive + " substitution placeholder when "
	+ "simplifiedFormatStrings is set");
	}
	if (a >= argLength) {
	throw new MissingFormatWidthException(
	"not enough arguments for format pattern "
	+ Starlark.repr(pattern)
	+ ": "
	+ Starlark.repr(Tuple.copyOf(arguments)));
	}
	Object argument = arguments.get(a++);
	switch (directive) {
	case 'd':
	if (argument instanceof Integer) {
	this.append(argument.toString());
	continue;
	} else {
	throw new MissingFormatWidthException(
	"invalid argument " + Starlark.repr(argument) + " for format pattern %d");
	}
	case 'r':
	this.repr(argument);
	continue;
	case 's':
	this.str(argument);
	continue;
	}
	// fall through
	default:
	throw new MissingFormatWidthException(
	// The call to Starlark.repr doesn't cause an infinite recursion because it's
	// only used to format a string properly
	String.format(
	"unsupported format character \"%s\" at index %s in %s",
	String.valueOf(directive), p + 1, Starlark.repr(pattern)));
	}
	}
	if (a < argLength) {
	throw new MissingFormatWidthException(
	"not all arguments converted during string formatting");
	}
	return this;
	}

	@Override
	public BasePrinter append(char c) {
	Printer.append(buffer, c);
	return this;
	}

	@Override
	public BasePrinter append(CharSequence s) {
	Printer.append(buffer, s);
	return this;
	}

	BasePrinter append(CharSequence sequence, int start, int end) {
	return this.append(sequence.subSequence(start, end));
	}
	}

	/** A printer that breaks lines between 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) {

	// If the list is empty, do not split the presentation over
	// several lines.
	if (!list.iterator().hasNext()) {
	this.append(before + after);
	return this;
	}

	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;
	}
	}
	}