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

 // Copyright 2014 Google Inc. 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.auto.value.AutoValue;
 import com.google.common.base.Preconditions;
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.Interner;
 import com.google.common.collect.Interners;
 import com.google.common.collect.Lists;
 import com.google.devtools.build.lib.util.StringCanonicalizer;

 import java.io.Serializable;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.HashSet;
 import java.util.List;
 import java.util.Set;

 import javax.annotation.Nullable;

 /**
  * Function Signatures for BUILD language (same as Python)
  *
  * <p>Skylark's function signatures are just like Python3's.
  * A function may have 6 kinds of arguments:
  * positional mandatory, positional optional, positional rest (aka *star argument),
  * key-only mandatory, key-only optional, key rest (aka **star_star argument).
  * A caller may specify all arguments but the *star and **star_star arguments by name,
  * and thus all mandatory and optional arguments are named arguments.
  *
  * <p>To enable various optimizations in the argument processing routine,
  * we sort arguments according the following constraints, enabling corresponding optimizations:
  * <ol>
  * <li>The positional mandatories come just before the positional optionals,
  *   so they can be filled in one go.
  * <li>Positionals come first, so it's easy to prepend extra positional arguments such as "self"
  *   to an argument list, and we optimize for the common case of no key-only mandatory parameters.
  *   key-only parameters are thus grouped together.
  *   positional mandatory and key-only mandatory parameters are separate,
  *   but there no loop over a contiguous chunk of them, anyway.
  * <li>The named are all grouped together, with star and star_star rest arguments coming last.
  * <li>Mandatory arguments in each category (positional and named-only) come before the optional
  *   arguments, for the sake of slightly better clarity to human implementers. This eschews an
  *   optimization whereby grouping optionals together allows to iterate over them in one go instead
  *   of two; however, this relatively minor optimization only matters when keyword arguments are
  *   passed, at which point it is dwarfed by the slowness of keyword processing.
  * </ol>
  *
  * <p>Parameters are thus sorted in the following obvious order:
  * positional mandatory arguments (if any), positional optional arguments (if any),
  * key-only mandatory arguments (if any), key-only optional arguments (if any),
  * then star argument (if any), then star_star argument (if any).
  */
 @AutoValue
 public abstract class FunctionSignature implements Serializable {

   /**
    * The shape of a FunctionSignature, without names
    */
   @AutoValue
   public abstract static class Shape implements Serializable {
     private static final Interner<Shape> interner = Interners.newWeakInterner();

     /** Create a function signature */
     public static Shape create(
         int mandatoryPositionals,
         int optionalPositionals,
         int mandatoryNamedOnly,
         int optionalNamedOnly,
         boolean starArg,
         boolean kwArg) {
       Preconditions.checkArgument(
           0 <= mandatoryPositionals && 0 <= optionalPositionals
           && 0 <= mandatoryNamedOnly && 0 <= optionalNamedOnly);
       return interner.intern(new AutoValue_FunctionSignature_Shape(
           mandatoryPositionals, optionalPositionals,
           mandatoryNamedOnly, optionalNamedOnly, starArg, kwArg));
     }

     // These abstract getters specify the actual argument count fields to be defined by AutoValue.
     /** number of mandatory positional arguments */
     public abstract int getMandatoryPositionals();

     /** number of optional positional arguments */
     public abstract int getOptionalPositionals();

     /** number of mandatory named-only arguments. */
     public abstract int getMandatoryNamedOnly();

     /** number of optional named-only arguments */
     public abstract int getOptionalNamedOnly();

     /** indicator for presence of a star argument for extra positional arguments */
     public abstract boolean hasStarArg();

     /** indicator for presence of a star-star argument for extra keyword arguments */
     public abstract boolean hasKwArg();


     // The are computed argument counts
     /** number of optional positional arguments. */
     public int getPositionals() {
       return getMandatoryPositionals() + getOptionalPositionals();
     }

     /** number of optional named-only arguments. */
     public int getNamedOnly() {
       return getMandatoryNamedOnly() + getOptionalNamedOnly();
     }

     /** number of optional arguments. */
     public int getOptionals() {
       return getOptionalPositionals() + getOptionalNamedOnly();
     }

     /** total number of arguments */
     public int getArguments() {
       return getPositionals() + getNamedOnly() + (hasStarArg() ? 1 : 0) + (hasKwArg() ? 1 : 0);
     }
   }

   /**
    * Names of a FunctionSignature
    */
   private static Interner<ImmutableList<String>> namesInterner = Interners.newWeakInterner();

   /** Intern a list of names */
   public static ImmutableList<String> names(List<String> names) {
     return namesInterner.intern(ImmutableList.<String>copyOf(
         Lists.transform(names, StringCanonicalizer.INTERN)));
   }

   /** Intern a list of names */
   public static ImmutableList<String> names(String... names) {
     return names(ImmutableList.<String>copyOf(names));
   }

   // Interner
   private static Interner<FunctionSignature> signatureInterner = Interners.newWeakInterner();

   /**
    * Signatures proper.
    *
    * <p>A signature is a Shape and an ImmutableList of argument variable names
    * NB: we assume these lists are short, so we may do linear scans.
    */
   public static FunctionSignature create(Shape shape, ImmutableList<String> names) {
     Preconditions.checkArgument(names.size() == shape.getArguments());
     return signatureInterner.intern(new AutoValue_FunctionSignature(shape, names(names)));
   }


   // Field definition (details filled in by AutoValue)
   /** The shape */
   public abstract Shape getShape();

   /** The names */
   public abstract ImmutableList<String> getNames();

   /** append a representation of this signature to a string buffer. */
   public StringBuilder toStringBuilder(StringBuilder sb) {
     return WithValues.<Object, SkylarkType>create(this).toStringBuilder(sb);
   }

   @Override
   public String toString() {
     StringBuilder sb = new StringBuilder();
     toStringBuilder(sb);
     return sb.toString();
   }


   /**
    * FunctionSignature.WithValues: also specifies a List of default values and types.
    *
    * <p>The lists can be null, which is an optimized path for specifying all null values.
    *
    * <p>Note that if some values can be null (for BuiltinFunction, not for UserDefinedFunction),
    * you should use an ArrayList; otherwise, we recommend an ImmutableList.
    *
    * <p>V is the class of defaultValues and T is the class of types.
    * When parsing a function definition at compile-time, they are &lt;Expression, Expression&gt;;
    * when processing a @SkylarkSignature annotation at build-time, &lt;Object, SkylarkType&gt;.
    */
   @AutoValue
   public abstract static class WithValues<V, T> implements Serializable {

     // The fields
     /** The underlying signature with parameter shape and names */
     public abstract FunctionSignature getSignature();

     /** The default values (if any) as a List of one per optional parameter.
      * We might have preferred ImmutableList, but we care about
      * supporting null's for some BuiltinFunction's, and we don't spit on speed.
      */
     @Nullable public abstract List<V> getDefaultValues();

     /** The parameter types (if specified) as a List of one per parameter, including * and **.
      * We might have preferred ImmutableList, but we care about supporting null's
      * so we can take shortcut for untyped values.
      */
     @Nullable public abstract List<T> getTypes();


     /**
      * Create a signature with (default and type) values.
      * If you supply mutable List's, we trust that you won't modify them afterwards.
      */
     public static <V, T> WithValues<V, T> create(FunctionSignature signature,
         @Nullable List<V> defaultValues, @Nullable List<T> types) {
       Shape shape = signature.getShape();
       Preconditions.checkArgument(defaultValues == null
           || defaultValues.size() == shape.getOptionals());
       Preconditions.checkArgument(types == null
           || types.size() == shape.getArguments());
       return new AutoValue_FunctionSignature_WithValues<>(signature, defaultValues, types);
     }

     public static <V, T> WithValues<V, T> create(FunctionSignature signature,
         @Nullable List<V> defaultValues) {
       return create(signature, defaultValues, null);
     }

     public static <V, T> WithValues<V, T> create(FunctionSignature signature,
         @Nullable V[] defaultValues) {
       return create(signature, Arrays.asList(defaultValues), null);
     }

     public static <V, T> WithValues<V, T> create(FunctionSignature signature) {
       return create(signature, null, null);
     }

     /**
      * Parse a list of Parameter into a FunctionSignature.
      *
      * <p>To be used both by the Parser and by the SkylarkSignature annotation processor.
      */
     public static <V, T> WithValues<V, T> of(Iterable<Parameter<V, T>> parameters)
         throws SignatureException {
       int mandatoryPositionals = 0;
       int optionalPositionals = 0;
       int mandatoryNamedOnly = 0;
       int optionalNamedOnly = 0;
       boolean hasStarStar = false;
       boolean hasStar = false;
       @Nullable String star = null;
       @Nullable String starStar = null;
       @Nullable T starType = null;
       @Nullable T starStarType = null;
       ArrayList<String> params = new ArrayList<>();
       ArrayList<V> defaults = new ArrayList<>();
       ArrayList<T> types = new ArrayList<>();
       // optional named-only parameters are kept aside to be spliced after the mandatory ones.
       ArrayList<String> optionalNamedOnlyParams = new ArrayList<>();
       ArrayList<T> optionalNamedOnlyTypes = new ArrayList<>();
       ArrayList<V> optionalNamedOnlyDefaultValues = new ArrayList<>();
       boolean defaultRequired = false; // true after mandatory positionals and before star.
       Set<String> paramNameSet = new HashSet<>(); // set of names, to avoid duplicates

       for (Parameter<V, T> param : parameters) {
         if (hasStarStar) {
           throw new SignatureException("illegal parameter after star-star parameter", param);
         }
         @Nullable String name = param.getName();
         @Nullable T type = param.getType();
         if (param.hasName()) {
           if (paramNameSet.contains(name)) {
             throw new SignatureException("duplicate parameter name in function definition", param);
           }
           paramNameSet.add(name);
         }
         if (param.isStarStar()) {
           hasStarStar = true;
           starStar = name;
           starStarType = type;
         } else if (param.isStar()) {
           if (hasStar) {
             throw new SignatureException(
                 "duplicate star parameter in function definition", param);
           }
           hasStar = true;
           defaultRequired = false;
           if (param.hasName()) {
             star = name;
             starType = type;
           }
         } else if (hasStar && param.isOptional()) {
           optionalNamedOnly++;
           optionalNamedOnlyParams.add(name);
           optionalNamedOnlyTypes.add(type);
           optionalNamedOnlyDefaultValues.add(param.getDefaultValue());
         } else {
           params.add(name);
           types.add(type);
           if (param.isOptional()) {
             optionalPositionals++;
             defaults.add(param.getDefaultValue());
             defaultRequired = true;
           } else if (hasStar) {
             mandatoryNamedOnly++;
           } else if (defaultRequired) {
               throw new SignatureException(
                   "a mandatory positional parameter must not follow an optional parameter",
                   param);
           } else {
             mandatoryPositionals++;
           }
         }
       }
       params.addAll(optionalNamedOnlyParams);
       types.addAll(optionalNamedOnlyTypes);
       defaults.addAll(optionalNamedOnlyDefaultValues);

       if (star != null) {
         params.add(star);
         types.add(starType);
       }
       if (starStar != null) {
         params.add(starStar);
         types.add(starStarType);
       }
       return WithValues.<V, T>create(
           FunctionSignature.create(
               Shape.create(
                   mandatoryPositionals, optionalPositionals,
                   mandatoryNamedOnly, optionalNamedOnly,
                   star != null, starStar != null),
               ImmutableList.<String>copyOf(params)),
           FunctionSignature.<V>valueListOrNull(defaults),
           FunctionSignature.<T>valueListOrNull(types));
     }

     public StringBuilder toStringBuilder(final StringBuilder sb) {
       return toStringBuilder(sb, true, true, true, false);
     }

     /**
      * Appends a representation of this signature to a string buffer.
      * @param sb Output StringBuffer
      * @param showNames Determines whether the names of arguments should be printed
      * @param showDefaults Determines whether the default values of arguments should be printed (if
      * present)
      * @param skipMissingTypeNames Determines whether missing type names should be omitted (true) or
      * replaced with "object" (false). If showNames is false, "object" is always used as a type name
      * to prevent blank spaces.
      * @param skipFirstMandatory Determines whether the first mandatory parameter should be omitted.
      */
     public StringBuilder toStringBuilder(final StringBuilder sb, final boolean showNames,
         final boolean showDefaults, final boolean skipMissingTypeNames,
         final boolean skipFirstMandatory) {
       FunctionSignature signature = getSignature();
       Shape shape = signature.getShape();
       final ImmutableList<String> names = signature.getNames();
       @Nullable final List<V> defaultValues = getDefaultValues();
       @Nullable final List<T> types = getTypes();

       int mandatoryPositionals = shape.getMandatoryPositionals();
       int optionalPositionals = shape.getOptionalPositionals();
       int mandatoryNamedOnly = shape.getMandatoryNamedOnly();
       int optionalNamedOnly = shape.getOptionalNamedOnly();
       boolean starArg = shape.hasStarArg();
       boolean kwArg = shape.hasKwArg();
       int positionals = mandatoryPositionals + optionalPositionals;
       int namedOnly = mandatoryNamedOnly + optionalNamedOnly;
       int named = positionals + namedOnly;
       int args = named + (starArg ? 1 : 0) + (kwArg ? 1 : 0);
       int endMandatoryNamedOnly = positionals + mandatoryNamedOnly;
       boolean hasStar = starArg || (namedOnly > 0);
       int iStarArg = named;
       int iKwArg = args - 1;

       class Show {
         private boolean isMore = false;
         private int j = 0;

         public void comma() {
           if (isMore) { sb.append(", "); }
           isMore = true;
         }
         public void type(int i) {
           // We have to assign an artificial type string when the type is null.
           // This happens when either
           // a) there is no type defined (such as in user-defined functions) or
           // b) the type is java.lang.Object.
           boolean noTypeDefined = (types == null || types.get(i) == null);
           String typeString = noTypeDefined ? "object" : types.get(i).toString();
           if (noTypeDefined && showNames && skipMissingTypeNames) {
             // This is the only case where we don't want to append typeString.
             // If showNames = false, we ignore skipMissingTypeNames = true and append "object"
             // in order to prevent blank spaces.
           } else {
             // We only append colons when there is a name.
             if (showNames) {
               sb.append(": ");
             }
             sb.append(typeString);
           }
         }
         public void mandatory(int i) {
           comma();
           if (showNames) {
             sb.append(names.get(i));
           }
           type(i);
         }
         public void optional(int i) {
           mandatory(i);
           if (showDefaults) {
             sb.append(" = ");
             if (defaultValues == null) {
               sb.append("?");
             } else {
               Printer.write(sb, defaultValues.get(j++));
             }
           }
         }
       };
       Show show = new Show();

       int i = skipFirstMandatory ? 1 : 0;
       for (; i < mandatoryPositionals; i++) {
         show.mandatory(i);
       }
       for (; i < positionals; i++) {
         show.optional(i);
       }
       if (hasStar) {
         show.comma();
         sb.append("*");
         if (starArg && showNames) {
           sb.append(names.get(iStarArg));
         }
       }
       for (; i < endMandatoryNamedOnly; i++) {
         show.mandatory(i);
       }
       for (; i < named; i++) {
         show.optional(i);
       }
       if (kwArg) {
         show.comma();
         sb.append("**");
         if (showNames) {
           sb.append(names.get(iKwArg));
         }
       }

       return sb;
     }

     @Override
     public String toString() {
       StringBuilder sb = new StringBuilder();
       toStringBuilder(sb);
       return sb.toString();
     }
   }

   /** The given List, or null if all the list elements are null. */
   @Nullable public static <E> List<E> valueListOrNull(List<E> list) {
     if (list == null) {
       return null;
     }
     for (E value : list) {
       if (value != null) {
         return list;
       }
     }
     return null;
   }

   /**
    * Constructs a function signature (with names) from signature description and names.
    * This method covers the general case.
    * The number of optional named-only parameters is deduced from the other arguments.
    *
    * @param numMandatoryPositionals an int for the number of mandatory positional parameters
    * @param numOptionalPositionals an int for the number of optional positional parameters
    * @param numMandatoryNamedOnly an int for the number of mandatory named-only parameters
    * @param starArg a boolean for whether there is a starred parameter
    * @param kwArg a boolean for whether there is a star-starred parameter
    * @param names an Array of String for the parameter names
    * @return a FunctionSignature
    */
   public static FunctionSignature of(int numMandatoryPositionals, int numOptionalPositionals,
       int numMandatoryNamedOnly, boolean starArg, boolean kwArg, String... names) {
     return create(Shape.create(
         numMandatoryPositionals,
         numOptionalPositionals,
         numMandatoryNamedOnly,
         names.length - (kwArg ? 1 : 0) - (starArg ? 1 : 0)
             - numMandatoryPositionals - numOptionalPositionals - numMandatoryNamedOnly,
         starArg, kwArg),
         ImmutableList.<String>copyOf(names));
   }

   /**
    * Constructs a function signature from mandatory positional argument names.
    *
    * @param names an Array of String for the positional parameter names
    * @return a FunctionSignature
    */
   public static FunctionSignature of(String... names) {
     return of(names.length, 0, 0, false, false, names);
   }

   /**
    * Constructs a function signature from positional argument names.
    *
    * @param numMandatory an int for the number of mandatory positional parameters
    * @param names an Array of String for the positional parameter names
    * @return a FunctionSignature
    */
   public static FunctionSignature of(int numMandatory, String... names) {
     return of(numMandatory, names.length - numMandatory, 0, false, false, names);
   }

   /**
    * Constructs a function signature from mandatory named-only argument names.
    *
    * @param names an Array of String for the mandatory named-only parameter names
    * @return a FunctionSignature
    */
   public static FunctionSignature namedOnly(String... names) {
     return of(0, 0, names.length, false, false, names);
   }

   /**
    * Constructs a function signature from named-only argument names.
    *
    * @param numMandatory an int for the number of mandatory named-only parameters
    * @param names an Array of String for the named-only parameter names
    * @return a FunctionSignature
    */
   public static FunctionSignature namedOnly(int numMandatory, String... names) {
     return of(0, 0, numMandatory, false, false, names);
   }

   /** Invalid signature from Parser or from SkylarkSignature annotations */
   protected static class SignatureException extends Exception {
     @Nullable private final Parameter<?, ?> parameter;

     /** SignatureException from a message and a Parameter */
     public SignatureException(String message, @Nullable Parameter<?, ?> parameter) {
       super(message);
       this.parameter = parameter;
     }

     /** what parameter caused the exception, if identified? */
     @Nullable public Parameter<?, ?> getParameter() {
       return parameter;
     }
   }

   /** A ready-made signature to allow only keyword arguments and put them in a kwarg parameter */
   public static final FunctionSignature KWARGS =
       FunctionSignature.of(0, 0, 0, false, true, "kwargs");
 }
	// Copyright 2014 Google Inc. 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.auto.value.AutoValue;
	import com.google.common.base.Preconditions;
	import com.google.common.collect.ImmutableList;
	import com.google.common.collect.Interner;
	import com.google.common.collect.Interners;
	import com.google.common.collect.Lists;
	import com.google.devtools.build.lib.util.StringCanonicalizer;

	import java.io.Serializable;
	import java.util.ArrayList;
	import java.util.Arrays;
	import java.util.HashSet;
	import java.util.List;
	import java.util.Set;

	import javax.annotation.Nullable;

	/**
	* Function Signatures for BUILD language (same as Python)
	*
	* <p>Skylark's function signatures are just like Python3's.
	* A function may have 6 kinds of arguments:
	* positional mandatory, positional optional, positional rest (aka *star argument),
	* key-only mandatory, key-only optional, key rest (aka **star_star argument).
	* A caller may specify all arguments but the star and *star_star arguments by name,
	* and thus all mandatory and optional arguments are named arguments.
	*
	* <p>To enable various optimizations in the argument processing routine,
	* we sort arguments according the following constraints, enabling corresponding optimizations:
	* <ol>
	* <li>The positional mandatories come just before the positional optionals,
	* so they can be filled in one go.
	* <li>Positionals come first, so it's easy to prepend extra positional arguments such as "self"
	* to an argument list, and we optimize for the common case of no key-only mandatory parameters.
	* key-only parameters are thus grouped together.
	* positional mandatory and key-only mandatory parameters are separate,
	* but there no loop over a contiguous chunk of them, anyway.
	* <li>The named are all grouped together, with star and star_star rest arguments coming last.
	* <li>Mandatory arguments in each category (positional and named-only) come before the optional
	* arguments, for the sake of slightly better clarity to human implementers. This eschews an
	* optimization whereby grouping optionals together allows to iterate over them in one go instead
	* of two; however, this relatively minor optimization only matters when keyword arguments are
	* passed, at which point it is dwarfed by the slowness of keyword processing.
	* </ol>
	*
	* <p>Parameters are thus sorted in the following obvious order:
	* positional mandatory arguments (if any), positional optional arguments (if any),
	* key-only mandatory arguments (if any), key-only optional arguments (if any),
	* then star argument (if any), then star_star argument (if any).
	*/
	@AutoValue
	public abstract class FunctionSignature implements Serializable {

	/**
	* The shape of a FunctionSignature, without names
	*/
	@AutoValue
	public abstract static class Shape implements Serializable {
	private static final Interner<Shape> interner = Interners.newWeakInterner();

	/** Create a function signature */
	public static Shape create(
	int mandatoryPositionals,
	int optionalPositionals,
	int mandatoryNamedOnly,
	int optionalNamedOnly,
	boolean starArg,
	boolean kwArg) {
	Preconditions.checkArgument(
	0 <= mandatoryPositionals && 0 <= optionalPositionals
	&& 0 <= mandatoryNamedOnly && 0 <= optionalNamedOnly);
	return interner.intern(new AutoValue_FunctionSignature_Shape(
	mandatoryPositionals, optionalPositionals,
	mandatoryNamedOnly, optionalNamedOnly, starArg, kwArg));
	}

	// These abstract getters specify the actual argument count fields to be defined by AutoValue.
	/** number of mandatory positional arguments */
	public abstract int getMandatoryPositionals();

	/** number of optional positional arguments */
	public abstract int getOptionalPositionals();

	/** number of mandatory named-only arguments. */
	public abstract int getMandatoryNamedOnly();

	/** number of optional named-only arguments */
	public abstract int getOptionalNamedOnly();

	/** indicator for presence of a star argument for extra positional arguments */
	public abstract boolean hasStarArg();

	/** indicator for presence of a star-star argument for extra keyword arguments */
	public abstract boolean hasKwArg();


	// The are computed argument counts
	/** number of optional positional arguments. */
	public int getPositionals() {
	return getMandatoryPositionals() + getOptionalPositionals();
	}

	/** number of optional named-only arguments. */
	public int getNamedOnly() {
	return getMandatoryNamedOnly() + getOptionalNamedOnly();
	}

	/** number of optional arguments. */
	public int getOptionals() {
	return getOptionalPositionals() + getOptionalNamedOnly();
	}

	/** total number of arguments */
	public int getArguments() {
	return getPositionals() + getNamedOnly() + (hasStarArg() ? 1 : 0) + (hasKwArg() ? 1 : 0);
	}
	}

	/**
	* Names of a FunctionSignature
	*/
	private static Interner<ImmutableList<String>> namesInterner = Interners.newWeakInterner();

	/** Intern a list of names */
	public static ImmutableList<String> names(List<String> names) {
	return namesInterner.intern(ImmutableList.<String>copyOf(
	Lists.transform(names, StringCanonicalizer.INTERN)));
	}

	/** Intern a list of names */
	public static ImmutableList<String> names(String... names) {
	return names(ImmutableList.<String>copyOf(names));
	}

	// Interner
	private static Interner<FunctionSignature> signatureInterner = Interners.newWeakInterner();

	/**
	* Signatures proper.
	*
	* <p>A signature is a Shape and an ImmutableList of argument variable names
	* NB: we assume these lists are short, so we may do linear scans.
	*/
	public static FunctionSignature create(Shape shape, ImmutableList<String> names) {
	Preconditions.checkArgument(names.size() == shape.getArguments());
	return signatureInterner.intern(new AutoValue_FunctionSignature(shape, names(names)));
	}



	// Field definition (details filled in by AutoValue)
	/** The shape */
	public abstract Shape getShape();

	/** The names */
	public abstract ImmutableList<String> getNames();

	/** append a representation of this signature to a string buffer. */
	public StringBuilder toStringBuilder(StringBuilder sb) {
	return WithValues.<Object, SkylarkType>create(this).toStringBuilder(sb);
	}

	@Override
	public String toString() {
	StringBuilder sb = new StringBuilder();
	toStringBuilder(sb);
	return sb.toString();
	}


	/**
	* FunctionSignature.WithValues: also specifies a List of default values and types.
	*
	* <p>The lists can be null, which is an optimized path for specifying all null values.
	*
	* <p>Note that if some values can be null (for BuiltinFunction, not for UserDefinedFunction),
	* you should use an ArrayList; otherwise, we recommend an ImmutableList.
	*
	* <p>V is the class of defaultValues and T is the class of types.
	* When parsing a function definition at compile-time, they are <Expression, Expression>;
	* when processing a @SkylarkSignature annotation at build-time, <Object, SkylarkType>.
	*/
	@AutoValue
	public abstract static class WithValues<V, T> implements Serializable {

	// The fields
	/** The underlying signature with parameter shape and names */
	public abstract FunctionSignature getSignature();

	/** The default values (if any) as a List of one per optional parameter.
	* We might have preferred ImmutableList, but we care about
	* supporting null's for some BuiltinFunction's, and we don't spit on speed.
	*/
	@Nullable public abstract List<V> getDefaultValues();

	/** The parameter types (if specified) as a List of one per parameter, including * and **.
	* We might have preferred ImmutableList, but we care about supporting null's
	* so we can take shortcut for untyped values.
	*/
	@Nullable public abstract List<T> getTypes();


	/**
	* Create a signature with (default and type) values.
	* If you supply mutable List's, we trust that you won't modify them afterwards.
	*/
	public static <V, T> WithValues<V, T> create(FunctionSignature signature,
	@Nullable List<V> defaultValues, @Nullable List<T> types) {
	Shape shape = signature.getShape();
	Preconditions.checkArgument(defaultValues == null
	\|\| defaultValues.size() == shape.getOptionals());
	Preconditions.checkArgument(types == null
	\|\| types.size() == shape.getArguments());
	return new AutoValue_FunctionSignature_WithValues<>(signature, defaultValues, types);
	}

	public static <V, T> WithValues<V, T> create(FunctionSignature signature,
	@Nullable List<V> defaultValues) {
	return create(signature, defaultValues, null);
	}

	public static <V, T> WithValues<V, T> create(FunctionSignature signature,
	@Nullable V[] defaultValues) {
	return create(signature, Arrays.asList(defaultValues), null);
	}

	public static <V, T> WithValues<V, T> create(FunctionSignature signature) {
	return create(signature, null, null);
	}

	/**
	* Parse a list of Parameter into a FunctionSignature.
	*
	* <p>To be used both by the Parser and by the SkylarkSignature annotation processor.
	*/
	public static <V, T> WithValues<V, T> of(Iterable<Parameter<V, T>> parameters)
	throws SignatureException {
	int mandatoryPositionals = 0;
	int optionalPositionals = 0;
	int mandatoryNamedOnly = 0;
	int optionalNamedOnly = 0;
	boolean hasStarStar = false;
	boolean hasStar = false;
	@Nullable String star = null;
	@Nullable String starStar = null;
	@Nullable T starType = null;
	@Nullable T starStarType = null;
	ArrayList<String> params = new ArrayList<>();
	ArrayList<V> defaults = new ArrayList<>();
	ArrayList<T> types = new ArrayList<>();
	// optional named-only parameters are kept aside to be spliced after the mandatory ones.
	ArrayList<String> optionalNamedOnlyParams = new ArrayList<>();
	ArrayList<T> optionalNamedOnlyTypes = new ArrayList<>();
	ArrayList<V> optionalNamedOnlyDefaultValues = new ArrayList<>();
	boolean defaultRequired = false; // true after mandatory positionals and before star.
	Set<String> paramNameSet = new HashSet<>(); // set of names, to avoid duplicates

	for (Parameter<V, T> param : parameters) {
	if (hasStarStar) {
	throw new SignatureException("illegal parameter after star-star parameter", param);
	}
	@Nullable String name = param.getName();
	@Nullable T type = param.getType();
	if (param.hasName()) {
	if (paramNameSet.contains(name)) {
	throw new SignatureException("duplicate parameter name in function definition", param);
	}
	paramNameSet.add(name);
	}
	if (param.isStarStar()) {
	hasStarStar = true;
	starStar = name;
	starStarType = type;
	} else if (param.isStar()) {
	if (hasStar) {
	throw new SignatureException(
	"duplicate star parameter in function definition", param);
	}
	hasStar = true;
	defaultRequired = false;
	if (param.hasName()) {
	star = name;
	starType = type;
	}
	} else if (hasStar && param.isOptional()) {
	optionalNamedOnly++;
	optionalNamedOnlyParams.add(name);
	optionalNamedOnlyTypes.add(type);
	optionalNamedOnlyDefaultValues.add(param.getDefaultValue());
	} else {
	params.add(name);
	types.add(type);
	if (param.isOptional()) {
	optionalPositionals++;
	defaults.add(param.getDefaultValue());
	defaultRequired = true;
	} else if (hasStar) {
	mandatoryNamedOnly++;
	} else if (defaultRequired) {
	throw new SignatureException(
	"a mandatory positional parameter must not follow an optional parameter",
	param);
	} else {
	mandatoryPositionals++;
	}
	}
	}
	params.addAll(optionalNamedOnlyParams);
	types.addAll(optionalNamedOnlyTypes);
	defaults.addAll(optionalNamedOnlyDefaultValues);

	if (star != null) {
	params.add(star);
	types.add(starType);
	}
	if (starStar != null) {
	params.add(starStar);
	types.add(starStarType);
	}
	return WithValues.<V, T>create(
	FunctionSignature.create(
	Shape.create(
	mandatoryPositionals, optionalPositionals,
	mandatoryNamedOnly, optionalNamedOnly,
	star != null, starStar != null),
	ImmutableList.<String>copyOf(params)),
	FunctionSignature.<V>valueListOrNull(defaults),
	FunctionSignature.<T>valueListOrNull(types));
	}

	public StringBuilder toStringBuilder(final StringBuilder sb) {
	return toStringBuilder(sb, true, true, true, false);
	}

	/**
	* Appends a representation of this signature to a string buffer.
	* @param sb Output StringBuffer
	* @param showNames Determines whether the names of arguments should be printed
	* @param showDefaults Determines whether the default values of arguments should be printed (if
	* present)
	* @param skipMissingTypeNames Determines whether missing type names should be omitted (true) or
	* replaced with "object" (false). If showNames is false, "object" is always used as a type name
	* to prevent blank spaces.
	* @param skipFirstMandatory Determines whether the first mandatory parameter should be omitted.
	*/
	public StringBuilder toStringBuilder(final StringBuilder sb, final boolean showNames,
	final boolean showDefaults, final boolean skipMissingTypeNames,
	final boolean skipFirstMandatory) {
	FunctionSignature signature = getSignature();
	Shape shape = signature.getShape();
	final ImmutableList<String> names = signature.getNames();
	@Nullable final List<V> defaultValues = getDefaultValues();
	@Nullable final List<T> types = getTypes();

	int mandatoryPositionals = shape.getMandatoryPositionals();
	int optionalPositionals = shape.getOptionalPositionals();
	int mandatoryNamedOnly = shape.getMandatoryNamedOnly();
	int optionalNamedOnly = shape.getOptionalNamedOnly();
	boolean starArg = shape.hasStarArg();
	boolean kwArg = shape.hasKwArg();
	int positionals = mandatoryPositionals + optionalPositionals;
	int namedOnly = mandatoryNamedOnly + optionalNamedOnly;
	int named = positionals + namedOnly;
	int args = named + (starArg ? 1 : 0) + (kwArg ? 1 : 0);
	int endMandatoryNamedOnly = positionals + mandatoryNamedOnly;
	boolean hasStar = starArg \|\| (namedOnly > 0);
	int iStarArg = named;
	int iKwArg = args - 1;

	class Show {
	private boolean isMore = false;
	private int j = 0;

	public void comma() {
	if (isMore) { sb.append(", "); }
	isMore = true;
	}
	public void type(int i) {
	// We have to assign an artificial type string when the type is null.
	// This happens when either
	// a) there is no type defined (such as in user-defined functions) or
	// b) the type is java.lang.Object.
	boolean noTypeDefined = (types == null \|\| types.get(i) == null);
	String typeString = noTypeDefined ? "object" : types.get(i).toString();
	if (noTypeDefined && showNames && skipMissingTypeNames) {
	// This is the only case where we don't want to append typeString.
	// If showNames = false, we ignore skipMissingTypeNames = true and append "object"
	// in order to prevent blank spaces.
	} else {
	// We only append colons when there is a name.
	if (showNames) {
	sb.append(": ");
	}
	sb.append(typeString);
	}
	}
	public void mandatory(int i) {
	comma();
	if (showNames) {
	sb.append(names.get(i));
	}
	type(i);
	}
	public void optional(int i) {
	mandatory(i);
	if (showDefaults) {
	sb.append(" = ");
	if (defaultValues == null) {
	sb.append("?");
	} else {
	Printer.write(sb, defaultValues.get(j++));
	}
	}
	}
	};
	Show show = new Show();

	int i = skipFirstMandatory ? 1 : 0;
	for (; i < mandatoryPositionals; i++) {
	show.mandatory(i);
	}
	for (; i < positionals; i++) {
	show.optional(i);
	}
	if (hasStar) {
	show.comma();
	sb.append("*");
	if (starArg && showNames) {
	sb.append(names.get(iStarArg));
	}
	}
	for (; i < endMandatoryNamedOnly; i++) {
	show.mandatory(i);
	}
	for (; i < named; i++) {
	show.optional(i);
	}
	if (kwArg) {
	show.comma();
	sb.append("**");
	if (showNames) {
	sb.append(names.get(iKwArg));
	}
	}

	return sb;
	}

	@Override
	public String toString() {
	StringBuilder sb = new StringBuilder();
	toStringBuilder(sb);
	return sb.toString();
	}
	}

	/** The given List, or null if all the list elements are null. */
	@Nullable public static <E> List<E> valueListOrNull(List<E> list) {
	if (list == null) {
	return null;
	}
	for (E value : list) {
	if (value != null) {
	return list;
	}
	}
	return null;
	}

	/**
	* Constructs a function signature (with names) from signature description and names.
	* This method covers the general case.
	* The number of optional named-only parameters is deduced from the other arguments.
	*
	* @param numMandatoryPositionals an int for the number of mandatory positional parameters
	* @param numOptionalPositionals an int for the number of optional positional parameters
	* @param numMandatoryNamedOnly an int for the number of mandatory named-only parameters
	* @param starArg a boolean for whether there is a starred parameter
	* @param kwArg a boolean for whether there is a star-starred parameter
	* @param names an Array of String for the parameter names
	* @return a FunctionSignature
	*/
	public static FunctionSignature of(int numMandatoryPositionals, int numOptionalPositionals,
	int numMandatoryNamedOnly, boolean starArg, boolean kwArg, String... names) {
	return create(Shape.create(
	numMandatoryPositionals,
	numOptionalPositionals,
	numMandatoryNamedOnly,
	names.length - (kwArg ? 1 : 0) - (starArg ? 1 : 0)
	- numMandatoryPositionals - numOptionalPositionals - numMandatoryNamedOnly,
	starArg, kwArg),
	ImmutableList.<String>copyOf(names));
	}

	/**
	* Constructs a function signature from mandatory positional argument names.
	*
	* @param names an Array of String for the positional parameter names
	* @return a FunctionSignature
	*/
	public static FunctionSignature of(String... names) {
	return of(names.length, 0, 0, false, false, names);
	}

	/**
	* Constructs a function signature from positional argument names.
	*
	* @param numMandatory an int for the number of mandatory positional parameters
	* @param names an Array of String for the positional parameter names
	* @return a FunctionSignature
	*/
	public static FunctionSignature of(int numMandatory, String... names) {
	return of(numMandatory, names.length - numMandatory, 0, false, false, names);
	}

	/**
	* Constructs a function signature from mandatory named-only argument names.
	*
	* @param names an Array of String for the mandatory named-only parameter names
	* @return a FunctionSignature
	*/
	public static FunctionSignature namedOnly(String... names) {
	return of(0, 0, names.length, false, false, names);
	}

	/**
	* Constructs a function signature from named-only argument names.
	*
	* @param numMandatory an int for the number of mandatory named-only parameters
	* @param names an Array of String for the named-only parameter names
	* @return a FunctionSignature
	*/
	public static FunctionSignature namedOnly(int numMandatory, String... names) {
	return of(0, 0, numMandatory, false, false, names);
	}

	/** Invalid signature from Parser or from SkylarkSignature annotations */
	protected static class SignatureException extends Exception {
	@Nullable private final Parameter<?, ?> parameter;

	/** SignatureException from a message and a Parameter */
	public SignatureException(String message, @Nullable Parameter<?, ?> parameter) {
	super(message);
	this.parameter = parameter;
	}

	/** what parameter caused the exception, if identified? */
	@Nullable public Parameter<?, ?> getParameter() {
	return parameter;
	}
	}

	/** A ready-made signature to allow only keyword arguments and put them in a kwarg parameter */
	public static final FunctionSignature KWARGS =
	FunctionSignature.of(0, 0, 0, false, true, "kwargs");
	}