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

 // Copyright 2014 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 static com.google.common.collect.ImmutableList.toImmutableList;

 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.devtools.build.lib.concurrent.BlazeInterners;
 import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
 import com.google.devtools.build.lib.syntax.Printer.BasePrinter;
 import com.google.devtools.build.lib.util.StringCanonicalizer;
 import java.util.ArrayList;
 import java.util.Collections;
 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>Starlark's function signatures are just like Python3's. A function may have 6 kinds of
  * parameters: positional mandatory, positional optional, positional rest (aka *args or variadic
  * parameter), keyword-only mandatory, keyword-only optional, keyword rest (aka **kwargs parameter).
  * A caller may specify all arguments but the *args and **kwargs arguments by name, and thus all
  * mandatory and optional parameters are named parameters.
  *
  * <p>To enable various optimizations in the argument processing routine, we sort parameters
  * 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 is no loop over a contiguous chunk of
  *       them, anyway.
  *   <li>The named are all grouped together, with star and star_star rest parameters coming last.
  *   <li>Mandatory parameters in each category (positional and named-only) come before the optional
  *       parameters, 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 order: positional mandatory parameters (if any),
  * positional optional parameters (if any), key-only mandatory parameters (if any), key-only
  * optional parameters (if any), then star parameter (if any), then star_star parameter (if any).
  */
 @AutoCodec
 @AutoValue
 public abstract class FunctionSignature {

   // These abstract getters specify the actual parameter count fields to be defined by AutoValue.

   /** Number of mandatory positional parameters */
   public abstract int numMandatoryPositionals();

   /** Number of optional positional parameters */
   public abstract int numOptionalPositionals();

   /** Number of mandatory named-only parameters. */
   public abstract int numMandatoryNamedOnly();

   /** Number of optional named-only parameters */
   public abstract int numOptionalNamedOnly();

   /** True if function has variadic parameter, {@code def f(*args)}. */
   public abstract boolean hasVarargs();

   /** True if function has residual keyword-argument parameter, {@code def f(**kwargs)}. */
   public abstract boolean hasKwargs();

   /** Parameter names. */
   public abstract ImmutableList<String> getParameterNames();

   // computed parameter counts

   /** Number of optional and mandatory positional parameters. */
   public int numPositionals() {
     return numMandatoryPositionals() + numOptionalPositionals();
   }

   /** Number of optional and mandatory named-only parameters. */
   public int numNamedOnly() {
     return numMandatoryNamedOnly() + numOptionalNamedOnly();
   }

   /** number of optional parameters. */
   public int numOptionals() {
     return numOptionalPositionals() + numOptionalNamedOnly();
   }

   /** number of all named parameters: mandatory and optional of positionals and named-only */
   public int numAllNamed() {
     return numPositionals() + numNamedOnly();
   }

   /** total number of parameters */
   public int numParameters() {
     return numAllNamed() + (hasVarargs() ? 1 : 0) + (hasKwargs() ? 1 : 0);
   }

   private static final Interner<ImmutableList<String>> namesInterner =
       BlazeInterners.newWeakInterner();

   /** Intern a list of names. */
   private static ImmutableList<String> names(List<String> names) {
     return namesInterner.intern(
         names.stream().map(StringCanonicalizer::intern).collect(toImmutableList()));
   }

   // Interner.
   // Are there really a significant number of duplicates? Why??
   private static final Interner<FunctionSignature> signatureInterner =
       BlazeInterners.newWeakInterner();

   // TODO(adonovan): not a user-friendly API. Provide external callers with this function:
   //   FunctionSignature.parse("a, b=1, *, c, d=2, *args, **kwargs")
   // implemented by invoking the Starlark parser. (Most uses are in tests.)
   @AutoCodec.Instantiator
   public static FunctionSignature create(
       int numMandatoryPositionals,
       int numOptionalPositionals,
       int numMandatoryNamedOnly,
       int numOptionalNamedOnly,
       boolean hasVarargs,
       boolean hasKwargs,
       ImmutableList<String> parameterNames) {
     Preconditions.checkArgument(
         0 <= numMandatoryPositionals
             && 0 <= numOptionalPositionals
             && 0 <= numMandatoryNamedOnly
             && 0 <= numOptionalNamedOnly);

     FunctionSignature sig =
         new AutoValue_FunctionSignature(
             numMandatoryPositionals,
             numOptionalPositionals,
             numMandatoryNamedOnly,
             numOptionalNamedOnly,
             hasVarargs,
             hasKwargs,
             names(parameterNames));

     Preconditions.checkArgument(parameterNames.size() == sig.numParameters());
     return signatureInterner.intern(sig);
   }

   /** 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 StarlarkFunction), 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;.
    */
   @AutoCodec
   @AutoValue
   public abstract static class WithValues<V, T> {

     /** the underlying parameter signature */
     public abstract FunctionSignature getSignature();

     /**
      * The default values (if any) as an unmodifiable List of one per optional parameter. May
      * contain nulls.
      */
     @Nullable public abstract List<V> getDefaultValues();

     /**
      * The parameter types (if specified) as an unmodifiable List of one per parameter, including *
      * and **. May contain nulls.
      */
     @Nullable public abstract List<T> getTypes();

     /** Create a signature with (default and type) values. */
     public static <V, T> WithValues<V, T> create(FunctionSignature signature,
         @Nullable List<V> defaultValues, @Nullable List<T> types) {
       List<V> convertedDefaultValues = null;
       if (defaultValues != null) {
         Preconditions.checkArgument(defaultValues.size() == signature.numOptionals());
         List<V> copiedDefaultValues = new ArrayList<>();
         copiedDefaultValues.addAll(defaultValues);
         convertedDefaultValues = Collections.unmodifiableList(copiedDefaultValues);
       }
       List<T> convertedTypes = null;
       if (types != null) {
         Preconditions.checkArgument(types.size() == signature.numParameters());
         List<T> copiedTypes = new ArrayList<>();
         copiedTypes.addAll(types);
         convertedTypes = Collections.unmodifiableList(copiedTypes);
       }
       return createInternal(signature, convertedDefaultValues, convertedTypes);
     }

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

     @AutoCodec.VisibleForSerialization
     @AutoCodec.Instantiator
     static <V, T> WithValues<V, T> createInternal(
         FunctionSignature signature, @Nullable List<V> defaultValues, @Nullable List<T> types) {
       return new AutoValue_FunctionSignature_WithValues<>(signature, defaultValues, types);
     }

     /** Convert a list of Parameter into a FunctionSignature. */
     // TODO(adonovan): inline into parser (or validator) and simplify.
     static WithValues<Expression, Expression> fromParameters(Iterable<Parameter> 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;
       ArrayList<String> params = new ArrayList<>();
       ArrayList<Expression> defaults = new ArrayList<>();
       // optional named-only parameters are kept aside to be spliced after the mandatory ones.
       ArrayList<String> optionalNamedOnlyParams = new ArrayList<>();
       ArrayList<Expression> 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 param : parameters) {
         if (hasStarStar) {
           throw new SignatureException("illegal parameter after star-star parameter", param);
         }
         @Nullable String name = param.getName();
         if (param.getName() != null) {
           if (paramNameSet.contains(name)) {
             throw new SignatureException("duplicate parameter name in function definition", param);
           }
           paramNameSet.add(name);
         }
         if (param instanceof Parameter.StarStar) {
           hasStarStar = true;
           starStar = name;
         } else if (param instanceof Parameter.Star) {
           if (hasStar) {
             throw new SignatureException(
                 "duplicate star parameter in function definition", param);
           }
           hasStar = true;
           defaultRequired = false;
           if (param.getName() != null) {
             star = name;
           }
         } else if (hasStar && param instanceof Parameter.Optional) {
           optionalNamedOnly++;
           optionalNamedOnlyParams.add(name);
           optionalNamedOnlyDefaultValues.add(param.getDefaultValue());
         } else {
           params.add(name);
           if (param instanceof Parameter.Optional) {
             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);
       defaults.addAll(optionalNamedOnlyDefaultValues);

       if (star != null) {
         params.add(star);
       }
       if (starStar != null) {
         params.add(starStar);
       }
       return WithValues.create(
           FunctionSignature.create(
               mandatoryPositionals,
               optionalPositionals,
               mandatoryNamedOnly,
               optionalNamedOnly,
               star != null,
               starStar != null,
               ImmutableList.copyOf(params)),
           FunctionSignature.valueListOrNull(defaults),
           null);
     }

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

     /**
      * Appends a representation of this signature to a string buffer.
      *
      * @param sb Output StringBuffer
      * @param showDefaults Determines whether the default values of parameters should be printed (if
      *     present)
      * @param showTypes Determines whether parameter type information should be shown
      * @param skipFirstMandatory Determines whether the first mandatory parameter should be omitted.
      */
     public StringBuilder toStringBuilder(
         final StringBuilder sb,
         final boolean showDefaults,
         final boolean showTypes,
         final boolean skipFirstMandatory) {
       FunctionSignature sig = getSignature();
       final BasePrinter printer = Printer.getPrinter(sb);
       final ImmutableList<String> names = sig.getParameterNames();
       @Nullable final List<V> defaultValues = getDefaultValues();
       @Nullable final List<T> types = getTypes();

       int mandatoryPositionals = sig.numMandatoryPositionals();
       int optionalPositionals = sig.numOptionalPositionals();
       int mandatoryNamedOnly = sig.numMandatoryNamedOnly();
       int optionalNamedOnly = sig.numOptionalNamedOnly();
       boolean hasVarargs = sig.hasVarargs();
       boolean hasKwargs = sig.hasKwargs();
       int positionals = mandatoryPositionals + optionalPositionals;
       int namedOnly = mandatoryNamedOnly + optionalNamedOnly;
       int named = positionals + namedOnly;
       int args = named + (hasVarargs ? 1 : 0) + (hasKwargs ? 1 : 0);
       int endMandatoryNamedOnly = positionals + mandatoryNamedOnly;
       boolean hasStar = hasVarargs || (namedOnly > 0);
       int iStarArg = named;
       int iKwArg = args - 1;

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

         public void comma() {
           if (isMore) {
             printer.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 typeDefined = types != null && types.get(i) != null;
           if (typeDefined && showTypes) {
             printer.append(": ");
             printer.append(types.get(i).toString());
           }
         }
         public void mandatory(int i) {
           comma();
           printer.append(names.get(i));
           type(i);
         }
         public void optional(int i) {
           mandatory(i);
           if (showDefaults) {
             printer.append(" = ");
             if (defaultValues == null) {
               printer.append("?");
             } else {
               printer.repr(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();
         printer.append("*");
         if (hasVarargs) {
           printer.append(names.get(iStarArg));
         }
       }
       for (; i < endMandatoryNamedOnly; i++) {
         show.mandatory(i);
       }
       for (; i < named; i++) {
         show.optional(i);
       }
       if (hasKwargs) {
         show.comma();
         printer.append("**");
         printer.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 hasVarargs whether function is variadic parameter
    * @param hasKwargs whether function accepts arbitrary named arguments
    * @param names an Array of String for the parameter names
    * @return a FunctionSignature
    */
   public static FunctionSignature of(
       int numMandatoryPositionals,
       int numOptionalPositionals,
       int numMandatoryNamedOnly,
       boolean hasVarargs,
       boolean hasKwargs,
       String... names) {
     return create(
         numMandatoryPositionals,
         numOptionalPositionals,
         numMandatoryNamedOnly,
         names.length
             - (hasKwargs ? 1 : 0)
             - (hasVarargs ? 1 : 0)
             - numMandatoryPositionals
             - numOptionalPositionals
             - numMandatoryNamedOnly,
         hasVarargs,
         hasKwargs,
         ImmutableList.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 parameter 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 parameter 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 parameters and put them in a kwarg parameter */
   public static final FunctionSignature KWARGS =
       FunctionSignature.of(0, 0, 0, false, true, "kwargs");
 }
	// Copyright 2014 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 static com.google.common.collect.ImmutableList.toImmutableList;

	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.devtools.build.lib.concurrent.BlazeInterners;
	import com.google.devtools.build.lib.skyframe.serialization.autocodec.AutoCodec;
	import com.google.devtools.build.lib.syntax.Printer.BasePrinter;
	import com.google.devtools.build.lib.util.StringCanonicalizer;
	import java.util.ArrayList;
	import java.util.Collections;
	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>Starlark's function signatures are just like Python3's. A function may have 6 kinds of
	* parameters: positional mandatory, positional optional, positional rest (aka *args or variadic
	* parameter), keyword-only mandatory, keyword-only optional, keyword rest (aka **kwargs parameter).
	* A caller may specify all arguments but the args and *kwargs arguments by name, and thus all
	* mandatory and optional parameters are named parameters.
	*
	* <p>To enable various optimizations in the argument processing routine, we sort parameters
	* 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 is no loop over a contiguous chunk of
	* them, anyway.
	* <li>The named are all grouped together, with star and star_star rest parameters coming last.
	* <li>Mandatory parameters in each category (positional and named-only) come before the optional
	* parameters, 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 order: positional mandatory parameters (if any),
	* positional optional parameters (if any), key-only mandatory parameters (if any), key-only
	* optional parameters (if any), then star parameter (if any), then star_star parameter (if any).
	*/
	@AutoCodec
	@AutoValue
	public abstract class FunctionSignature {

	// These abstract getters specify the actual parameter count fields to be defined by AutoValue.

	/** Number of mandatory positional parameters */
	public abstract int numMandatoryPositionals();

	/** Number of optional positional parameters */
	public abstract int numOptionalPositionals();

	/** Number of mandatory named-only parameters. */
	public abstract int numMandatoryNamedOnly();

	/** Number of optional named-only parameters */
	public abstract int numOptionalNamedOnly();

	/** True if function has variadic parameter, {@code def f(args)}. /
	public abstract boolean hasVarargs();

	/ True if function has residual keyword-argument parameter, {@code def f(kwargs)}. */
	public abstract boolean hasKwargs();

	/** Parameter names. */
	public abstract ImmutableList<String> getParameterNames();

	// computed parameter counts

	/** Number of optional and mandatory positional parameters. */
	public int numPositionals() {
	return numMandatoryPositionals() + numOptionalPositionals();
	}

	/** Number of optional and mandatory named-only parameters. */
	public int numNamedOnly() {
	return numMandatoryNamedOnly() + numOptionalNamedOnly();
	}

	/** number of optional parameters. */
	public int numOptionals() {
	return numOptionalPositionals() + numOptionalNamedOnly();
	}

	/** number of all named parameters: mandatory and optional of positionals and named-only */
	public int numAllNamed() {
	return numPositionals() + numNamedOnly();
	}

	/** total number of parameters */
	public int numParameters() {
	return numAllNamed() + (hasVarargs() ? 1 : 0) + (hasKwargs() ? 1 : 0);
	}

	private static final Interner<ImmutableList<String>> namesInterner =
	BlazeInterners.newWeakInterner();

	/** Intern a list of names. */
	private static ImmutableList<String> names(List<String> names) {
	return namesInterner.intern(
	names.stream().map(StringCanonicalizer::intern).collect(toImmutableList()));
	}

	// Interner.
	// Are there really a significant number of duplicates? Why??
	private static final Interner<FunctionSignature> signatureInterner =
	BlazeInterners.newWeakInterner();

	// TODO(adonovan): not a user-friendly API. Provide external callers with this function:
	// FunctionSignature.parse("a, b=1, , c, d=2, args, **kwargs")
	// implemented by invoking the Starlark parser. (Most uses are in tests.)
	@AutoCodec.Instantiator
	public static FunctionSignature create(
	int numMandatoryPositionals,
	int numOptionalPositionals,
	int numMandatoryNamedOnly,
	int numOptionalNamedOnly,
	boolean hasVarargs,
	boolean hasKwargs,
	ImmutableList<String> parameterNames) {
	Preconditions.checkArgument(
	0 <= numMandatoryPositionals
	&& 0 <= numOptionalPositionals
	&& 0 <= numMandatoryNamedOnly
	&& 0 <= numOptionalNamedOnly);

	FunctionSignature sig =
	new AutoValue_FunctionSignature(
	numMandatoryPositionals,
	numOptionalPositionals,
	numMandatoryNamedOnly,
	numOptionalNamedOnly,
	hasVarargs,
	hasKwargs,
	names(parameterNames));

	Preconditions.checkArgument(parameterNames.size() == sig.numParameters());
	return signatureInterner.intern(sig);
	}

	/** 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 StarlarkFunction), 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>.
	*/
	@AutoCodec
	@AutoValue
	public abstract static class WithValues<V, T> {

	/** the underlying parameter signature */
	public abstract FunctionSignature getSignature();

	/**
	* The default values (if any) as an unmodifiable List of one per optional parameter. May
	* contain nulls.
	*/
	@Nullable public abstract List<V> getDefaultValues();

	/**
	* The parameter types (if specified) as an unmodifiable List of one per parameter, including *
	* and **. May contain nulls.
	*/
	@Nullable public abstract List<T> getTypes();

	/** Create a signature with (default and type) values. */
	public static <V, T> WithValues<V, T> create(FunctionSignature signature,
	@Nullable List<V> defaultValues, @Nullable List<T> types) {
	List<V> convertedDefaultValues = null;
	if (defaultValues != null) {
	Preconditions.checkArgument(defaultValues.size() == signature.numOptionals());
	List<V> copiedDefaultValues = new ArrayList<>();
	copiedDefaultValues.addAll(defaultValues);
	convertedDefaultValues = Collections.unmodifiableList(copiedDefaultValues);
	}
	List<T> convertedTypes = null;
	if (types != null) {
	Preconditions.checkArgument(types.size() == signature.numParameters());
	List<T> copiedTypes = new ArrayList<>();
	copiedTypes.addAll(types);
	convertedTypes = Collections.unmodifiableList(copiedTypes);
	}
	return createInternal(signature, convertedDefaultValues, convertedTypes);
	}

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

	@AutoCodec.VisibleForSerialization
	@AutoCodec.Instantiator
	static <V, T> WithValues<V, T> createInternal(
	FunctionSignature signature, @Nullable List<V> defaultValues, @Nullable List<T> types) {
	return new AutoValue_FunctionSignature_WithValues<>(signature, defaultValues, types);
	}

	/** Convert a list of Parameter into a FunctionSignature. */
	// TODO(adonovan): inline into parser (or validator) and simplify.
	static WithValues<Expression, Expression> fromParameters(Iterable<Parameter> 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;
	ArrayList<String> params = new ArrayList<>();
	ArrayList<Expression> defaults = new ArrayList<>();
	// optional named-only parameters are kept aside to be spliced after the mandatory ones.
	ArrayList<String> optionalNamedOnlyParams = new ArrayList<>();
	ArrayList<Expression> 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 param : parameters) {
	if (hasStarStar) {
	throw new SignatureException("illegal parameter after star-star parameter", param);
	}
	@Nullable String name = param.getName();
	if (param.getName() != null) {
	if (paramNameSet.contains(name)) {
	throw new SignatureException("duplicate parameter name in function definition", param);
	}
	paramNameSet.add(name);
	}
	if (param instanceof Parameter.StarStar) {
	hasStarStar = true;
	starStar = name;
	} else if (param instanceof Parameter.Star) {
	if (hasStar) {
	throw new SignatureException(
	"duplicate star parameter in function definition", param);
	}
	hasStar = true;
	defaultRequired = false;
	if (param.getName() != null) {
	star = name;
	}
	} else if (hasStar && param instanceof Parameter.Optional) {
	optionalNamedOnly++;
	optionalNamedOnlyParams.add(name);
	optionalNamedOnlyDefaultValues.add(param.getDefaultValue());
	} else {
	params.add(name);
	if (param instanceof Parameter.Optional) {
	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);
	defaults.addAll(optionalNamedOnlyDefaultValues);

	if (star != null) {
	params.add(star);
	}
	if (starStar != null) {
	params.add(starStar);
	}
	return WithValues.create(
	FunctionSignature.create(
	mandatoryPositionals,
	optionalPositionals,
	mandatoryNamedOnly,
	optionalNamedOnly,
	star != null,
	starStar != null,
	ImmutableList.copyOf(params)),
	FunctionSignature.valueListOrNull(defaults),
	null);
	}

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

	/**
	* Appends a representation of this signature to a string buffer.
	*
	* @param sb Output StringBuffer
	* @param showDefaults Determines whether the default values of parameters should be printed (if
	* present)
	* @param showTypes Determines whether parameter type information should be shown
	* @param skipFirstMandatory Determines whether the first mandatory parameter should be omitted.
	*/
	public StringBuilder toStringBuilder(
	final StringBuilder sb,
	final boolean showDefaults,
	final boolean showTypes,
	final boolean skipFirstMandatory) {
	FunctionSignature sig = getSignature();
	final BasePrinter printer = Printer.getPrinter(sb);
	final ImmutableList<String> names = sig.getParameterNames();
	@Nullable final List<V> defaultValues = getDefaultValues();
	@Nullable final List<T> types = getTypes();

	int mandatoryPositionals = sig.numMandatoryPositionals();
	int optionalPositionals = sig.numOptionalPositionals();
	int mandatoryNamedOnly = sig.numMandatoryNamedOnly();
	int optionalNamedOnly = sig.numOptionalNamedOnly();
	boolean hasVarargs = sig.hasVarargs();
	boolean hasKwargs = sig.hasKwargs();
	int positionals = mandatoryPositionals + optionalPositionals;
	int namedOnly = mandatoryNamedOnly + optionalNamedOnly;
	int named = positionals + namedOnly;
	int args = named + (hasVarargs ? 1 : 0) + (hasKwargs ? 1 : 0);
	int endMandatoryNamedOnly = positionals + mandatoryNamedOnly;
	boolean hasStar = hasVarargs \|\| (namedOnly > 0);
	int iStarArg = named;
	int iKwArg = args - 1;

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

	public void comma() {
	if (isMore) {
	printer.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 typeDefined = types != null && types.get(i) != null;
	if (typeDefined && showTypes) {
	printer.append(": ");
	printer.append(types.get(i).toString());
	}
	}
	public void mandatory(int i) {
	comma();
	printer.append(names.get(i));
	type(i);
	}
	public void optional(int i) {
	mandatory(i);
	if (showDefaults) {
	printer.append(" = ");
	if (defaultValues == null) {
	printer.append("?");
	} else {
	printer.repr(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();
	printer.append("*");
	if (hasVarargs) {
	printer.append(names.get(iStarArg));
	}
	}
	for (; i < endMandatoryNamedOnly; i++) {
	show.mandatory(i);
	}
	for (; i < named; i++) {
	show.optional(i);
	}
	if (hasKwargs) {
	show.comma();
	printer.append("**");
	printer.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 hasVarargs whether function is variadic parameter
	* @param hasKwargs whether function accepts arbitrary named arguments
	* @param names an Array of String for the parameter names
	* @return a FunctionSignature
	*/
	public static FunctionSignature of(
	int numMandatoryPositionals,
	int numOptionalPositionals,
	int numMandatoryNamedOnly,
	boolean hasVarargs,
	boolean hasKwargs,
	String... names) {
	return create(
	numMandatoryPositionals,
	numOptionalPositionals,
	numMandatoryNamedOnly,
	names.length
	- (hasKwargs ? 1 : 0)
	- (hasVarargs ? 1 : 0)
	- numMandatoryPositionals
	- numOptionalPositionals
	- numMandatoryNamedOnly,
	hasVarargs,
	hasKwargs,
	ImmutableList.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 parameter 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 parameter 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 parameters and put them in a kwarg parameter */
	public static final FunctionSignature KWARGS =
	FunctionSignature.of(0, 0, 0, false, true, "kwargs");
	}