Support ternary operator in PowerShell language (PowerShell#10367)

Author: daxian-dbw

src/System.Management.Automation/engine/CommandCompletion/CompletionCompleters.cs

@@ -6991,6 +6991,13 @@ public object VisitPipeline(PipelineAst pipelineAst)
             return expr != null && (bool)expr.Accept(this);
         }
 
+        public object VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst)
+        {
+            return (bool)ternaryExpressionAst.Condition.Accept(this) &&
+                   (bool)ternaryExpressionAst.IfTrue.Accept(this) &&
+                   (bool)ternaryExpressionAst.IfFalse.Accept(this);
+        }
+
         public object VisitBinaryExpression(BinaryExpressionAst binaryExpressionAst)
         {
             return (bool)binaryExpressionAst.Left.Accept(this) && (bool)binaryExpressionAst.Right.Accept(this);

src/System.Management.Automation/engine/ExperimentalFeature/ExperimentalFeature.cs

@@ -111,7 +111,10 @@ static ExperimentalFeature()
                     description: "Recommend potential commands based on fuzzy search on a CommandNotFoundException"),
                 new ExperimentalFeature(
                     name: "PSForEachObjectParallel",
-                    description: "New parameter set for ForEach-Object to run script blocks in parallel")
+                    description: "New parameter set for ForEach-Object to run script blocks in parallel"),
+                new ExperimentalFeature(
+                    name: "PSTernaryOperator",
+                    description: "Support the ternary operator in PowerShell langauge.")
             };
             EngineExperimentalFeatures = new ReadOnlyCollection<ExperimentalFeature>(engineFeatures);
 

src/System.Management.Automation/engine/Modules/ScriptAnalysis.cs

@@ -258,6 +258,8 @@ public override AstVisitAction VisitAssignmentStatement(AssignmentStatementAst a
 
         public override AstVisitAction VisitSwitchStatement(SwitchStatementAst switchStatementAst) { return AstVisitAction.SkipChildren; }
 
+        public override AstVisitAction VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst) { return AstVisitAction.SkipChildren; }
+
         // Visit one the other variations:
         //  - Dotting scripts
         //  - Setting aliases

src/System.Management.Automation/engine/parser/AstVisitor.cs

@@ -4,7 +4,6 @@
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
 using System.Linq;
-using System.Reflection;
 using System.Reflection.Emit;
 
 namespace System.Management.Automation.Language
@@ -151,6 +150,8 @@ public interface ICustomAstVisitor
     /// <summary/>
     public interface ICustomAstVisitor2 : ICustomAstVisitor
     {
+        private object DefaultVisit(Ast ast) => null;
+
         /// <summary/>
         object VisitTypeDefinition(TypeDefinitionAst typeDefinitionAst);
 
@@ -171,6 +172,9 @@ public interface ICustomAstVisitor2 : ICustomAstVisitor
 
         /// <summary/>
         object VisitDynamicKeywordStatement(DynamicKeywordStatementAst dynamicKeywordAst);
+
+        /// <summary/>
+        object VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst) => DefaultVisit(ternaryExpressionAst);
     }
 
 #if DEBUG
@@ -312,6 +316,8 @@ internal AstVisitAction CheckParent(Ast ast)
         public override AstVisitAction VisitConfigurationDefinition(ConfigurationDefinitionAst ast) { return CheckParent(ast); }
 
         public override AstVisitAction VisitDynamicKeywordStatement(DynamicKeywordStatementAst ast) { return CheckParent(ast); }
+
+        public override AstVisitAction VisitTernaryExpression(TernaryExpressionAst ast) => CheckParent(ast);
     }
 
     /// <summary>
@@ -544,6 +550,8 @@ protected AstVisitAction CheckScriptBlock(Ast ast)
         public override AstVisitAction VisitConfigurationDefinition(ConfigurationDefinitionAst ast) { return Check(ast); }
 
         public override AstVisitAction VisitDynamicKeywordStatement(DynamicKeywordStatementAst ast) { return Check(ast); }
+
+        public override AstVisitAction VisitTernaryExpression(TernaryExpressionAst ast) { return Check(ast); }
     }
 
     /// <summary>
@@ -680,5 +688,7 @@ public abstract class DefaultCustomAstVisitor2 : DefaultCustomAstVisitor, ICusto
         public virtual object VisitTypeDefinition(TypeDefinitionAst typeDefinitionAst) { return null; }
         /// <summary/>
         public virtual object VisitFunctionMember(FunctionMemberAst functionMemberAst) { return null; }
+        /// <summary/>
+        public virtual object VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst) { return null; }
     }
 }

src/System.Management.Automation/engine/parser/CharTraits.cs

@@ -374,13 +374,26 @@ internal static bool ForceStartNewToken(this char c)
             return c.IsWhitespace();
         }
 
-        // Return true if the character ends the current number token.  This allows the tokenizer
-        // to scan '7z' as a single token, but '7+' as 2 tokens.
-        internal static bool ForceStartNewTokenAfterNumber(this char c)
+        /// <summary>
+        /// Check if the current character forces to end scanning a number token.
+        /// This allows the tokenizer to scan '7z' as a single token, but '7+' as 2 tokens.
+        /// </summary>
+        /// <param name="c">The character to check.</param>
+        /// <param name="forceEndNumberOnTernaryOperatorChars">
+        /// In some cases, we want '?' and ':' to end a number token too, so they can be
+        /// treated as the ternary operator tokens.
+        /// </param>
+        /// <returns>Return true if the character ends the current number token.</returns>
+        internal static bool ForceStartNewTokenAfterNumber(this char c, bool forceEndNumberOnTernaryOperatorChars)
         {
             if (c < 128)
             {
-                return (s_traits[c] & CharTraits.ForceStartNewTokenAfterNumber) != 0;
+                if ((s_traits[c] & CharTraits.ForceStartNewTokenAfterNumber) != 0)
+                {
+                    return true;
+                }
+
+                return forceEndNumberOnTernaryOperatorChars && (c == '?' || c == ':');
             }
 
             return c.IsDash();

src/System.Management.Automation/engine/parser/Compiler.cs

@@ -4974,6 +4974,16 @@ public Expression GenerateCallContains(Expression lhs, Expression rhs, bool igno
                 rhs.Cast(typeof(object)));
         }
 
+        public object VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst)
+        {
+            var expr = Expression.Condition(
+                Compile(ternaryExpressionAst.Condition).Convert(typeof(bool)),
+                Compile(ternaryExpressionAst.IfTrue).Convert(typeof(object)),
+                Compile(ternaryExpressionAst.IfFalse).Convert(typeof(object)));
+
+            return expr;
+        }
+
         public object VisitBinaryExpression(BinaryExpressionAst binaryExpressionAst)
         {
             object constantValue;

src/System.Management.Automation/engine/parser/ConstantValues.cs

@@ -15,7 +15,7 @@ namespace System.Management.Automation.Language
      * There is a number of similarities between these two classes, and changes (fixes) in this code
      * may need to be reflected in that class and vice versa
      */
-    internal class IsConstantValueVisitor : ICustomAstVisitor
+    internal class IsConstantValueVisitor : ICustomAstVisitor2
     {
         public static bool IsConstant(Ast ast, out object constantValue, bool forAttribute = false, bool forRequires = false)
         {
@@ -130,6 +130,20 @@ public static bool IsConstant(Ast ast, out object constantValue, bool forAttribu
 
         public object VisitInvokeMemberExpression(InvokeMemberExpressionAst invokeMemberExpressionAst) { return false; }
 
+        public object VisitTypeDefinition(TypeDefinitionAst typeDefinitionAst) { return false; }
+
+        public object VisitPropertyMember(PropertyMemberAst propertyMemberAst) { return false; }
+
+        public object VisitFunctionMember(FunctionMemberAst functionMemberAst) { return false; }
+
+        public object VisitBaseCtorInvokeMemberExpression(BaseCtorInvokeMemberExpressionAst baseCtorInvokeMemberExpressionAst) { return false; }
+
+        public object VisitUsingStatement(UsingStatementAst usingStatement) { return false; }
+
+        public object VisitConfigurationDefinition(ConfigurationDefinitionAst configurationDefinitionAst) { return false; }
+
+        public object VisitDynamicKeywordStatement(DynamicKeywordStatementAst dynamicKeywordAst) { return false; }
+
         public object VisitStatementBlock(StatementBlockAst statementBlockAst)
         {
             if (statementBlockAst.Traps != null) return false;
@@ -172,6 +186,13 @@ private static bool IsNullDivisor(ExpressionAst operand)
             return false;
         }
 
+        public object VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst)
+        {
+            return (bool)ternaryExpressionAst.Condition.Accept(this) &&
+                   (bool)ternaryExpressionAst.IfTrue.Accept(this) &&
+                   (bool)ternaryExpressionAst.IfFalse.Accept(this);
+        }
+
         public object VisitBinaryExpression(BinaryExpressionAst binaryExpressionAst)
         {
             return binaryExpressionAst.Operator.HasTrait(TokenFlags.CanConstantFold) &&
@@ -300,7 +321,7 @@ public object VisitParenExpression(ParenExpressionAst parenExpressionAst)
         }
     }
 
-    internal class ConstantValueVisitor : ICustomAstVisitor
+    internal class ConstantValueVisitor : ICustomAstVisitor2
     {
         internal bool AttributeArgument { get; set; }
         internal bool RequiresArgument { get; set; }
@@ -400,6 +421,21 @@ private static object CompileAndInvoke(Ast ast)
 
         public object VisitInvokeMemberExpression(InvokeMemberExpressionAst invokeMemberExpressionAst) { return AutomationNull.Value; }
 
+        public object VisitTypeDefinition(TypeDefinitionAst typeDefinitionAst) { return AutomationNull.Value; }
+
+        public object VisitPropertyMember(PropertyMemberAst propertyMemberAst) { return AutomationNull.Value; }
+
+        public object VisitFunctionMember(FunctionMemberAst functionMemberAst) { return AutomationNull.Value; }
+
+        public object VisitBaseCtorInvokeMemberExpression(BaseCtorInvokeMemberExpressionAst baseCtorInvokeMemberExpressionAst) { return AutomationNull.Value; }
+
+        public object VisitUsingStatement(UsingStatementAst usingStatement) { return AutomationNull.Value; }
+
+        public object VisitConfigurationDefinition(ConfigurationDefinitionAst configurationDefinitionAst) { return AutomationNull.Value; }
+
+        public object VisitDynamicKeywordStatement(DynamicKeywordStatementAst dynamicKeywordAst) { return AutomationNull.Value; }
+
+
         public object VisitStatementBlock(StatementBlockAst statementBlockAst)
         {
             CheckIsConstant(statementBlockAst, "Caller to verify ast is constant");
@@ -412,6 +448,16 @@ public object VisitPipeline(PipelineAst pipelineAst)
             return pipelineAst.GetPureExpression().Accept(this);
         }
 
+        public object VisitTernaryExpression(TernaryExpressionAst ternaryExpressionAst)
+        {
+            CheckIsConstant(ternaryExpressionAst, "Caller to verify ast is constant");
+
+            object condition = ternaryExpressionAst.Condition.Accept(this);
+            return LanguagePrimitives.IsTrue(condition)
+                ? ternaryExpressionAst.IfTrue.Accept(this)
+                : ternaryExpressionAst.IfFalse.Accept(this);
+        }
+
         public object VisitBinaryExpression(BinaryExpressionAst binaryExpressionAst)
         {
             CheckIsConstant(binaryExpressionAst, "Caller to verify ast is constant");