Implement if(let ...) syntax (#3673) (#3958)

6 files changed, 388 insertions, 1 deletions

diff --git a/docs/user-guide/06-interfaces-generics.md b/docs/user-guide/06-interfaces-generics.md
index ba543df56..cb6a5070e 100644
--- a/docs/user-guide/06-interfaces-generics.md
+++ b/docs/user-guide/06-interfaces-generics.md
@@ -677,6 +677,64 @@ T compute<T>(T a1, T a2)
 // compute(3, 1) == 2
 ```
 
+`as` operator can also be used in the `if` predicate to test if an object can be casted to a specific type, once the cast test is successful,
+the object can be used in the `if` block as the casted type without the need to retrieve the `Optional<T>::value` property:
+```csharp
+interface IFoo
+{
+    void foo();
+}
+
+struct MyImpl1 : IFoo
+{
+    void foo() { printf("MyImpl1");}
+}
+
+struct MyImpl2 : IFoo
+{
+    void foo() { printf("MyImpl2");}
+}
+
+struct MyImpl3 : IFoo
+{
+    void foo() { printf("MyImpl3");}
+}
+
+void test(IFoo foo)
+{
+    // This syntax will be desugared to the following:
+    // {
+    //      Optional<MyImpl1> $OptVar = foo as MyImpl1;
+    //      if ($OptVar.hasValue)
+    //      {
+    //          MyImpl1 t = $OptVar.value;
+    //          t.foo();
+    //      }
+    //      else if ...
+    // }
+    if (let t = foo as MyImpl1) // t is of type MyImpl1
+    {
+        t.foo();
+    }
+    else if (let t = foo as MyImpl2) // t is of type MyImpl2
+    {
+        t.foo();
+    }
+    else
+        printf("fail");
+}
+
+void main()
+{
+    MyImpl1 v1;
+    test(v1);
+
+    MyImpl2 v2;
+    test(v2);
+}
+
+```
+
 Extensions to Interfaces
 -----------------------------
 
diff --git a/source/slang/slang-parser.cpp b/source/slang/slang-parser.cpp
index e564b4956..2c304a663 100644
--- a/source/slang/slang-parser.cpp
+++ b/source/slang/slang-parser.cpp
@@ -199,6 +199,7 @@ namespace Slang
         Stmt* parseLabelStatement();
         DeclStmt* parseVarDeclrStatement(Modifiers modifiers);
         IfStmt* parseIfStatement();
+        Stmt* parseIfLetStatement();
         ForStmt* ParseForStatement();
         WhileStmt* ParseWhileStatement();
         DoWhileStmt* ParseDoWhileStatement();
@@ -5276,7 +5277,16 @@ namespace Slang
         if (LookAheadToken(TokenType::LBrace))
             statement = parseBlockStatement();
         else if (LookAheadToken("if"))
-            statement = parseIfStatement();
+        {
+            if(LookAheadToken("let", 2))
+            {
+                statement = parseIfLetStatement();
+            }
+            else
+            {
+                statement = parseIfStatement();
+            }
+        }
         else if (LookAheadToken("for"))
             statement = ParseForStatement();
         else if (LookAheadToken("while"))
@@ -5579,6 +5589,103 @@ namespace Slang
         return varDeclrStatement;
     }
 
+    static Expr* constructIfLetPredicate(Parser* parser, VarExpr* varExpr)
+    {
+        // create a "var.hasValue" expression
+        MemberExpr* memberExpr = parser->astBuilder->create<MemberExpr>();
+        memberExpr->baseExpression = varExpr;
+        parser->FillPosition(memberExpr);
+        memberExpr->name = getName(parser, "hasValue");
+
+        return memberExpr;
+    }
+
+    // Parse the syntax 'if (let var = X as Y)'
+    Stmt* Parser::parseIfLetStatement()
+    {
+        ScopeDecl* scopeDecl = astBuilder->create<ScopeDecl>();
+        pushScopeAndSetParent(scopeDecl);
+
+        SeqStmt* newBody = astBuilder->create<SeqStmt>();
+
+        IfStmt* ifStatement = astBuilder->create<IfStmt>();
+        FillPosition(ifStatement);
+        ReadToken("if");
+        ReadToken(TokenType::LParent);
+
+        // parse 'let var = X as Y'
+        ReadToken("let");
+        auto identifierToken = ReadToken(TokenType::Identifier);
+        ReadToken(TokenType::OpAssign);
+        auto initExpr = ParseInitExpr();
+
+        // insert 'let tempVarDecl = X as Y;'
+        auto tempVarDecl = astBuilder->create<LetDecl>();
+        tempVarDecl->nameAndLoc = NameLoc(getName(this, "$OptVar"), identifierToken.loc);
+        tempVarDecl->initExpr = initExpr;
+        AddMember(currentScope->containerDecl, tempVarDecl);
+
+        DeclStmt* tmpVarDeclStmt = astBuilder->create<DeclStmt>();
+        FillPosition(tmpVarDeclStmt);
+        tmpVarDeclStmt->decl = tempVarDecl;
+        newBody->stmts.add(tmpVarDeclStmt);
+
+        // construct 'if (tempVarDecl.hasValue == true)'
+        VarExpr* tempVarExpr = astBuilder->create<VarExpr>();
+        tempVarExpr->scope = currentScope;
+        FillPosition(tempVarExpr);
+        tempVarExpr->name = tempVarDecl->getName();
+        ifStatement->predicate = constructIfLetPredicate(this, tempVarExpr);
+
+        ReadToken(TokenType::RParent);
+
+        // Create a new scope surrounding the positive statement, will be used for
+        // the variable declared in the if_let syntax
+        ScopeDecl* positiveScopeDecl = astBuilder->create<ScopeDecl>();
+        pushScopeAndSetParent(positiveScopeDecl);
+        ifStatement->positiveStatement = ParseStatement(ifStatement);
+        PopScope();
+
+        if (LookAheadToken("else"))
+        {
+            ReadToken("else");
+            ifStatement->negativeStatement = ParseStatement(ifStatement);
+        }
+
+        if (ifStatement->positiveStatement)
+        {
+            auto seqPositiveStmt = as<SeqStmt>(ifStatement->positiveStatement);
+            if (!seqPositiveStmt)
+            {
+                seqPositiveStmt = astBuilder->create<SeqStmt>();
+            }
+
+            MemberExpr* memberExpr = astBuilder->create<MemberExpr>();
+            memberExpr->baseExpression = tempVarExpr;
+            memberExpr->name = getName(this, "value");
+
+            auto varDecl = astBuilder->create<LetDecl>();
+            varDecl->nameAndLoc = NameLoc(identifierToken.getName(), identifierToken.loc);
+            varDecl->initExpr = memberExpr;
+
+            DeclStmt* varDeclrStatement = astBuilder->create<DeclStmt>();
+            varDeclrStatement->decl = varDecl;
+
+            // Add scope to the variable declared in the if_let syntax such
+            // that this variable cannot be used outside the positive statement
+            AddMember(positiveScopeDecl, varDecl);
+
+            seqPositiveStmt->stmts.add(varDeclrStatement);
+            seqPositiveStmt->stmts.add(ifStatement->positiveStatement);
+            ifStatement->positiveStatement = seqPositiveStmt;
+        }
+
+        newBody->stmts.add(ifStatement);
+        PopScope();
+
+        return newBody;
+    }
+
     IfStmt* Parser::parseIfStatement()
     {
         IfStmt* ifStatement = astBuilder->create<IfStmt>();
diff --git a/tests/language-feature/if-let/if-let-1.slang b/tests/language-feature/if-let/if-let-1.slang
new file mode 100644
index 000000000..c197f26ea
--- /dev/null
+++ b/tests/language-feature/if-let/if-let-1.slang
@@ -0,0 +1,89 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -cpu -compute -shaderobj
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -cuda -compute -shaderobj
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-vk -compute -shaderobj
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0 0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+
+interface IFoo
+{
+    int foo(int a);
+}
+
+struct MyImpl1 : IFoo
+{
+    int foo(int a) { return a; }
+}
+
+struct MyImpl2 : IFoo
+{
+    int foo(int a) { return a + 5; }
+}
+
+int test(IFoo foo, int idx)
+{
+    int val = 0;
+    if (let a = foo as MyImpl1)
+    {
+        val = a.foo(idx);
+    }
+    else if (let a = foo as MyImpl2)
+    {
+        val = a.foo(idx);
+    }
+    return (val);
+}
+
+int test1<T>(T t)
+{
+    if (let a = t as uint)
+    {
+        return 1;
+    }
+    else if(let a = t as float)
+    {
+        return 2;
+    }
+    else if (let a = t as double)
+    {
+        return 3;
+    }
+    else if (let a = t as int)
+    {
+        return 4;
+    }
+    else if (let a = t as uint64_t)
+    {
+        return 5;
+    }
+    else
+    {
+        return 6;
+    }
+}
+
+
+[numthreads(1, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    MyImpl1 impl1;
+    MyImpl2 impl2;
+    // CHECK: 1
+    // CHECK: 7
+    outputBuffer[0] = test(impl1, 1);
+    outputBuffer[1] = test(impl2, 2);
+
+    // CHECK: 1
+    outputBuffer[2] = test1(2U);
+    // CHECK: 2
+    outputBuffer[3] = test1(2.0f);
+    // CHECK: 3
+    outputBuffer[4] = test1(2.0lf);
+    // CHECK: 4
+    outputBuffer[5] = test1(2);
+    // CHECK: 5
+    outputBuffer[6] = test1(2LLU);
+    // CHECK: 6
+    outputBuffer[7] = test1(impl1);
+}
diff --git a/tests/language-feature/if-let/if-let-diagnose-1.slang b/tests/language-feature/if-let/if-let-diagnose-1.slang
new file mode 100644
index 000000000..2322abb1a
--- /dev/null
+++ b/tests/language-feature/if-let/if-let-diagnose-1.slang
@@ -0,0 +1,53 @@
+//TEST:SIMPLE(filecheck=CHECK): -target glsl -stage compute -entry computeMain
+//TEST:SIMPLE(filecheck=CHECK): -target hlsl -stage compute -entry computeMain
+//TEST:SIMPLE(filecheck=CHECK): -target cuda -stage compute -entry computeMain
+//TEST:SIMPLE(filecheck=CHECK): -target cpp -stage compute -entry computeMain
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+
+interface IFoo
+{
+    int foo(int a);
+}
+
+struct MyImpl : IFoo
+{
+    int foo(int a) { return a; }
+}
+
+struct MyImpl1 : IFoo
+{
+    int foo(int a) { return a; }
+}
+
+int test(IFoo foo, int idx)
+{
+    int val = 0;
+    if (let a = foo as MyImpl)
+    {
+        val = a.foo(idx);
+    }
+    // CHECK: error 30015: undefined identifier 'a'.
+    else if(a == none)
+    {
+        val = -1;
+    }
+    else
+    {
+        // CHECK: error 30015: undefined identifier 'a'.
+        if (a == none)
+        {
+            val = -1;
+        }
+    }
+    return (val);
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    MyImpl1 impl;
+    outputBuffer[dispatchThreadID.x] = test(impl, dispatchThreadID.x);
+}
diff --git a/tests/language-feature/if-let/if-let-diagnose.slang b/tests/language-feature/if-let/if-let-diagnose.slang
new file mode 100644
index 000000000..4e9aa69c7
--- /dev/null
+++ b/tests/language-feature/if-let/if-let-diagnose.slang
@@ -0,0 +1,42 @@
+//TEST:SIMPLE(filecheck=CHECK): -target glsl -stage compute -entry computeMain
+//TEST:SIMPLE(filecheck=CHECK): -target hlsl -stage compute -entry computeMain
+//TEST:SIMPLE(filecheck=CHECK): -target cuda -stage compute -entry computeMain
+//TEST:SIMPLE(filecheck=CHECK): -target cpp -stage compute -entry computeMain
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+
+interface IFoo
+{
+    int foo(int a);
+}
+
+struct MyImpl : IFoo
+{
+    int foo(int a) { return a; }
+}
+
+struct MyImpl1 : IFoo
+{
+    int foo(int a) { return a; }
+}
+
+int test(IFoo foo, int idx)
+{
+    int val = 0;
+    // CHECK: error 20002: syntax error.
+    if ((let a = foo as MyImpl))
+    {
+        val = a.foo(idx);
+    }
+    return (val);
+}
+
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    MyImpl impl;
+    outputBuffer[dispatchThreadID.x] = test(impl, dispatchThreadID.x);
+}
diff --git a/tests/language-feature/if-let/if-let.slang b/tests/language-feature/if-let/if-let.slang
new file mode 100644
index 000000000..5bb31030f
--- /dev/null
+++ b/tests/language-feature/if-let/if-let.slang
@@ -0,0 +1,38 @@
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -cpu -compute -shaderobj
+//TEST(compute):COMPARE_COMPUTE(filecheck-buffer=CHECK): -cuda -compute -shaderobj
+//TEST(compute, vulkan):COMPARE_COMPUTE_EX(filecheck-buffer=CHECK):-vk -compute -shaderobj
+
+//TEST_INPUT:ubuffer(data=[0 0 0 0], stride=4):out,name=outputBuffer
+RWStructuredBuffer<int> outputBuffer;
+
+
+interface IFoo
+{
+    int foo(int a);
+}
+
+struct MyImpl : IFoo
+{
+    int foo(int a) { return a; }
+}
+
+int test(IFoo foo, int idx)
+{
+    int val = 0;
+    if (let a = foo as MyImpl)
+    {
+        val = a.foo(idx);
+    }
+    return (val);
+}
+
+[numthreads(4, 1, 1)]
+void computeMain(uint3 dispatchThreadID: SV_DispatchThreadID)
+{
+    MyImpl impl;
+    // CHECK: 0
+    // CHECK: 1
+    // CHECK: 2
+    // CHECK: 3
+    outputBuffer[dispatchThreadID.x] = test(impl, dispatchThreadID.x);
+}