Add warning message empty THEN clause

Author: MartyIX

src/compiler/checker.ts

@@ -12227,6 +12227,11 @@ namespace ts {
 
             checkExpression(node.expression);
             checkSourceElement(node.thenStatement);
+
+            if (node.thenStatement.kind === SyntaxKind.EmptyStatement) {
+                error(node.thenStatement, Diagnostics.The_body_of_an_if_statement_cannot_be_the_empty_statement);
+            }
+
             checkSourceElement(node.elseStatement);
         }
 

src/compiler/diagnosticMessages.json

@@ -2469,5 +2469,9 @@
     "A type assertion expression is not allowed in the left-hand side of an exponentiation expression. Consider enclosing the expression in parentheses.": {
       "category": "Error",
       "code": 17007
+    },
+    "The body of an 'if' statement cannot be the empty statement.": {
+      "category": "Warning",
+      "code": 20000
     }
 }

tests/baselines/reference/emptyThenWarning.errors.txt

@@ -0,0 +1,15 @@
+tests/cases/compiler/emptyThenWarning.ts(1,6): warning TS20000: The body of an 'if' statement cannot be the empty statement.
+tests/cases/compiler/emptyThenWarning.ts(4,19): warning TS20000: The body of an 'if' statement cannot be the empty statement.
+
+
+==== tests/cases/compiler/emptyThenWarning.ts (2 errors) ====
+    if(1);
+         ~
+!!! warning TS20000: The body of an 'if' statement cannot be the empty statement.
+    
+    let x = 0;
+    if (true === true); {  
+                      ~
+!!! warning TS20000: The body of an 'if' statement cannot be the empty statement.
+        x = 1;
+    }

tests/baselines/reference/emptyThenWarning.js

@@ -0,0 +1,17 @@
+//// [emptyThenWarning.ts]
+if(1);
+
+let x = 0;
+if (true === true); {  
+    x = 1;
+}
+
+//// [emptyThenWarning.js]
+if (1)
+    ;
+var x = 0;
+if (true === true)
+    ;
+{
+    x = 1;
+}

tests/baselines/reference/emptyThenWithoutWarning.js

@@ -0,0 +1,16 @@
+//// [emptyThenWithoutWarning.ts]
+let a = 4;
+
+if(a === 1 || a === 2 || a === 3) {
+}
+else {
+    let message = "Ooops";
+}
+
+//// [emptyThenWithoutWarning.js]
+var a = 4;
+if (a === 1 || a === 2 || a === 3) {
+}
+else {
+    var message = "Ooops";
+}

tests/baselines/reference/emptyThenWithoutWarning.symbols

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/emptyThenWithoutWarning.ts ===
+let a = 4;
+>a : Symbol(a, Decl(emptyThenWithoutWarning.ts, 0, 3))
+
+if(a === 1 || a === 2 || a === 3) {
+>a : Symbol(a, Decl(emptyThenWithoutWarning.ts, 0, 3))
+>a : Symbol(a, Decl(emptyThenWithoutWarning.ts, 0, 3))
+>a : Symbol(a, Decl(emptyThenWithoutWarning.ts, 0, 3))
+}
+else {
+    let message = "Ooops";
+>message : Symbol(message, Decl(emptyThenWithoutWarning.ts, 5, 7))
+}

tests/baselines/reference/emptyThenWithoutWarning.types

@@ -0,0 +1,23 @@
+=== tests/cases/compiler/emptyThenWithoutWarning.ts ===
+let a = 4;
+>a : number
+>4 : number
+
+if(a === 1 || a === 2 || a === 3) {
+>a === 1 || a === 2 || a === 3 : boolean
+>a === 1 || a === 2 : boolean
+>a === 1 : boolean
+>a : number
+>1 : number
+>a === 2 : boolean
+>a : number
+>2 : number
+>a === 3 : boolean
+>a : number
+>3 : number
+}
+else {
+    let message = "Ooops";
+>message : string
+>"Ooops" : string
+}

tests/cases/compiler/emptyThenWarning.ts

@@ -0,0 +1,6 @@
+if(1);
+
+let x = 0;
+if (true === true); {  
+    x = 1;
+}

tests/cases/compiler/emptyThenWithoutWarning.ts

@@ -0,0 +1,7 @@
+let a = 4;
+
+if(a === 1 || a === 2 || a === 3) {
+}
+else {
+    let message = "Ooops";
+}