Error on misplaced use strict directives

tsc/internal/binder/binder.go

@@ -1342,7 +1342,7 @@ func (b *Binder) getStrictModeIdentifierMessage(node *ast.Node) *diagnostics.Mes
 }
 
 // Should be called only on prologue directives (ast.IsPrologueDirective(node) should be true)
-func isUseStrictPrologueDirective(sourceFile *ast.SourceFile, node *ast.Node) bool {
+func IsUseStrictPrologueDirective(sourceFile *ast.SourceFile, node *ast.Node) bool {
 	nodeText := scanner.GetSourceTextOfNodeFromSourceFile(sourceFile, node.Expression(), false /*includeTrivia*/)
 	// Note: the node text must be exactly "use strict" or 'use strict'.  It is not ok for the
 	// string to contain unicode escapes (as per ES5).
@@ -1352,7 +1352,7 @@ func isUseStrictPrologueDirective(sourceFile *ast.SourceFile, node *ast.Node) bo
 func FindUseStrictPrologue(sourceFile *ast.SourceFile, statements []*ast.Node) *ast.Node {
 	for _, statement := range statements {
 		if ast.IsPrologueDirective(statement) {
-			if isUseStrictPrologueDirective(sourceFile, statement) {
+			if IsUseStrictPrologueDirective(sourceFile, statement) {
 				return statement
 			}
 		} else {

tsc/internal/checker/checker.go

@@ -7419,9 +7419,37 @@ func (c *Checker) checkUnusedRenamedBindingElements() {
 func (c *Checker) checkExpressionStatement(node *ast.Node) {
 	// Grammar checking
 	c.checkGrammarStatementInAmbientContext(node)
+	c.checkGrammarUseStrictDirective(node)
 	c.checkExpression(node.Expression())
 }
 
+func (c *Checker) checkGrammarUseStrictDirective(node *ast.Node) {
+	if !ast.IsPrologueDirective(node) || !binder.IsUseStrictPrologueDirective(ast.GetSourceFileOfNode(node), node) {
+		return
+	}
+
+	function := ast.GetContainingFunction(node)
+	if function == nil {
+		return
+	}
+	body := function.Body()
+	if body == nil || !ast.IsBlock(body) || node.Parent != body {
+		c.grammarErrorOnNode(node, diagnostics.A_use_strict_directive_must_be_at_the_top_of_a_function_body)
+		return
+	}
+
+	for _, statement := range body.Statements() {
+		if statement == node {
+			return
+		}
+		// Type-only declarations are absent from the emitted JavaScript and do not end its directive prologue.
+		if !ast.IsPrologueDirective(statement) && statement.Kind != ast.KindInterfaceDeclaration && statement.Kind != ast.KindTypeAliasDeclaration {
+			c.grammarErrorOnNode(node, diagnostics.A_use_strict_directive_must_be_at_the_top_of_a_function_body)
+			return
+		}
+	}
+}
+
 // Returns the type of an expression. Unlike checkExpression, this function is simply concerned
 // with computing the type and may not fully check all contained sub-expressions for errors.
 func (c *Checker) getTypeOfExpression(node *ast.Node) *Type {

tsc/internal/diagnostics/diagnosticMessages.json

@@ -8555,5 +8555,9 @@
     "'{0}' is not a valid meta-property for keyword 'import'. Did you mean 'meta' or 'defer'?": {
         "category": "Error",
         "code": 18061
+    },
+    "A 'use strict' directive must be at the top of a function body.": {
+        "category": "Error",
+        "code": 18064
     }
 }

tsc/testdata/baselines/reference/compiler/strictModeInConstructor.errors.txt

@@ -1,8 +1,12 @@
+strictModeInConstructor.ts(20,9): error TS18064: A 'use strict' directive must be at the top of a function body.
 strictModeInConstructor.ts(27,5): error TS2376: A 'super' call must be the first statement in the constructor to refer to 'super' or 'this' when a derived class contains initialized properties, parameter properties, or private identifiers.
 strictModeInConstructor.ts(29,17): error TS17009: 'super' must be called before accessing 'this' in the constructor of a derived class.
+strictModeInConstructor.ts(31,9): error TS18064: A 'use strict' directive must be at the top of a function body.
+strictModeInConstructor.ts(49,9): error TS18064: A 'use strict' directive must be at the top of a function body.
+strictModeInConstructor.ts(59,9): error TS18064: A 'use strict' directive must be at the top of a function body.
 
 
-==== strictModeInConstructor.ts (2 errors) ====
+==== strictModeInConstructor.ts (6 errors) ====
     class A {
     }
 
@@ -23,6 +27,8 @@ strictModeInConstructor.ts(29,17): error TS17009: 'super' must be called before
         constructor () {
             super();            // No error
             "use strict";
+            ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
         }
     }
 
@@ -38,6 +44,8 @@ strictModeInConstructor.ts(29,17): error TS17009: 'super' must be called before
 !!! error TS17009: 'super' must be called before accessing 'this' in the constructor of a derived class.
             super();
             "use strict";
+            ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
         }
     }
 
@@ -56,6 +64,8 @@ strictModeInConstructor.ts(29,17): error TS17009: 'super' must be called before
         constructor () {
             super();            // No error
             "use strict";
+            ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
         }
     }
 
@@ -66,5 +76,7 @@ strictModeInConstructor.ts(29,17): error TS17009: 'super' must be called before
             var x = 1; // no Error
             super();
             "use strict";
+            ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
         }
     }

tsc/testdata/baselines/reference/compiler/useStrictNotInPrologue.errors.txt

@@ -0,0 +1,66 @@
+useStrictNotInPrologue.ts(3,5): error TS18064: A 'use strict' directive must be at the top of a function body.
+useStrictNotInPrologue.ts(9,5): error TS18064: A 'use strict' directive must be at the top of a function body.
+useStrictNotInPrologue.ts(20,5): error TS18064: A 'use strict' directive must be at the top of a function body.
+useStrictNotInPrologue.ts(25,5): error TS18064: A 'use strict' directive must be at the top of a function body.
+useStrictNotInPrologue.ts(31,9): error TS18064: A 'use strict' directive must be at the top of a function body.
+useStrictNotInPrologue.ts(37,9): error TS18064: A 'use strict' directive must be at the top of a function body.
+
+
+==== useStrictNotInPrologue.ts (6 errors) ====
+    function afterStatement() {
+        console.log("not strict");
+        "use strict";
+        ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
+    }
+
+    function afterDirectiveAndStatement() {
+        "use client";
+        console.log("not strict");
+        "use strict";
+        ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
+    }
+
+    function validDirective() {
+        "use client";
+        "use strict";
+        console.log("strict");
+    }
+
+    const arrow = () => {
+        console.log("not strict");
+        "use strict";
+        ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
+    };
+
+    function* generator() {
+        yield;
+        "use strict";
+        ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
+    }
+
+    class C {
+        method() {
+            console.log("not strict");
+            "use strict";
+            ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
+        }
+    }
+
+    function nestedBlock() {
+        if (true) {
+            "use strict";
+            ~~~~~~~~~~~~~
+!!! error TS18064: A 'use strict' directive must be at the top of a function body.
+        }
+    }
+
+    function afterTypeOnlyStatement() {
+        interface I {}
+        "use strict";
+    }
+

tsc/testdata/baselines/reference/compiler/useStrictNotInPrologue.js

@@ -0,0 +1,87 @@
+//// [tests/cases/compiler/useStrictNotInPrologue.ts] ////
+
+//// [useStrictNotInPrologue.ts]
+function afterStatement() {
+    console.log("not strict");
+    "use strict";
+}
+
+function afterDirectiveAndStatement() {
+    "use client";
+    console.log("not strict");
+    "use strict";
+}
+
+function validDirective() {
+    "use client";
+    "use strict";
+    console.log("strict");
+}
+
+const arrow = () => {
+    console.log("not strict");
+    "use strict";
+};
+
+function* generator() {
+    yield;
+    "use strict";
+}
+
+class C {
+    method() {
+        console.log("not strict");
+        "use strict";
+    }
+}
+
+function nestedBlock() {
+    if (true) {
+        "use strict";
+    }
+}
+
+function afterTypeOnlyStatement() {
+    interface I {}
+    "use strict";
+}
+
+
+//// [useStrictNotInPrologue.js]
+"use strict";
+function afterStatement() {
+    console.log("not strict");
+    "use strict";
+}
+function afterDirectiveAndStatement() {
+    "use client";
+    console.log("not strict");
+    "use strict";
+}
+function validDirective() {
+    "use client";
+    "use strict";
+    console.log("strict");
+}
+const arrow = () => {
+    console.log("not strict");
+    "use strict";
+};
+function* generator() {
+    yield;
+    "use strict";
+}
+class C {
+    method() {
+        console.log("not strict");
+        "use strict";
+    }
+}
+function nestedBlock() {
+    if (true) {
+        "use strict";
+    }
+}
+function afterTypeOnlyStatement() {
+    "use strict";
+}

tsc/testdata/baselines/reference/compiler/useStrictNotInPrologue.symbols

@@ -0,0 +1,87 @@
+//// [tests/cases/compiler/useStrictNotInPrologue.ts] ////
+
+=== useStrictNotInPrologue.ts ===
+function afterStatement() {
+>afterStatement : Symbol(afterStatement, Decl(useStrictNotInPrologue.ts, 0, 0))
+
+    console.log("not strict");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+
+    "use strict";
+}
+
+function afterDirectiveAndStatement() {
+>afterDirectiveAndStatement : Symbol(afterDirectiveAndStatement, Decl(useStrictNotInPrologue.ts, 3, 1))
+
+    "use client";
+    console.log("not strict");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+
+    "use strict";
+}
+
+function validDirective() {
+>validDirective : Symbol(validDirective, Decl(useStrictNotInPrologue.ts, 9, 1))
+
+    "use client";
+    "use strict";
+    console.log("strict");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+}
+
+const arrow = () => {
+>arrow : Symbol(arrow, Decl(useStrictNotInPrologue.ts, 17, 5))
+
+    console.log("not strict");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+
+    "use strict";
+};
+
+function* generator() {
+>generator : Symbol(generator, Decl(useStrictNotInPrologue.ts, 20, 2))
+
+    yield;
+    "use strict";
+}
+
+class C {
+>C : Symbol(C, Decl(useStrictNotInPrologue.ts, 25, 1))
+
+    method() {
+>method : Symbol(C.method, Decl(useStrictNotInPrologue.ts, 27, 9))
+
+        console.log("not strict");
+>console.log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+>console : Symbol(console, Decl(lib.dom.d.ts, --, --))
+>log : Symbol(Console.log, Decl(lib.dom.d.ts, --, --))
+
+        "use strict";
+    }
+}
+
+function nestedBlock() {
+>nestedBlock : Symbol(nestedBlock, Decl(useStrictNotInPrologue.ts, 32, 1))
+
+    if (true) {
+        "use strict";
+    }
+}
+
+function afterTypeOnlyStatement() {
+>afterTypeOnlyStatement : Symbol(afterTypeOnlyStatement, Decl(useStrictNotInPrologue.ts, 38, 1))
+
+    interface I {}
+>I : Symbol(I, Decl(useStrictNotInPrologue.ts, 40, 35))
+
+    "use strict";
+}
+