[[DOCS]] Improve warning message for W040 (#3052)

Expand the message to describe the rationale for the warning.

src/messages.js

@@ -119,7 +119,8 @@ var warnings = {
   W037: "'{a}' is a statement label.",
   W038: "'{a}' used out of scope.",
   W039: "'{a}' is not allowed.",
-  W040: "Possible strict violation.",
+  W040: "If a strict mode function is executed using function invocation, " +
+    "its 'this' value will be undefined.",
   W041: "Use '{a}' to compare with '{b}'.",
   W042: "Avoid EOL escaping.",
   W043: "Bad escaping of EOL. Use option multistr if needed.",

tests/regression/thirdparty.js

@@ -152,7 +152,7 @@ exports.lodash_0_6_1 = function (test) {
   };
 
   TestRun(test)
-    .addError(168, "Possible strict violation.")
+    .addError(168, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .addError(170, "Missing '()' invoking a constructor.")
     .addError(632, "Missing semicolon.")
     .addError(920, "Reassignment of 'isArguments', which is is a function. Use 'var' or 'let' to declare bindings that may change.")
@@ -164,15 +164,15 @@ exports.lodash_0_6_1 = function (test) {
     .addError(1159, "'isArr' used out of scope.")
     .addError(1490, "Use '===' to compare with '0'.")
     .addError(1670, "Missing semicolon.")
-    .addError(3374, "Possible strict violation.")
+    .addError(3374, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .addError(3377, "Missing '()' invoking a constructor.")
     .addError(3384, "Missing semicolon.")
     .addError(3677, "Missing '()' invoking a constructor.")
     .addError(3683, "Missing '()' invoking a constructor.")
-    .addError(3825, "Possible strict violation.")
-    .addError(4225, "Possible strict violation.")
-    .addError(4226, "Possible strict violation.")
-    .addError(4242, "Possible strict violation.")
+    .addError(3825, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
+    .addError(4225, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
+    .addError(4226, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
+    .addError(4242, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(src, options, globals);
 
   test.done();

tests/unit/options.js

@@ -1705,7 +1705,7 @@ exports.strict = function (test) {
 
   // Test for strict mode violations
   run = TestRun(test)
-    .addError(4, 'Possible strict violation.')
+    .addError(4, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .addError(7, 'Strict violation.')
     .addError(8, 'Strict violation.');
   run.test(src, { es3: true, strict: true });
@@ -1992,9 +1992,9 @@ exports.validthis = function (test) {
   var src = fs.readFileSync(__dirname + '/fixtures/strict_this.js', 'utf8');
 
   TestRun(test)
-    .addError(8, "Possible strict violation.")
-    .addError(9, "Possible strict violation.")
-    .addError(11, "Possible strict violation.")
+    .addError(8, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
+    .addError(9, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
+    .addError(11, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(src, {es3: true});
 
   src = fs.readFileSync(__dirname + '/fixtures/strict_this2.js', 'utf8');
@@ -3596,12 +3596,12 @@ exports.module.behavior = function(test) {
   TestRun(test)
     .addError(0, "The 'module' option is only available when linting ECMAScript 6 code.")
     .addError(1, "Expected an identifier and instead saw 'package' (a reserved word).")
-    .addError(2, "Possible strict violation.")
+    .addError(2, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(code, { module: true });
 
   TestRun(test)
     .addError(1, "Expected an identifier and instead saw 'package' (a reserved word).")
-    .addError(2, "Possible strict violation.")
+    .addError(2, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(code, { module: true, esnext: true });
 
   code = [
@@ -3613,14 +3613,14 @@ exports.module.behavior = function(test) {
   TestRun(test)
     .addError(1, "The 'module' option is only available when linting ECMAScript 6 code.")
     .addError(2, "Expected an identifier and instead saw 'package' (a reserved word).")
-    .addError(3, "Possible strict violation.")
+    .addError(3, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(code);
 
   code[0] = "/* jshint module: true, esnext: true */";
 
   TestRun(test)
     .addError(2, "Expected an identifier and instead saw 'package' (a reserved word).")
-    .addError(3, "Possible strict violation.")
+    .addError(3, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(code);
 
   test.done();

tests/unit/parser.js

@@ -6126,7 +6126,7 @@ exports["class method this"] = function (test) {
   ];
 
   TestRun(test)
-    .addError(10, "Possible strict violation.")
+    .addError(10, "If a strict mode function is executed using function invocation, its 'this' value will be undefined.")
     .test(code, {esnext: true});
 
   test.done();