Fix trailing line comment classified as enclosed in validators

.changeset/tidy-carrots-repair.md

@@ -0,0 +1,7 @@
+---
+"htmljs-parser": patch
+---
+
+Fix `isValidAttrValue` (and `isValidStatement` / `isValidScriptlet`) reporting `enclosed` for a value that ends in a trailing `//` line comment (e.g. `"hello" // note`).
+
+A line comment with no terminating newline consumes everything that would follow it on the line, so such a value is not safe to emit verbatim. It is now classified as `valid` (needs wrapping when placed inline), matching the existing behavior for an unguarded trailing newline. A comment guarded by a group (e.g. `("hello" // c\n)`) or a self-closing block comment (`"hello" /* c */`) still classifies as `enclosed`.

src/__tests__/validate.test.ts

@@ -124,5 +124,35 @@ describe("validation helpers", () => {
     it("rejects keyword operator with no operand", () => {
       assert.equal(isValidAttrValue("a as ", true), 0);
     });
+
+    it("treats a trailing line comment as unguarded", () => {
+      assert.equal(isValidAttrValue('"hello" // c', false), 1);
+      assert.equal(isValidAttrValue('"hello" // c', true), 1);
+      assert.equal(isValidAttrValue("foo // c", false), 1);
+      assert.equal(isValidAttrValue("1 + 2 // c", false), 1);
+      assert.equal(isValidAttrValue('"hello" /* c */ // d', false), 1);
+    });
+
+    it("keeps a self-closing block comment enclosed", () => {
+      assert.equal(isValidAttrValue('"hello" /* c */', false), 2);
+    });
+
+    it("keeps a line comment guarded by a group enclosed", () => {
+      assert.equal(isValidAttrValue('("hello" // c\n)', false), 2);
+    });
+
+    it("treats a newline after a value as unguarded", () => {
+      assert.equal(isValidAttrValue('"hello"\n// c', false), 1);
+    });
+  });
+
+  describe("trailing line comments", () => {
+    it("downgrades statements with a trailing line comment", () => {
+      assert.equal(isValidStatement("foo // c"), 1);
+    });
+
+    it("downgrades scriptlets with a trailing line comment", () => {
+      assert.equal(isValidScriptlet("foo // c"), 1);
+    });
   });
 });

src/states/EXPRESSION.ts

@@ -385,6 +385,15 @@ export const EXPRESSION: StateDefinition<ExpressionMeta> = {
   return(child, expression) {
     if (child.state === STATE.JS_COMMENT_LINE) {
       expression.wasComment = true;
+      // A line comment that runs to the end of the input (rather than being
+      // terminated by a newline or a closing tag) consumes everything that
+      // would follow it on the line, exactly like an unguarded newline. Flag
+      // it as unguarded so the value is not classified as `enclosed` (safe to
+      // inline verbatim) by the validation helpers — otherwise emitting it
+      // bare would comment out whatever comes next.
+      if (this.pos === this.maxPos && !expression.groupStack.length) {
+        expression.hadUnguardedNewline = true;
+      }
     }
   },
 };