Return Invalid DateTime for using meridiem with 24-hour (#1549)

src/datetime.js

@@ -901,9 +901,13 @@ export default class DateTime {
         numberingSystem,
         defaultToEN: true,
       }),
-      [vals, parsedZone, specificOffset, invalid] = parseFromTokens(localeToUse, text, fmt);
+      [vals, parsedZone, specificOffset, invalid, explanation] = parseFromTokens(
+        localeToUse,
+        text,
+        fmt
+      );
     if (invalid) {
-      return DateTime.invalid(invalid);
+      return DateTime.invalid(invalid, explanation);
     } else {
       return parseDataToDateTime(vals, parsedZone, opts, `format ${fmt}`, text, specificOffset);
     }

src/impl/tokenParser.js

@@ -450,14 +450,30 @@ export function explainFromTokens(locale, input, format) {
       throw new ConflictingSpecificationError(
         "Can't include meridiem when specifying 24-hour format"
       );
+    } else if (
+      hasOwnProperty(matches, "h") &&
+      matches["h"] > 12 &&
+      tokens.find((t) => t.val === "h" || t.val === "hh")
+    ) {
+      const hourValue = matches["h"];
+      return {
+        input,
+        tokens,
+        invalidReason: "unit out of range",
+        invalidExplanation: `you specified ${hourValue} (of type ${typeof hourValue}) as an hour along with a meridiem, which is invalid`,
+      };
     }
     return { input, tokens, regex, rawMatches, matches, result, zone, specificOffset };
   }
 }
 
 export function parseFromTokens(locale, input, format) {
-  const { result, zone, specificOffset, invalidReason } = explainFromTokens(locale, input, format);
-  return [result, zone, specificOffset, invalidReason];
+  const { result, zone, specificOffset, invalidReason, invalidExplanation } = explainFromTokens(
+    locale,
+    input,
+    format
+  );
+  return [result, zone, specificOffset, invalidReason, invalidExplanation];
 }
 
 export function formatOptsToTokens(formatOpts, locale) {

test/datetime/tokenParse.test.js

@@ -18,10 +18,40 @@ test("DateTime.fromFormat() parses basic times", () => {
   expect(i.millisecond).toBe(445);
 });
 
+test("DateTime.fromFormat() yields Invalid reason for invalid 12-hour time", () => {
+  const i = DateTime.fromFormat("11-08-2023 15:00 AM", "MM-dd-yyyy h:mm a");
+  expect(i.invalid).not.toBeNull();
+  expect(i.invalid.reason).toEqual("unit out of range");
+  expect(i.invalid.explanation).toEqual(
+    "you specified 15 (of type number) as an hour along with a meridiem, which is invalid"
+  );
+});
+
+test("DateTime.fromFormat() yields Invalid reason for invalid 12-hour time with padding", () => {
+  const i = DateTime.fromFormat("11-08-2023 15:00 AM", "MM-dd-yyyy hh:mm a");
+  expect(i.invalid).not.toBeNull();
+  expect(i.invalid.reason).toEqual("unit out of range");
+  expect(i.invalid.explanation).toEqual(
+    "you specified 15 (of type number) as an hour along with a meridiem, which is invalid"
+  );
+});
+
+test("DateTime.fromFormat() throws ConflictingSpecificationError for invalid format", () => {
+  expect(() => {
+    DateTime.fromFormat("11-08-2023 12:00 AM", "MM-dd-yyyy H:mm a");
+  }).toThrowError(
+    ConflictingSpecificationError,
+    "Can't include meridiem when specifying 24-hour format"
+  );
+});
+
 test("DateTime.fromFormat() yields Invalid reason 'unparseable' for incompatible formats", () => {
   const i = DateTime.fromFormat("Mar 3, 2020", "MMM dd, yyyy");
-  expect(i.invalid).not.toBeNull;
+  expect(i.invalid).not.toBeNull();
   expect(i.invalid.reason).toEqual("unparsable");
+  expect(i.invalid.explanation).toEqual(
+    'the input "Mar 3, 2020" can\'t be parsed as format MMM dd, yyyy'
+  );
 });
 
 test("DateTime.fromFormat() parses with variable-length input", () => {