Fix issue where datetimeformat is off by one due to GMT dates.

.github/workflows/build.yaml

@@ -22,7 +22,7 @@ jobs:
 
       - uses: actions/setup-node@v2
         with:
-          node-version: "20"
+          node-version: lts/*
 
       - name: Install NPM
         run: |
@@ -51,7 +51,7 @@ jobs:
 
       - uses: actions/setup-node@v2
         with:
-          node-version: "20"
+          node-version: lts/*
 
       - name: Install NPM
         run: |

.github/workflows/pr_build.yaml

@@ -1,9 +1,13 @@
 name: PR Build
 
+# `pull_request`, not `pull_request_target`. The latter reads its workflow definition and its
+# checkout from the base branch, so changes to this file only take effect after merging to main,
+# and the job tests main rather than the pull request's code. Forks get no secrets and cannot run
+# this, which is correct.
 on:
-  pull_request_target:
+  pull_request:
     branches: [ main ]
-    types: [ opened, reopened, synchronize, closed ]
+    types: [ opened, reopened, synchronize ]
 
 concurrency:
   group: ${{ github.ref }}
@@ -17,7 +21,7 @@ jobs:
 
       - uses: actions/setup-node@v2
         with:
-          node-version: "20"
+          node-version: "22.14.0"
 
       - name: Install dependencies
         run: npm install
@@ -52,4 +56,5 @@ jobs:
           fi
 
       - name: Clean up scratch org
+        if: always()
         run: sf org scratch delete --target-org=scratch-org --no-prompt

docs/src/app/docs/functions/page.md

@@ -454,9 +454,9 @@ DATETIME(2020, 1, 1, 12, 0, 0) // 2020-01-01 12:00:00
 
 ### DATETIMEFORMAT
 
-Formats a DateTime into a string using the provided format.
+Formats a Date or DateTime into a string using the provided format.
 
-Accepts 2 arguments: the DateTime to format and the format string.
+Accepts 2 arguments: the Date or DateTime to format and the format string.
 
 ```
 DATETIMEFORMAT(DATETIMEVALUE("2020-01-01 12:00:00"), "yyyy-MM-dd") // 2020-01-01

expression-src/main/editor/lwc/functions/functions-src.js

@@ -411,7 +411,7 @@ export const data = [
       {
         "name": "DATETIMEFORMAT",
         "autoCompleteValue": "DATETIMEFORMAT(",
-        "description": "Formats a DateTime into a string using the provided format.<br/><br/>Accepts 2 arguments: the DateTime to format and the format string.",
+        "description": "Formats a Date or DateTime into a string using the provided format.<br/><br/>Accepts 2 arguments: the Date or DateTime to format and the format string.",
         "examples": [
           "DATETIMEFORMAT(DATETIMEVALUE(\"2020-01-01 12:00:00\"), \"yyyy-MM-dd\") // 2020-01-01"
         ],

expression-src/main/src/interpreter/std-lib/DateAndTimeFunctions.cls

@@ -45,6 +45,12 @@ public with sharing class DateAndTimeFunctions {
         MILLISECOND, MINUTE, SECOND, HOUR_FN
     }
 
+    // A bare Date carries no time or timezone, so anchor it at GMT midnight. Callers must read it
+    // back in GMT (formatGmt/getTime) or the calendar day shifts for users west of GMT.
+    private static Datetime gmtMidnight(Date value) {
+        return Datetime.newInstanceGmt(value, Time.newInstance(0, 0, 0, 0));
+    }
+
     /**
      * @description Returns a date that is a specified number of days before or after a given date.
      *
@@ -591,7 +597,7 @@ public with sharing class DateAndTimeFunctions {
                 );
             }
 
-            return Integer.valueOf(Datetime.newInstanceGmt((Date)dateValue, Time.newInstance(0, 0, 0, 0)).format('Y'));
+            return Integer.valueOf(gmtMidnight((Date)dateValue).format('Y'));
         }
 
         public override Arity getArity() {
@@ -673,7 +679,7 @@ public with sharing class DateAndTimeFunctions {
 
             if (dateOrDateTimeOrTime instanceof Date) {
                 // Convert to datetime first
-                Datetime gmtDatetime = Datetime.newInstanceGmt((Date)dateOrDateTimeOrTime, Time.newInstance(0, 0, 0, 0));
+                Datetime gmtDatetime = gmtMidnight((Date)dateOrDateTimeOrTime);
                 return gmtDatetime.getTime() / 1000;
             } else if (dateOrDateTimeOrTime instanceof Datetime) {
                 Datetime gmtDateTime = Datetime.newInstanceGmt(((Datetime)dateOrDateTimeOrTime).date(), ((Datetime)dateOrDateTimeOrTime).time());
@@ -707,16 +713,7 @@ public with sharing class DateAndTimeFunctions {
                 );
             }
 
-            Date dateObj = (Date)dateValue;
-
-            return Integer.valueOf(Datetime.newInstanceGmt(
-                dateObj.year(),
-                dateObj.month(),
-                dateObj.day(),
-                0,
-                0,
-                0
-            ).format('u'));
+            return Integer.valueOf(gmtMidnight((Date)dateValue).format('u'));
         }
 
         public override Arity getArity() {
@@ -821,31 +818,37 @@ public with sharing class DateAndTimeFunctions {
     }
 
     /**
-     * @description Formats a DateTime into a string using the provided format.
+     * @description Formats a Date or DateTime into a string using the provided format.
      *
-     * Accepts 2 arguments: the DateTime to format and the format string.
+     * Accepts 2 arguments: the Date or DateTime to format and the format string.
      * @function DATETIMEFORMAT
      * @example
      * DATETIMEFORMAT(DATETIMEVALUE("2020-01-01 12:00:00"), "yyyy-MM-dd") // 2020-01-01
      */
     private class DateTimeFormatFn extends StandardFunction {
         public override Object call(List<Expr> arguments) {
-            // Expect a DateTime
+            // A Date also passes `instanceof Datetime` in Apex, so check for Date first.
             Object dateTimeValue = evaluate(arguments.get(0));
-            if (!(dateTimeValue instanceof Datetime)) {
+            Boolean isDate = dateTimeValue instanceof Date;
+            if (!isDate && !(dateTimeValue instanceof Datetime)) {
                 throw new FunctionExecutionException(
-                    'Error executing "DATETIMEFORMAT" function: the argument must evaluate to a datetime value.'
+                    'Error executing "DATETIMEFORMAT" function: the first argument must evaluate to a date or datetime value.'
                 );
             }
 
             // Expect a format string
             Object formatValue = evaluate(arguments.get(1));
             if (!(formatValue instanceof String)) {
                 throw new FunctionExecutionException(
-                    'Error executing "DATETIMEFORMAT" function: the argument must evaluate to a string value.'
+                    'Error executing "DATETIMEFORMAT" function: the second argument must evaluate to a string value.'
                 );
             }
 
+            if (isDate) {
+                // Format in GMT to match the anchor, so the calendar day is rendered as-is.
+                return gmtMidnight((Date)dateTimeValue).formatGmt((String)formatValue);
+            }
+
             return ((Datetime)dateTimeValue).format((String)formatValue);
         }
 

expression-src/spec/language/std-functions/DateAndTimeFunctionsTest.cls

@@ -225,6 +225,11 @@ private class DateAndTimeFunctionsTest {
         Assert.areEqual('2015-01-01 01:00:00', result);
     }
 
+    @IsTest
+    private static void dateTimeFormatFormatsADateWithoutShiftingTheDay() {
+        Assert.areEqual('2026-09-09', Evaluator.run('DATETIMEFORMAT(DATE(2026, 9, 9), "yyyy-MM-dd")'));
+    }
+
     @IsTest
     private static void dateToDateTimeConvertsADateToADateTime() {
         String formula = 'DATETODATETIME(DATEVALUE("2015-01-01"))';