[wasm] Fix "bump-chrome-pr.env" update. (#98480)

* Fix "bump-chrome-pr.env" update.

* Fix: do not overwrite the .env file (emptying it) when there was no update.

Author: ilonatommy

eng/testing/bump-chrome-version.proj

@@ -4,6 +4,7 @@
   <UsingTask AssemblyFile="$(WasmBuildTasksAssemblyPath)" TaskName="Microsoft.WebAssembly.Build.Tasks.UpdateChromeVersions" />
   <PropertyGroup>
     <ChromeVersionsPath>$(RepositoryEngineeringDir)testing\ChromeVersions.props</ChromeVersionsPath>
+    <EnvVarsForPRPath>$(RepositoryEngineeringDir)testing\bump-chrome-pr.env</EnvVarsForPRPath>
   </PropertyGroup>
 
   <Target Name="UpdateChromeVersion">
@@ -13,19 +14,13 @@
                 Channel="$(ChromeChannel)"
                 MaxMajorVersionsToCheck="1"
                 IntermediateOutputPath="$(ArtifactsObjDir)"
-                ChromeVersionsPath="$(ChromeVersionsPath)">                
+                ChromeVersionsPath="$(ChromeVersionsPath)"
+                EnvVarsForPRPath="$(EnvVarsForPRPath)">                
       <Output TaskParameter="VersionsChanged" PropertyName="VersionsChanged" />
     </UpdateChromeVersions>
 
-    <ItemGroup>
-      <!-- ensure newline at the end -->
-      <EnvVarForPR Include="CHROME_LINUX_VER=$(linux_ChromeVersion)" />
-      <EnvVarForPR Include="CHROME_WIN_VER=$(win_ChromeVersion)" />
-    </ItemGroup>
-
     <Message Text="No major changes: skipping version props update." Importance="High" Condition="'$(VersionsChanged)' != 'true'"/>
     <Message Text="Version props got updated" Importance="High" Condition="'$(VersionsChanged)' == 'true'"/>
-
   </Target>
 
   <Import Project="..\..\Directory.Build.targets" />

src/tasks/WasmBuildTasks/UpdateChromeVersions.cs

@@ -44,6 +44,9 @@ public partial class UpdateChromeVersions : MBU.Task
     [Required, NotNull]
     public string ChromeVersionsPath { get; set; } = string.Empty;
 
+    [Required, NotNull]
+    public string EnvVarsForPRPath { get; set; } = string.Empty;
+
     public int MaxMajorVersionsToCheck { get; set; } = 2;
 
     // start at the branch position found in all.json, and try to
@@ -70,15 +73,21 @@ private async Task<bool> ExecuteInternalAsync()
             XmlDocument chromeVersionsXmlDoc = new XmlDocument();
             chromeVersionsXmlDoc.Load(ChromeVersionsPath);
             var osInfo = OSIdentifiers.Zip(OSPrefixes, (num, str) => new { Identifier = num, Prefix = str });
+            List<ChromeVersionSpec> versions = new();
             foreach (var info in osInfo)
             {
                 (ChromeVersionSpec version, string baseUrl) = await FindVersionFromChromiumDash(info.Prefix, info.Identifier).ConfigureAwait(false);
+                versions.Add(version);
                 bool hasMajorChanges = AreVersionsChanged(chromeVersionsXmlDoc, version, baseUrl);
                 if (hasMajorChanges)
                 {
                     VersionsChanged = UpdateChromeVersionsFile(chromeVersionsXmlDoc, version, baseUrl);
                 }
             }
+            if (VersionsChanged)
+            {
+                UpdateEnvVarsForPRFile(versions);
+            }
             return !Log.HasLoggedErrors;
         }
         catch (LogAsErrorException laee)
@@ -137,6 +146,26 @@ private bool UpdateChromeVersionsFile(XmlDocument xmlDoc, ChromeVersionSpec vers
         return true;
     }
 
+    private void UpdateEnvVarsForPRFile(List<ChromeVersionSpec> versions)
+    {
+        using StreamWriter writer = new StreamWriter(EnvVarsForPRPath);
+        foreach (var version in versions)
+        {
+            if (string.Equals(version.os, "Linux", StringComparison.OrdinalIgnoreCase))
+            {
+                writer.WriteLine($"CHROME_LINUX_VER={version.version}");
+            }
+            else if (string.Equals(version.os, "Windows", StringComparison.OrdinalIgnoreCase))
+            {
+                writer.WriteLine($"CHROME_WIN_VER={version.version}");
+            }
+            else
+            {
+                throw new Exception($"UpdateEnvVarsForPRFile task was used with unknown OS: {version.os}");
+            }
+        }
+    }
+
     private static void UpdateNodeValue(XmlDocument xmlDoc, string nodeName, string newValue)
     {
         XmlNode? node = xmlDoc.SelectSingleNode($"/Project/PropertyGroup/{nodeName}");