Fix custom Windows install directory display

build/installer.nsh

@@ -5,53 +5,107 @@
 
     Var DshDirectoryPage
     Var DshDirectoryEdit
+    Var DshDirectorySearchAfter
+    Var DshDirectoryAttached
     Var DshDirectoryNormalizationActive
 
-    ; MUI invokes this after the assisted installer's directory page is ready.
-    ; Normalize a selected drive root immediately so the page does not reject it
-    ; before electron-builder's later install-time sanitization can run.
+    ; electron-builder declares its install-mode page before the directory page.
+    ; MUI consumes this callback on that first page, so use it to start a short
+    ; polling timer and attach to the directory edit control once that page exists.
     !define MUI_PAGE_CUSTOMFUNCTION_SHOW DshDirectoryPageShow
 
     Function DshDirectoryPageShow
-      FindWindow $DshDirectoryPage "#32770" "" $HWNDPARENT
+      ${NSD_CreateTimer} DshAttachDirectoryPage 50
+    FunctionEnd
+
+    Function DshAttachDirectoryPage
+      ${If} $DshDirectoryAttached == "1"
+        System::Call 'USER32::IsWindowVisible(p $DshDirectoryPage)i.r0'
+        ${If} $0 == 0
+          ; The user can navigate back to the install-mode page and then return.
+          ; Keep the timer alive so the directory page can be attached again.
+          StrCpy $DshDirectoryAttached "0"
+          StrCpy $DshDirectoryPage 0
+          StrCpy $DshDirectoryEdit 0
+        ${Else}
+          ; Keep polling while the directory page is visible. This also catches a
+          ; manually entered parent path as soon as the edit control loses focus.
+          Call DshNormalizeSelectedDirectory
+          Return
+        ${EndIf}
+      ${EndIf}
+
+      StrCpy $DshDirectorySearchAfter 0
+
+      DshFindDirectoryPage:
+      FindWindow $DshDirectoryPage "#32770" "" $HWNDPARENT $DshDirectorySearchAfter
+
+      ${If} $DshDirectoryPage == 0
+        Return
+      ${EndIf}
+
       GetDlgItem $DshDirectoryEdit $DshDirectoryPage 1019
+
+      ${If} $DshDirectoryEdit == 0
+        ; MUI keeps earlier custom pages as hidden child dialogs. Continue until
+        ; the child containing the actual directory edit control is found.
+        StrCpy $DshDirectorySearchAfter $DshDirectoryPage
+        Goto DshFindDirectoryPage
+      ${EndIf}
+
+      System::Call 'USER32::IsWindowVisible(p $DshDirectoryPage)i.r0'
+      ${If} $0 == 0
+        StrCpy $DshDirectorySearchAfter $DshDirectoryPage
+        Goto DshFindDirectoryPage
+      ${EndIf}
+
       ${NSD_OnChange} $DshDirectoryEdit DshDirectoryChanged
-      Call DshNormalizeDriveRoot
+      StrCpy $DshDirectoryAttached "1"
+      Call DshNormalizeSelectedDirectory
     FunctionEnd
 
     Function DshDirectoryChanged
       Pop $0
-      Call DshNormalizeDriveRoot
+      Call DshNormalizeSelectedDirectory
     FunctionEnd
 
-    Function DshNormalizeDriveRoot
+    Function DshNormalizeSelectedDirectory
       ${If} $DshDirectoryNormalizationActive == "1"
         Return
       ${EndIf}
 
+      ; A Browse selection updates the edit while focus remains on the Browse
+      ; button. Do not rewrite the path character-by-character when the user is
+      ; typing directly into the edit control.
+      System::Call 'USER32::GetFocus()p.r4'
+      ${If} $4 == $DshDirectoryEdit
+        Return
+      ${EndIf}
+
       ${NSD_GetText} $DshDirectoryEdit $0
-      StrLen $1 $0
 
-      ; Accept both forms produced by typing or the Windows folder picker:
-      ; "D:" and "D:\". Any non-root directory is left untouched.
-      ${If} $1 == 2
-        StrCpy $2 $0 1 1
-        ${If} $2 != ":"
-          Return
-        ${EndIf}
-        StrCpy $3 "$0\${APP_FILENAME}"
-      ${ElseIf} $1 == 3
-        StrCpy $2 $0 1 1
-        ${If} $2 != ":"
-          Return
-        ${EndIf}
-        StrCpy $2 $0 1 2
-        ${If} $2 != "\"
+      ${If} $0 == ""
+        Return
+      ${EndIf}
+
+      ; Keep the default path and an already-normalized custom path unchanged.
+      StrLen $1 "${APP_FILENAME}"
+      StrLen $2 $0
+      ${If} $2 >= $1
+        IntOp $4 $2 - $1
+        StrCpy $3 $0 $1 $4
+        ${If} $3 == "${APP_FILENAME}"
           Return
         ${EndIf}
+      ${EndIf}
+
+      ; The directory picker returns the selected parent directory. Make the
+      ; application subdirectory visible immediately for every custom location.
+      StrCpy $1 $0 1 -1
+      ${If} $1 == "\"
         StrCpy $3 "$0${APP_FILENAME}"
       ${Else}
-        Return
+        StrCpy $3 "$0\${APP_FILENAME}"
       ${EndIf}
 
       StrCpy $DshDirectoryNormalizationActive "1"

test/release.test.ts

@@ -76,14 +76,25 @@ describe('GitHub release contract', () => {
     expect(packageJson.build.portable).toBeUndefined()
   })
 
-  it('turns a selected Windows drive root into an application directory', async () => {
+  it('shows the application subdirectory for every custom Windows install location', async () => {
     const installer = await readFile(
       path.join(projectRoot, 'build', 'installer.nsh'),
       'utf8'
     )
 
     expect(installer).toContain('!define MUI_PAGE_CUSTOMFUNCTION_SHOW DshDirectoryPageShow')
+    expect(installer).toContain('${NSD_CreateTimer} DshAttachDirectoryPage 50')
+    expect(installer).toContain(
+      'FindWindow $DshDirectoryPage "#32770" "" $HWNDPARENT $DshDirectorySearchAfter'
+    )
+    expect(installer).toContain('Goto DshFindDirectoryPage')
+    expect(installer).toContain('StrCpy $DshDirectoryAttached "0"')
     expect(installer).toContain('${NSD_OnChange} $DshDirectoryEdit DshDirectoryChanged')
+    expect(installer).toContain(
+      "System::Call 'USER32::IsWindowVisible(p $DshDirectoryPage)i.r0'"
+    )
+    expect(installer).toContain("System::Call 'USER32::GetFocus()p.r4'")
+    expect(installer).toContain('StrLen $1 "${APP_FILENAME}"')
     expect(installer).toContain('StrCpy $3 "$0\\${APP_FILENAME}"')
     expect(installer).toContain('StrCpy $3 "$0${APP_FILENAME}"')
     expect(installer).toContain('${NSD_SetText} $DshDirectoryEdit $3')