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Visual Studio 2022 not showing syntax errors and Intellisense is not working properly

Working on a project I made a class with properties and when I tried to auto-generate a class constructor I got an error saying something on lines of "auto generation of class constructor failed... and will be disabled" and ever sense then the "generate constructor" option has been taken off the Refactor menu and on top of that I don't get syntax error highlighting anymore and intellisense doesn't seem to be working proper or at all.
I tried using going into Tools > Options > Text Editor > various fields including "C#" and "general") and I don't see anything obviously wrong. I also tried to use Visual Studio Installer to try to repair and that didn't do anything. I am completely out of ideas and I can't find anything that is remotely close to my case. TIA

I can't add this reply as a comment as I don't have 50 reputation.
I created a .Net 6.0 C# console project in Visual Studio 2022, add a class, and add two private fields. Selecting these two fields, press Alt+Enter to quickly generate the constructor. I did not encounter your issue.
Please try:
Go to Visual Studio Installer, click Modify, uncheck IntelliCode in Individual components, then click Modify button to save the change, wait for the installation to complete, and then reinstall IntelliCode.
In Visual Studio, go to Tools->Options->IntelliCode to check if the setting is Default.

Go to Tools menu, and select Options. Under Intellicode select General. Just uncheck “C# Suggestions”. Then restart Visual Studio and check that intellisence and syntax errors are appearing.
Note, I was not able to figure out what this option does, as the C# code suggestions seemed to continue to work as expected.

Visual studio stuck cursor

In unity and visual studio , some of the scripts I am creating ,wont let me use shortcuts, cant write where I put the cursor, cant even use ctrl+F, this is new and really stopping my workflow. Have you got any workarounds for this bug?
When I type it seems like the place where all the words are typed from it is always the same and won't change no matter if I click on a different place in the script.
If I restart visual studio, the problem for those scripts will stop, but other scripts will have the same problem then.
I am using visual studio 17 15.9 and Unity 2018.3.b10
Thank you for your help

Ok, I found a workaround. My scripts in visual studio were coming up on the tabs with a 1 or 2 after the name of the script, like they were duplicates. The solution was to close them pressing x, then find them in the solution explorer, repeating this until that number was gone.
After this, that problem is gone.

Visual Studio doesn't show me the red squiggle Intellisense errors [duplicate]

My Visual Studio (2008) Editor has stopped to underline Errors (this nifty wavy red lines). I can't really tell when, but it can be related to the installation of .Net Framework 3.5 SP 1 or the MVC Beta (which I guess is unlikely). Furthermore have I installed and uninstalled both CodeRush and Resharper for evaluation purposes (decided not to keep either one of them).
Does anyone know the problem and how to restore this functionality again?

Have you checked Tools→Options...→Text Editor→C#→Advanced→Underline errors in the editor?
I usually like to reset my settings after messing around with plugins, as they tend to mess with settings: Tools→Import and Export Settings...→Reset all settings.

About possible causes.
For VS 2012 and 2013 if you have more than one instance of Visual Studio on different machines binded to one "live" account and have installed ReSharper on one of them, it disables the native IntelliSense and error underlines (to replace by it's own rules) that will be synchronised through your account to another machine without ReSharper.

Found it in Visual Studio 2019 as: Tools > Options > Text Editor > General > Show error squiggles

This is generally called Disable Squiggly or Wavy lines in Visual Studio.
How you will do in Visual studio 2013?
TOOLS -> Options... -> Text Editor -> C/C++ -> Advanced -> Disable Squiggles: True/False (Under IntelliSense) -> Press OK

I know its an old question, and with various solutions, but I have fixed it in different way. I'm working with Unity3D on my C# code using VS2017, when suddenly VS decides to stop underlining error while im typing. However, if I close the file tab and reopen, it suddenly undelines the error.
For example:
class A {
public int x;
s;
}
should obvsiouly give an error for that lonely 's' symbol. But, VS doesn't underline it until I close and reopen this file tab.
Solution:
Copied the entire Unity Project folder (which is like a regular VS Solution folder basically) and worked with the new folder, which issue was gone there.

For visual studio 2017 act according to HeeJae's comments in:
https://developercommunity.visualstudio.com/content/problem/113112/design-time-error-checking-isnt-working.html
i.e:
Hi. you are probably hitting a known issue. can you try this?
1.Update to latest release If that doesn’t solve it
2.Go to Tools\Options\Projects and Solutions\General and uncheck “Allow parallel project initialization”.
3.Close VS.
4.Delete the “.vs” directory beside their solution file.
5.Reopen VS.
..
thank you
You can re-enable the "Allow parallel project initialization" option after the issue was solved.
I tried to upgrade VS, reset VS settings, clear VS cache and everything people do conventionally but none of them solved this issue! At the end the mentioned solution worked for me magically.
Good luck

Unloading and loading same project again from the solution does the trick. Just right click on the project and click "Unload Project". Once unloaded, again right click the same project and click "Reload Project". Error highlighting will return.

I had the same issue with 2017. There was a 'disable intelisense' option, make sure that is set to false.

For everyone wondering in 2021..
search for "C_Cpp.errorSquiggles" in the settings.
Make sure to have it active for the user, as well as the workspace.
No need to restart Visual Studio.

For me (VS 2019) , after trying the other answers also, setting the scope of analysis from "Current document" to Open document" brought back the missing error markers

Just go to settings and search for errors and Image in Error Squiggles. You can see the Error squiggles (Modified: Workspace - Right now you can't see it because I modified it). Just click on modified and you will see the disabled option. If by mistake you disabled it, just enable it and you can see the red line errors again in your code.

In latest edition, check for .vscode folder in same project folder. There will be a setting.json file in that. Delete the key value pair of "C_Cpp.errorSquiggles": "Disabled". Restart the vs code.

Xamarin for Visual Studio 2015 Portable Forms need to "retouch" MainPAge.xaml to avoid errors

sorry if this questions been asked already, I suspect it's quite common..
I'm using Xamarin for Visual Studio 2015 (4.0.3.214), and a common thing is that every now and again after saving or loading the project all the variables associated with the MainPage.xaml file are red, i.e. showing up as errors in the solution error list.
By retouching - saving the file after an edit (like adding a space then doing a backspace so nothing changes), the errors go away.
Which suggests a problem with the way Xamarin handles the build process and keeps track of auto-generated files. Is there a solution or a fix to this, or even a proper explanation ?

Visual Studio C# IntelliSense not automatically displaying

Just recently, my Visual Studio 2010 stopped displaying IntelliSense suggestions automatically while I am typing. I can still press ctrl+space to get it to work, but it doesn't automatically show a list of suggestions like it used to. I have already tried disabling all my extensions, restarting VS and the computer, and I have checked all the appropriate settings (Options -> Text Editor -> C# -> IntelliSense) to make sure that it is set to offer suggestions after a character is typed.
Has anyone seen this behavior before? Does anyone have any other suggestions for how I can get IntelliSense to go back to the way things were before? If not, I might just have to do a fresh reinstall of VS...

In prose, in case you can't see the above image:
Open Tools > Options > Text Editor. If you're only having this issue with one language, find that language; if it's for everything, click "All Languages". Right at the top, there'll be a few options labeled "Auto list members", "Hide advanced members", and "Parameter information". Make sure all of those are enabled (though the second may be disabled; if so, ignore it).

I have found that at times even verifying the settings under Options --> Statement Completion (the answer above) doesn't work. In this case, saving and restarting Visual Studio will re-enable Intellisense.
Finally, this link has a list of other ways to troubleshoot Intellisense, broken down by language (for more specific errors).
http://msdn.microsoft.com/en-us/library/vstudio/ecfczya1(v=vs.100).aspx

I'll start off my noting that this hasn't happened since I upgraded my RAM. I was at 4GB and would often have multiple instances of VS open along with SSMS. I have since gone to 8GB and then 16GB.
Here's the steps I go through when I lose intellisense.
If only one file/window appears to be affected, close/reopen that file. If that doesn't work, try below.
In Visual Studio:
Click Tools->Options->Text Editor->All Languages->General
Uncheck "Auto list members"
Uncheck "Parameter information"
Check "Auto list members" (yes, the one you just unchecked)
Check "Parameter information" (again, the one you just unchecked)
Click OK
If this doesn't work, here's a few more steps to try:
Close all VS documents and reopen
If still not working, close/reopen solution
If still not working, restart VS.
For C++ projects:
MSDN has a few things to try: MSDN suggestions
The corrupt .ncb file seems most likely.
From MSDN:
Close the solution.
Delete the .ncb file.
Reopen the solution. (This creates a new .ncb file.)
Notes:
This issue does not appear to be specific to C# as C++ and VB users
report the same issue
Tested in VS 2013/2015

Steps to fix are:
Tools
Import and Export Settings
Reset all settings
Back up your config
Select your environment settings and finish

I also faced the same issue but in VS2013.
I did the below way to fix, It was worked fine.
Close all the opened Visual studio instance.
Then, go to "Developer command prompt" from visual studio tools,
Type it as devenv.exe /resetuserdata
Restart the machine, Open the Visual studio then It will ask you to choose the development settings from initial onwards, thereafter open any solution/project. You'll be amazed.
Hope, it might helps you :)

Deleted the .suo file in solution folder to solve the problem.

Sometimes i've found Intellisense to be slow. Hit the . and wait for a minute and see if it appears after a delay. If so, then I believe there may be a cache that can be deleted to get it to rescan.

I hit this today after the following sequence:
Added a new class to my project.
Closed Visual Studio, but accidentally selected No when it asked if I wanted to save changes.
Reopened Visual Studio, and found that it reopened the new file automatically but without my previous changes (as expected). However, IntelliSense was no longer working in the new file.
The problem was in addition to not saving changes to the new file, it didn't save changes to the project, so after reopening Visual Studio the file was not part of the project. The Show All Files command in Solution Explorer, or Add → Existing Item..., resolved the problem.

I had the file excluded from the project so i was not able to debug and have intellisense on that file.
Including the file back into the project solved my problem! :)

A new cause for this in the .net core era is having a project loaded for an unsupported .net core version. For instance if you loaded a project from GitHub that was set to use:
<PropertyGroup>
<TargetFramework>netcoreapp2.2</TargetFramework>
<AspNetCoreHostingModel>InProcess</AspNetCoreHostingModel>
</PropertyGroup>
But you only have 2.1 installed or find yourself using Visual Studio 2017 then the compiler wont be able to find the SDK code and thus provide intellisense.
The solution in that case might be to right click on your project and select Edit MyProject.csproj from the context menu and change the target framework as necessary:
<PropertyGroup>
<TargetFramework>netcoreapp2.1</TargetFramework>
<AspNetCoreHostingModel>InProcess</AspNetCoreHostingModel>
</PropertyGroup>
This assumes whatever project you loaded can actually be run under a lesser target framework.

I simply closed all pages of visual studio and reopened ..it worked.

Deleting the .vs folder in the solution solved my issue. You have to exit from Visual Studio and then delete the .vs folder and start Visual Studio again.

Closed all my VS windows
Started the Visual Studio Installer and clicked 'Modify'.
Under 'Individual components' > 'Code Tools' > Deselected NuGet package manager and re-selected it.
After modifying and restarting VS, IntelliSense was working correctly again.
Found my answer on https://developercommunity.visualstudio.com/content/problem/130597/unity-intellisense-not-working-after-creating-new-1.html

[Tools -> Options -> Text Editor -> All Languages -> CodeLens]
Check if check box "Enable CodeLens" is checked

I have just come to about this problem while installing one of the extensions and its file was deleted by my anti virus so I just disabled my anti virus and reinstalled visual studio. Suggestions are working properly without any changes made after installation.

At the bottommost right look at the blue line where Ln, Col, Spaces, UTF, CRLF,..... here the language is specified.
Check that your language and the language specified there are the same.
In my case, it was Django Python while I was trying to use HTML.

This may be due to the solution configuration changed to Release Mode instead of debug. Right click on solution -> Properties -> Configuration Properties -> Set Configuration To Debug if it is in Release.