Introduction

I would disagree with the claim that Perforce integration in Visual Studio is "terrible". Rather, I'd define it as "out of the box experience is less than optimal" :-). The following sections discuss my understanding of the integration and recommendations for project/solution setup.

If you're not interested in the details of how the source control integration works you can skip to the end of this answer where I summarize answers to Weeble's question.

Disclaimer: The following sections are just educated guesses based on my empirical experience, however I've used the technique over many years in many projects (each project having multiple experimental/trunk/maintenance/release branches, sometimes even multiple solution files, without issues). The disadvantage is that you have to manually update the project files - but the 2 minute investment is amortized over the lifetime of a project pretty nicely IMHO :-).

Solution vs. Project

Visual Studio uses source control binding information from both solution file and each project file during the initial solution loading. This binding information is then stored in name.suo file (assuming we're using name.sln as solution) - note that suo files are marked with hidden flag so they won't be visible in file explorer (unless you override the "Hidden files and folders" option).

The easiest way to re-bind to source control provider if anything goes wrong is to delete the appropriate suo file and reopen solution. After suo file has been created, changes to <Scc*> elements have no effect.

If during the initial solution opening there is a discrepancy between the binding information stored in solution file and information stored in project file, Visual Studio will attempt to fix this (sometimes it will even prompt for your decision to choose whether the information in solution or the information in project should be used as a "master" to resolve the discrepancy):

Why is Visual Studio violating DRY (Don't Repeat Yourself) principle? I have no idea. I presume this has historic reasons and is tightly coupled to the needs of that nightmare called Visual Source Safe :-).

How to set it up "correctly"?

When adding either new or existing solutions/projects to Perforce, I always start by creating a blank solution (see the "Source-controlling a blank solution" section). I then add projects to this blank solution, one after another. The steps differ slightly based on whether the project being added already exists (see the "Source-controlling existing (unbound) projects" and "Source-controlling existing (bound) projects" sections) or I need to create a new one (see the "Source-controlling new projects" section).

Source-controlling a blank solution

To add a new blank solution to source control, do the following:

1. Start Visual Studio, "New" -> "Project..." -> "Other project types" -> "Blank solution"; fill in solution name and location, "OK" button
2. "File" -> "Source Control" -> "Add Solution to Source Control..."
3. In the connection dialog enter appropriate P4 server port, client and user (note that view of the selected client must include the location that you picked in step 1)
4. "View" -> "Pending Checkins" -> "Check In" -> in the submit dialog instead of hitting the "Submit" button, use "Cancel".
   Reason: The "Check In" action will create a new file, "name.vssscc", then add both "name.sln" and "name.vssscc" to Perforce's default changelist; by cancelling the submit dialog we will keep the "add" operation pending and will be able to edit the files before submitting to P4
5. Close Visual Studio

6. Open the name.sln file in your favourite editor (notepad, if you're really desperate :-) ) and add two new lines (SccProjectName0 and SccProvider0) - the blank solution file should now have a source control section as follows:

   GlobalSection(SourceCodeControl) = preSolution
       SccNumberOfProjects = 1
       SccLocalPath0 = .
       SccProjectName0 = Tutorial
       SccProvider0 = MSSCCI:Perforce\u0020SCM
   EndGlobalSection
   

   The values should be chosen as follows:

   • SccProjectName0: an arbitrary string that will be displayed in "Change Source Control" dialog as "Server Binding". This name is used to determine what projects/solution files can share the same source control connection. I recommend not using space for this name as escaping rules for spaces are different in solution and project files.
   • SccProvider0: hard-coded value "MSSCCI:Perforce\u0020SCM".
7. Submit the two pending files using the Perforce client of your choice (p4.exe, P4Win, P4V)

You can now test the bindings:

1. Make sure Visual Studio is closed
2. Delete **all* files except the name.sln (especially the name.suo)
3. Open Visual Studio and use it to open name.sln
4. A connection dialog should appear, use appropriate port/client/user and click OK
5. Solution explorer should now display the solution node with a padlock overlay icon:
6. You can now verify source control status of the solution by using "File" -> "Source Control" -> "Change Source Control...": Note: The column "Server Binding" is showing the value we chose for "SccProjectName0".

Source-controlling new projects

If you're creating a brand-new project and would like to immediately start tracking it in a Perforce depot, follow these steps:

1. Open the source-controlled solution in Visual Studio
2. "File" -> "Add" -> "New Project..." - pick the project type you're adding, name and location (location should be a subdirectory of the directory where the solution file is stored)
3. "File" -> "Save All" (this will commit all in-memory changes to solution file and the newly created project file to the disk)

4. Manually edit the project file you just created using an editor of your choice (come on, notepad AGAIN? ;-) ). Add the following property elements into a PropertyGroup (any property group):

   <PropertyGroup>
       ...
       <SccProjectName>Tutorial</SccProjectName>
       <SccLocalPath>..\..</SccLocalPath>
       <SccProvider>MSSCCI:Perforce SCM</SccProvider>
       ...
   </PropertyGroup>
   

   The values should be chosen as follows:

   • SccProjectName - this is the value that is displayed in "Change Source Control" dialog as "Server Binding"; should be the same as the value you used for SccProjectName0 in blank solution; if not the same, solution and this project won't be able to share the same source control provider connection
   • SccLocalPath - relative path to the reference directory (displayed in "Change Source Control" dialog as "Local binding"); because I recommend using the solution directory as the reference directory, this is in effect relative path from directory containing project file to directory containing solution file (my example is storing projects in "(solutionDir)/Source/ProjectName/projectName.csproj", thus the relative path is "two levels up")
   • SccProvider - hard-coded value "MSSCCI:Perforce SCM"; this is used to determine what SCCAPI provider are the Scc* binding values valid for

5. Switch back to Visual Studio; it should automatically detect that the project file has been updated externally and offer to reload it (if not, unload and reload the project manually)

6. "View" -> "Pending Checkins"
7. "Check In" -> I recommend right-clicking on (solutionName).vssscc file and selecting "Revert if unchanged" (even though Visual Studio opens it for edit, it remains unchanged); provide description and submit the change

To verify that the newly added project is bound properly, you can follow these steps:

1. Make sure Visual Studio is closed
2. Delete (solutionName).suo file as well as MSSCCPRJ.SCC (in solution directory)
3. Open Visual Studio and use it to open (solutionName).sln
4. A connection dialog should appear, use appropriate port/client/user and click OK
5. Solution explorer should now display the project node with a padlock overlay icon:

6. You can now verify source control status of the solution by using "File" -> "Source Control" -> "Change Source Control...":

   One thing to note about this status screenshot is that when I selected the solution row, all the remaining rows were "selected" as well (blue highlight). This is because all those entries have the same "Server Binding" + "Local Binding" and thus share the same source-control-provider (P4) connection.

   Also note that "Relative Path" for both projects has two levels, and are relative to the same "Local Binding" - the directory where solution file resides.

Source-controlling existing (unbound) projects

If you have existing projects that have not yet been used in any other Perforce solution, follow these steps to add them to Perforce (i.e. importing projects that have not been source-controlled before (Internet downloads etc.) or were using a different source control provider (Visual Source Safe, etc.).

1. Copy the project into appropriate location
2. Clean-up existing source control bindings (if any):
   • Remove existing project-file bindings, i.e. all properties starting with "Scc"
   • Delete file (projectName).vspscc in the same directory as the project file (if any)
3. Open the source-controlled solution in Visual Studio
4. "File" -> "Add" -> "Existing project..." - browse to the project (the copy you created in step 1)
5. "File" -> "Save All" (this will commit all in-memory changes to solution file)
6. Follow the steps 4-7 from "Source-controlling new projects" (i.e. you will now add "Scc*" property elements into a PropertyGroup)

Verification steps are exactly the same as in "Source-controlling new projects" section.

Source-controlling existing (bound) projects

If you have projects that have already been bound to Perforce using the technique discussed here and you want to use them in a different solution (new branch, alternative solution reusing the project, etc) use the following steps:

1. Integrate the project into desired location
2. Open the source-controlled solution in Visual Studio
3. "File" -> "Add" -> "Existing project..." - browse to the project created in step 1 via integration
4. "View" -> "Pending Checkins" -> "Check In" - add description and submit

Summary

• Source control binding information is stored in both solution and projects, must be in sync (if not, Visual Studio will attempt to fix any discrepancies)
• I always treat project files as the primary source of binding information and solution files as throwaway files that can be recreated easily by first source-controlling a blank solution and then adding desired projects
• Solution file should always have valid SccProvider0 and SccProjectName0 values (have to be added manually with new versions of P4SCC plugins)
• Project files should always have valid SccProjectName (preferrably same as SccProjectName0), SccLocalPath and SccProvider values (also have to be edited manually as the P4SCC defaults are no good)

I'm also including answers to your original questions:

What happens when you do "Change source control" and bind projects? How does Visual Studio decide what to put in the project and solution files?

This updates "Scc*" elements in a project file you're rebinding; the solution file is then updated as well so that it is in sync with the project file bindings

What happens when you do "Open from source control"?

Allows you to pick solution that you'd like to open. Afterwards all the projects included in the solution are automatically synced to head. I find this feature not very useful in Perforce world where you have to create a client anyway and the chances are you're syncing this client from a P4V/P4Win/P4 instead of relying on Visual Studio. This was kind-of useful in Visual Source Safe world where there was no concept of views and you were defining where a repository goes on checkout time.

What's this "connection" folder that SccLocalPath and SccProjectFilePathRelativizedFromConnection refer to? How does Visual Studio/Perforce pick it?

This is Visual Studio's bookkeeping. It is determined based on bindings in each project file (I guess in theory if a project file loses binding information for some reason, it could be reconstructed from the solution information...)

Is there some recommended way to make the source control bindings continue to work even when you create a new branch of the solution?

I hope the sections above give you some idea of a way that is working very well for me :-).

.dsp - Obsolete
.dsw - Obsolete
.ncb - for intellisense (should not be in source control)
.sln - Solution
.suo - Solution user options (should not be in source control)
.vcproj - VC++ project file
.vcproj.$DOMAIN.$USER.user - Project user options (should not be in source control)
.vcproj.vspscc - source control file
.vsscc - source control file
.vssscc - source control file

VSS = Visual Source Safe
SCC = Source Code Control (The TLA for the source control plugin architecture in VS)