[Docs] Add troubleshooting tips

README.md

@@ -404,12 +404,14 @@ Note: This setup is not recommended and may not be supported in future XCRemoteC
 * Recommended: multi-targets Xcode project
 * Recommended: do not use fast-forward PR strategy (use merge or squash instead)
 * Recommended: avoid `DWARF with dSYM File` "Debug Information Format" build setting. Use `DWARF` instead
+* Recommended: avoid having a symbolic link in the source root (e.g. placing a project in `/tmp`) 
 
 ## Limitations
 
 * Swift Package Manager (SPM) dependencies are not supported. _Because SPM does not allow customizing Build Settings, XCRemoteCache cannot specify `clang` and `swiftc` wrappers that control if the local compilation should be skipped (cache hit) or not (cache miss)_
 * Filenames with `_vers.c` suffix are reserved and cannot be used as a source file
 * All compilation files should be referenced via the git repo root. Referencing `/AbsolutePath/someOther.swift` or `../../someOther.swift` that resolve to the location outside of the git repo root is prohibited.
+* Using "Precompiled prefix headers" for Objective-C targets is not yet supported. [PR is welcome]
 
 ## FAQ
 

docs/FAQ.md

@@ -50,3 +50,18 @@ log show --predicate 'sender == "xcprepare"' --style compact --info --debug -las
 log show --predicate 'sender BEGINSWITH "xc"' --style compact --info --debug -last 10m
 ```
 </details>
+
+### Troubleshooting cache misses
+
+Here is a non-exhaustive list of steps that may help with troubleshooting poor cache hit rate.
+
+1. ***Producer&Consumer:*** Review XCRemoteCache [Requirements](../#Requirements) and [Limitations](../#limitations)
+1. ***Producer&Consumer:*** Make sure a producer build uses the same architecture(s) as a consumer. You can inspect `ARCHS` Build Setting in Xcode's Script Phase output logs. Navigate to the report navigator (⌘+9) and expand XCRemoteCache's `prebuild` step output using the "collapsed menu icon" (aka hamburger menu)
+1. ***Producer:*** Verify that all Xcode targets have a Build Phase called `postbuild`
+1. ***Producer:*** If you are using optional XCRemoteCache auto-marking feature (`--final-producer-target` or `final_target`) verify an extra Build Phase called `mark` is added to the specified target
+1. ***Producer:*** After a full build, review logs according to [docs](#how-can-i-find-xcremotecache-logs)
+1. ***Consumer:*** Verify that all Xcode targets have extra XCRemoteCache Build Phase called `prebuild` and `postbuild`
+1. ***Consumer:*** After a full build, review according to [docs](#how-can-i-find-xcremotecache-logs). Find a ***first:*** target that reports a cache miss with a message like `Prebuild step failed with error: ...`. If a target reports faces a cache miss, it may have a knock-on effect where a lot of its consumers (dependant targets) need to be built locally too
+1. ***Consumer:*** ***After a full build, review all meta files placed in `~/Library/Caches/XCRemoteCache/{your_host_path}/meta/*.json` and make sure no absolute paths are used in its `dependencies`. All paths should start a placeholder, like `$(SRCROOT)` or `$(BUILD_DIR)`***
+1. ***Consumer:*** If you are integrating XCRemoteCache and rebuild artifacts for the same sha, previously downloaded artifacts placed in a local cache may still be used on a consumer side. You can either manually delete your local cache at `~/Library/Caches/XCRemoteCache/` before any consumer build or disable a local cache with `artifact_maximum_age: 0` property in `.rcinfo`
+1. ***Consumer:*** To find an actual cache hit, before building in Xcode reset statistics with `xcprepare stats --reset` and once it is done, call `xcprepare stats` to find a cache hit rate