[PkgConfig] Do not emit 'pkg-config not installed' diagnostic unless we failed to find a pc file

Author: George

Sources/SPMUtility/PkgConfig.swift

@@ -45,6 +45,7 @@ struct PCFileFinder {
 
  /// Cached results of locations `pkg-config` will search for `.pc` files
  private(set) static var pkgConfigPaths: [AbsolutePath]? // FIXME: @testable(internal)
+ private static var shouldEmitPkgConfigPathsDiagnostic = false
 
  /// The built-in search path list.
  ///
@@ -75,7 +76,7 @@ struct PCFileFinder {
  args: pkgConfigPath, "--variable", "pc_path", "pkg-config").spm_chomp()
  PCFileFinder.pkgConfigPaths = searchPaths.split(separator: ":").map({ AbsolutePath(String($0)) })
  } catch {
- diagnostics.emit(data: PkgConfigExecutionDiagnostic())
+ PCFileFinder.shouldEmitPkgConfigPathsDiagnostic = true
  PCFileFinder.pkgConfigPaths = []
  }
  }
@@ -95,6 +96,10 @@ struct PCFileFinder {
  return pcFile
  }
  }
+ if PCFileFinder.shouldEmitPkgConfigPathsDiagnostic {
+ PCFileFinder.shouldEmitPkgConfigPathsDiagnostic = false
+ diagnostics.emit(data: PkgConfigExecutionDiagnostic())
+ }
  throw PkgConfigError.couldNotFindConfigFile
  }
 }