Consolidate pkgConfig diagnostics (#3767)

It makes more sense to emit all pkgConfig related diagnostics as part of `pkgConfigArgs(for:)` so that clients of libSwiftPM won't have to duplicate them.

Author: neonichu

Sources/Build/BuildPlan.swift

@@ -1996,16 +1996,6 @@ public class BuildPlan {
         let results = pkgConfigArgs(for: target, fileSystem: self.fileSystem, observabilityScope: self.observabilityScope)
         var ret: [(cFlags: [String], libs: [String])] = []
         for result in results {
-            // If there is no pc file on system and we have an available provider, emit a warning.
-            if let provider = result.provider, result.couldNotFindConfigFile {
-                self.observabilityScope.emit(.pkgConfigHint(pkgConfigName: result.pkgConfigName, installText: provider.installText))
-            } else if let error = result.error {
-                self.observabilityScope.emit(
-                    warning: "\(error)",
-                    metadata: .pkgConfig(pcFile: result.pkgConfigName, targetName: target.name)
-                )
-            }
-
             ret.append((result.cFlags, result.libs))
         }
 
@@ -2063,11 +2053,7 @@ private extension Basics.Diagnostic {
             """)
     }
 
-    static func pkgConfigHint(pkgConfigName: String, installText: String) -> Self {
-        .warning("you may be able to install \(pkgConfigName) using your system-packager:\n\(installText)")
-    }
-
-    static func binaryTargetsNotSupported() -> Self {
+    static func binaryTargetsNotSupported() -> Diagnostic.Message {
         .error("binary targets are not supported on this platform")
     }
 }

Sources/PackageLoading/Target+PkgConfig.swift

@@ -67,6 +67,7 @@ public func pkgConfigArgs(for target: SystemLibraryTarget, brewPrefix: AbsoluteP
    var ret: [PkgConfigResult] = []
     // Get the pkg config flags.
     for pkgConfigName in pkgConfigNames.components(separatedBy: " ") {
+        let result: PkgConfigResult
         do {
             let pkgConfig = try PkgConfig(
                 name: pkgConfigName,
@@ -88,16 +89,28 @@ public func pkgConfigArgs(for target: SystemLibraryTarget, brewPrefix: AbsoluteP
                 error = PkgConfigError.prohibitedFlags(filtered.unallowed.joined(separator: ", "))
             }
 
-            ret.append(PkgConfigResult(
+            result = PkgConfigResult(
                     pkgConfigName: pkgConfigName,
                     cFlags: cFlags,
                     libs: libs,
                     error: error,
                     provider: provider
-            ))
+            )
         } catch {
-            ret.append(PkgConfigResult(pkgConfigName: pkgConfigName, error: error, provider: provider))
+            result = PkgConfigResult(pkgConfigName: pkgConfigName, error: error, provider: provider)
         }
+
+        // If there is no pc file on system and we have an available provider, emit a warning.
+        if let provider = result.provider, result.couldNotFindConfigFile {
+            observabilityScope.emit(warning: "you may be able to install \(result.pkgConfigName) using your system-packager:\n\(provider.installText)")
+        } else if let error = result.error {
+            observabilityScope.emit(
+                warning: "\(error)",
+                metadata: .pkgConfig(pcFile: result.pkgConfigName, targetName: target.name)
+            )
+        }
+
+        ret.append(result)
     }
     return ret
 }