Run build commands without declared outputs

It is possible to declare build commands without outputs and the expectation is that those would still run. Currently, that is not the case, since the only condition that makes llbuild run build commands is that there's a client for the output files (either compilation or copying of resources).

This change adds a phony output to any command that has no declared outputs and declares these phony outputs as input for any targets that are asking for the plugin to be applied. This will lead to these commands running unconditionally, fixing the current silent failure to run these.

rdar://100415491

Author: neonichu

Sources/Build/BuildManifest/LLBuildManifestBuilder+Clang.swift

@@ -89,7 +89,7 @@ extension LLBuildManifestBuilder {
             )
         }
 
-        try addBuildToolPlugins(.clang(target))
+        let additionalInputs = try addBuildToolPlugins(.clang(target))
 
         // Create a phony node to represent the entire target.
         let targetName = target.target.getLLBuildTargetName(config: target.buildParameters.buildConfig)
@@ -98,7 +98,7 @@ extension LLBuildManifestBuilder {
         self.manifest.addNode(output, toTarget: targetName)
         self.manifest.addPhonyCmd(
             name: output.name,
-            inputs: objectFileNodes,
+            inputs: objectFileNodes + additionalInputs,
             outputs: [output]
         )
 

Sources/Build/BuildManifest/LLBuildManifestBuilder+Swift.swift

@@ -484,14 +484,14 @@ extension LLBuildManifestBuilder {
             }
         }
 
-        try self.addBuildToolPlugins(.swift(target))
+        let additionalInputs = try self.addBuildToolPlugins(.swift(target))
 
         // Depend on any required macro product's output.
         try target.requiredMacroProducts.forEach { macro in
             try inputs.append(.virtual(macro.getLLBuildTargetName(config: target.buildParameters.buildConfig)))
         }
 
-        return inputs
+        return inputs + additionalInputs
     }
 
     /// Adds a top-level phony command that builds the entire target.

Sources/Build/BuildManifest/LLBuildManifestBuilder.swift

@@ -194,7 +194,12 @@ extension LLBuildManifestBuilder {
 // MARK: - Compilation
 
 extension LLBuildManifestBuilder {
-    func addBuildToolPlugins(_ target: TargetBuildDescription) throws {
+    func addBuildToolPlugins(_ target: TargetBuildDescription) throws -> [Node] {
+        // For any build command that doesn't declare any outputs, we need to create a phony output to ensure they will still be run by the build system.
+        var phonyOutputs = [Node]()
+        // If we have multiple commands with no output files and no display name, this serves as a way to disambiguate the virtual nodes being created.
+        var pluginNumber = 1
+
         // Add any regular build commands created by plugins for the target.
         for result in target.buildToolPluginInvocationResults {
             // Only go through the regular build commands — prebuild commands are handled separately.
@@ -213,17 +218,27 @@ extension LLBuildManifestBuilder {
                         writableDirectories: [result.pluginOutputDirectory]
                     )
                 }
+                let additionalOutputs: [Node]
+                if command.outputFiles.isEmpty {
+                    additionalOutputs = [.virtual("\(target.target.c99name)-\(command.configuration.displayName ?? "\(pluginNumber)")")]
+                    phonyOutputs += additionalOutputs
+                    pluginNumber += 1
+                } else {
+                    additionalOutputs = []
+                }
                 self.manifest.addShellCmd(
                     name: displayName + "-" + ByteString(encodingAsUTF8: uniquedName).sha256Checksum,
                     description: displayName,
                     inputs: command.inputFiles.map { .file($0) },
-                    outputs: command.outputFiles.map { .file($0) },
+                    outputs: command.outputFiles.map { .file($0) } + additionalOutputs,
                     arguments: commandLine,
                     environment: command.configuration.environment,
                     workingDirectory: command.configuration.workingDirectory?.pathString
                 )
             }
         }
+
+        return phonyOutputs
     }
 }