[SR-8135] Changes for bug fix to do a clang check only when needed fo…

…r certain … (#1695)

* Changes for bug fix to do a clang check only when needed for certain commands

* Code review changes. Changed lookup and envSearchPaths to be a method and property of UserToolchain class

Sources/Build/Toolchain.swift

@@ -16,7 +16,7 @@ public protocol Toolchain {
     var swiftCompiler: AbsolutePath { get }
 
     /// Path of the `clang` compiler.
-    var clangCompiler: AbsolutePath { get }
+    func getClangCompiler() throws -> AbsolutePath
 
     /// Additional flags to be passed to the C compiler.
     var extraCCFlags: [String] { get }

Sources/Build/llbuild.swift

@@ -100,7 +100,7 @@ public struct LLBuildManifestGenerator {
                     buildByDefault: plan.graph.reachableTargets.contains(target),
                     isTest: description.isTestTarget)
             case .clang(let description):
-                targets.append(createClangCompileTarget(description),
+                targets.append(try createClangCompileTarget(description),
                     buildByDefault: plan.graph.reachableTargets.contains(target),
                     isTest: description.isTestTarget)
             }
@@ -272,14 +272,14 @@ public struct LLBuildManifestGenerator {
     }
 
     /// Create a llbuild target for a Clang target description.
-    private func createClangCompileTarget(_ target: ClangTargetBuildDescription) -> Target {
+    private func createClangCompileTarget(_ target: ClangTargetBuildDescription) throws -> Target {
 
         let standards = [
             (target.clangTarget.cxxLanguageStandard, SupportedLanguageExtension.cppExtensions),
             (target.clangTarget.cLanguageStandard, SupportedLanguageExtension.cExtensions),
         ]
 
-        let commands: [Command] = target.compilePaths().map({ path in
+        let commands: [Command] = try target.compilePaths().map({ path in
             var args = target.basicArguments()
             args += ["-MD", "-MT", "dependencies", "-MF", path.deps.asString]
 
@@ -298,7 +298,7 @@ public struct LLBuildManifestGenerator {
                 //FIXME: Should we add build time dependency on dependent targets?
                 inputs: [path.source.asString],
                 outputs: [path.object.asString],
-                args: [plan.buildParameters.toolchain.clangCompiler.asString] + args,
+                args: [try plan.buildParameters.toolchain.getClangCompiler().asString] + args,
                 deps: path.deps.asString)
             return Command(name: path.object.asString, tool: clang)
         })

Sources/Commands/UserToolchain.swift

@@ -38,9 +38,6 @@ public struct UserToolchain: Toolchain {
     /// Path of the `swiftc` compiler.
     public let swiftCompiler: AbsolutePath
 
-    /// Path of the `clang` compiler.
-    public let clangCompiler: AbsolutePath
-
     public let extraCCFlags: [String]
 
     public let extraSwiftCFlags: [String]
@@ -69,6 +66,9 @@ public struct UserToolchain: Toolchain {
     /// The compilation destination object.
     let destination: Destination
 
+    /// Search paths from the PATH environment variable.
+    let envSearchPaths: [AbsolutePath]
+
     /// Returns the runtime library for the given sanitizer.
     func runtimeLibrary(for sanitizer: Sanitizer) throws -> AbsolutePath {
         // FIXME: This is only for SwiftPM development time support. It is OK
@@ -122,33 +122,16 @@ public struct UserToolchain: Toolchain {
         return (SWIFT_EXEC ?? resolvedBinDirCompiler, SWIFT_EXEC_MANIFEST ?? resolvedBinDirCompiler)
     }
 
-    public init(destination: Destination) throws {
-        self.destination = destination
-
-        // Get the search paths from PATH.
-        let envSearchPaths = getEnvSearchPaths(
-            pathString: getenv("PATH"), currentWorkingDirectory: localFileSystem.currentWorkingDirectory)
-
-        func lookup(fromEnv: String) -> AbsolutePath? {
-            return lookupExecutablePath(
-                filename: getenv(fromEnv),
-                searchPaths: envSearchPaths)
-        }
-
-        // Get the binDir from destination.
-        let binDir = destination.binDir
+    private static func lookup(variable: String, searchPaths: [AbsolutePath]) -> AbsolutePath? {
+        return lookupExecutablePath(filename: getenv(variable), searchPaths: searchPaths)
+    }
 
-        let swiftCompilers = try UserToolchain.determineSwiftCompilers(binDir: binDir, lookup: lookup(fromEnv:))
-        self.swiftCompiler = swiftCompilers.compile
+    public func getClangCompiler() throws -> AbsolutePath {
 
-        // Look for llbuild in bin dir.
-        llbuild = binDir.appending(component: "swift-build-tool")
-        guard localFileSystem.exists(llbuild) else {
-            throw Error.invalidToolchain(problem: "could not find `llbuild` at expected path \(llbuild.asString)")
-        }
+        let clangCompiler: AbsolutePath
 
         // Find the Clang compiler, looking first in the environment.
-        if let value = lookup(fromEnv: "CC") {
+        if let value = UserToolchain.lookup(variable: "CC", searchPaths: envSearchPaths) {
             clangCompiler = value
         } else {
             // No value in env, so search for `clang`.
@@ -163,6 +146,30 @@ public struct UserToolchain: Toolchain {
         guard localFileSystem.isExecutableFile(clangCompiler) else {
             throw Error.invalidToolchain(problem: "could not find `clang` at expected path \(clangCompiler.asString)")
         }
+        return clangCompiler
+    }
+
+    public init(destination: Destination) throws {
+        self.destination = destination
+
+        // Get the search paths from PATH.
+        let searchPaths = getEnvSearchPaths(
+            pathString: getenv("PATH"), currentWorkingDirectory: localFileSystem.currentWorkingDirectory)
+
+        self.envSearchPaths = searchPaths
+
+        // Get the binDir from destination.
+        let binDir = destination.binDir
+
+        let swiftCompilers = try UserToolchain.determineSwiftCompilers(binDir: binDir, lookup: { UserToolchain.lookup(variable: $0, searchPaths: searchPaths) })
+        self.swiftCompiler = swiftCompilers.compile
+
+        // Look for llbuild in bin dir.
+        llbuild = binDir.appending(component: "swift-build-tool")
+        guard localFileSystem.exists(llbuild) else {
+            throw Error.invalidToolchain(problem: "could not find `llbuild` at expected path \(llbuild.asString)")
+        }
+
 
         // We require xctest to exist on macOS.
       #if os(macOS)

Tests/BuildTests/BuildPlanTests.swift

@@ -19,7 +19,6 @@ import PackageModel
 
 private struct MockToolchain: Toolchain {
     let swiftCompiler = AbsolutePath("/fake/path/to/swiftc")
-    let clangCompiler = AbsolutePath("/fake/path/to/clang")
     let extraCCFlags: [String] = []
     let extraSwiftCFlags: [String] = []
     #if os(macOS)
@@ -32,6 +31,9 @@ private struct MockToolchain: Toolchain {
   #else
     let dynamicLibraryExtension = "so"
   #endif
+    func getClangCompiler() throws -> AbsolutePath {
+        return AbsolutePath("/fake/path/to/clang")
+    }
 }
 
 final class BuildPlanTests: XCTestCase {