Make all static library exports contribute to dlls on Windows

changelog/static_libraries_exported_dll.dd

@@ -0,0 +1,8 @@
+Static libraries now contribute towards DLL exports on Windows
+
+Previously if you did not explicitly pull in an object file within a static library, it was elided by the linker automatically.
+This pulls them in automatically for linkers compatible with Microsoft's linker via the ``/WHOLEARCHIVE:file`` flag. Supports LLD.
+
+It does not affect executables, although DLL's being built as dependencies by DUB will include it.
+
+If you have previously used a linker script (.def) or ``/WHOLEARCHIVE`` you may be able to remove them from your builds.

source/dub/compilers/compiler.d

@@ -217,6 +217,9 @@ interface Compiler {
 
 		return build_platform;
 	}
+
+	/// Given a platform specification, determine if a compiler is on Windows and PE-COFF with MSVC link compatible linker.
+	bool isWindowsCOFF(in BuildPlatform platform);
 }
 
 private {

source/dub/compilers/dmd.d

@@ -434,4 +434,10 @@ config    /etc/dmd.conf
 				    || arg.startsWith("-defaultlib=");
 		}
 	}
+
+	bool isWindowsCOFF(in BuildPlatform platform)
+	{
+		// x86_omf and x86_mscoff shouldn't be something you have to worry about here, but just in case something leaks
+		return platform.isWindows && platform.architecture.canFind("x86", "x86_64", "x86_mscoff") && !platform.architecture.canFind("x86_omf");
+	}
 }

source/dub/compilers/gdc.d

@@ -259,6 +259,11 @@ class GDCCompiler : Compiler {
 
 		return  dflags;
 	}
+
+	bool isWindowsCOFF(in BuildPlatform platform)
+	{
+		return false;
+	}
 }
 
 private string extractTarget(const string[] args) { auto i = args.countUntil("-o"); return i >= 0 ? args[i+1] : null; }

source/dub/compilers/ldc.d

@@ -322,4 +322,10 @@ config    /etc/ldc2.conf (x86_64-pc-linux-gnu)
 				    || arg.startsWith("-mtriple=");
 		}
 	}
+
+	bool isWindowsCOFF(in BuildPlatform platform)
+	{
+		// What will happen on ARM Windows? Who knows. Once LDC ships for ARM, lets find out!
+		return platform.isWindows();
+	}
 }

source/dub/generators/build.d

@@ -97,7 +97,32 @@ class BuildGenerator : ProjectGenerator {
 		const copyDynamicLibDepsLinkerFiles = rootTT == TargetType.dynamicLibrary || rootTT == TargetType.none;
 		const copyDynamicLibDepsRuntimeFiles = copyDynamicLibDepsLinkerFiles || rootTT == TargetType.executable;
 
-		bool[string] visited;
+		// Check to see if given a compiler and platform target
+		//  are Windows and linking using a MSVC link compatible linker.
+		const isWindowsCOFF = settings.compiler.isWindowsCOFF(settings.platform);
+
+		bool[string] visited, visitedStaticInDll;
+
+		void visitStaticLibsInDll(ref BuildSettings bs, string target) {
+			if (target in visitedStaticInDll) return;
+			visitedStaticInDll[target] = true;
+
+			auto ti = targets[target];
+			if (ti.buildSettings.targetType != TargetType.staticLibrary)
+				return;
+
+			const ldepPath = target_paths[target].toNativeString();
+
+			// Add the MSVC link /WHOLEARCHIVE flag with static library path passed in
+			//  the purpose of this is to allow all exports from a static library to contribute
+			//  towards the dll's exports.
+			bs.addLFlags("/WHOLEARCHIVE:" ~ ldepPath);
+
+			foreach (ldep; ti.linkDependencies) {
+				visitStaticLibsInDll(bs, ldep);
+			}
+		}
+
 		void buildTargetRec(string target)
 		{
 			if (target in visited) return;
@@ -111,6 +136,17 @@ class BuildGenerator : ProjectGenerator {
 			NativePath[] additional_dep_files;
 			auto bs = ti.buildSettings.dup;
 			const tt = bs.targetType;
+
+			// Windows only behavior for DLL's with static library dependencies
+			if (tt == TargetType.dynamicLibrary && isWindowsCOFF) {
+				// discover all static libraries that are going into our DLL
+				visitedStaticInDll = null;
+
+				foreach (ldep; ti.linkDependencies) {
+					visitStaticLibsInDll(bs, ldep);
+				}
+			}
+
 			foreach (ldep; ti.linkDependencies) {
 				const ldepPath = target_paths[ldep].toNativeString();
 				const doLink = tt != TargetType.staticLibrary && !(bs.options & BuildOption.syntaxOnly);