MSVC: Give hint about possible reason for missing import lib

If an import lib is unexpectedly not present, the reason is usually that
no symbols are exported from the DLL. This is not obvious at all, so
catch this condition and explain what is happening.

Task-number: QBS-1291
Change-Id: Ia2df8e1a27e0231e855413245703ffc05221722e
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

1 files changed, 23 insertions, 4 deletions

diff --git a/share/qbs/modules/cpp/msvc.js b/share/qbs/modules/cpp/msvc.js
index 698f44398..2e2c28c49 100644
--- a/share/qbs/modules/cpp/msvc.js
+++ b/share/qbs/modules/cpp/msvc.js
@@ -262,8 +262,8 @@ function collectLibraryDependencies(product) {
     var seen = {};
     var result = [];
 
-    function addFilePath(filePath, wholeArchive) {
-        result.push({ filePath: filePath, wholeArchive: wholeArchive });
+    function addFilePath(filePath, wholeArchive, productName) {
+        result.push({ filePath: filePath, wholeArchive: wholeArchive, productName: productName });
     }
 
     function addArtifactFilePaths(dep, artifacts) {
@@ -271,8 +271,12 @@ function collectLibraryDependencies(product) {
             return;
         var artifactFilePaths = artifacts.map(function(a) { return a.filePath; });
         var wholeArchive = dep.parameters.cpp && dep.parameters.cpp.linkWholeArchive;
-        for (var i = 0; i < artifactFilePaths.length; ++i)
-            addFilePath(artifactFilePaths[i], wholeArchive);
+        var artifactsAreImportLibs = artifacts.length > 0
+                && artifacts[0].fileTags.contains("dynamiclibrary_import");
+        for (var i = 0; i < artifactFilePaths.length; ++i) {
+            addFilePath(artifactFilePaths[i], wholeArchive,
+                        artifactsAreImportLibs ? dep.name : undefined);
+        }
     }
 
     function addExternalLibs(obj) {
@@ -467,6 +471,21 @@ function prepareLinker(project, product, inputs, outputs, input, output) {
         args = wrapperArgs.concat(args);
     }
     var commands = [];
+    var warningCmd = new JavaScriptCommand();
+    warningCmd.silent = true;
+    warningCmd.libDeps = libDeps;
+    warningCmd.sourceCode = function() {
+        for (var i = 0; i < libDeps.length; ++i) {
+            if (!libDeps[i].productName || File.exists(libDeps[i].filePath))
+                continue;
+            console.warn("Import library '" + FileInfo.toNativeSeparators(libDeps[i].filePath)
+                         + "' does not exist. This typically happens when a DLL does not "
+                         + "export any symbols. Please make sure the '" + libDeps[i].productName
+                         + "' library exports symbols, or, if you do not intend to actually "
+                         + "link against it, specify \"cpp.link: false\" in the Depends item.");
+        }
+    };
+    commands.push(warningCmd);
     var cmd = new Command(linkerPath, args)
     cmd.description = 'linking ' + primaryOutput.fileName;
     cmd.highlight = 'linker';