rustc: Handle linker diagnostic from LLVM

Previously linker diagnostic were being hidden when two modules were linked
together but failed to link. This commit fixes the situation by ensuring that we
have a diagnostic handler installed and also adds support for handling linker
diagnostics.

4 files changed, 22 insertions, 8 deletions

diff --git a/src/librustc_codegen_llvm/back/lto.rs b/src/librustc_codegen_llvm/back/lto.rs
index daa2fb05280..b644422e795 100644
--- a/src/librustc_codegen_llvm/back/lto.rs
+++ b/src/librustc_codegen_llvm/back/lto.rs
@@ -11,7 +11,7 @@
 use back::bytecode::{DecodedBytecode, RLIB_BYTECODE_EXTENSION};
 use back::symbol_export;
 use back::write::{ModuleConfig, with_llvm_pmb, CodegenContext};
-use back::write;
+use back::write::{self, DiagnosticHandlers};
 use errors::{FatalError, Handler};
 use llvm::archive_ro::ArchiveRO;
 use llvm::{True, False};
@@ -234,9 +234,17 @@ fn fat_lto(cgcx: &CodegenContext,
     let module = modules.remove(costliest_module);
     let mut serialized_bitcode = Vec::new();
     {
-        let llmod = module.llvm().expect("can't lto pre-codegened modules").llmod();
+        let (llcx, llmod) = {
+            let llvm = module.llvm().expect("can't lto pre-codegened modules");
+            (&llvm.llcx, llvm.llmod())
+        };
         info!("using {:?} as a base module", module.llmod_id);
 
+        // The linking steps below may produce errors and diagnostics within LLVM
+        // which we'd like to handle and print, so set up our diagnostic handlers
+        // (which get unregistered when they go out of scope below).
+        let _handler = DiagnosticHandlers::new(cgcx, diag_handler, llcx);
+
         // For all other modules we codegened we'll need to link them into our own
         // bitcode. All modules were codegened in their own LLVM context, however,
         // and we want to move everything to the same LLVM context. Currently the
diff --git a/src/librustc_codegen_llvm/back/write.rs b/src/librustc_codegen_llvm/back/write.rs
index db044878fe7..209c3a23c5c 100644
--- a/src/librustc_codegen_llvm/back/write.rs
+++ b/src/librustc_codegen_llvm/back/write.rs
@@ -397,15 +397,15 @@ impl CodegenContext {
     }
 }
 
-struct DiagnosticHandlers<'a> {
+pub struct DiagnosticHandlers<'a> {
     data: *mut (&'a CodegenContext, &'a Handler),
     llcx: &'a llvm::Context,
 }
 
 impl<'a> DiagnosticHandlers<'a> {
-    fn new(cgcx: &'a CodegenContext,
-           handler: &'a Handler,
-           llcx: &'a llvm::Context) -> Self {
+    pub fn new(cgcx: &'a CodegenContext,
+               handler: &'a Handler,
+               llcx: &'a llvm::Context) -> Self {
         let data = Box::into_raw(Box::new((cgcx, handler)));
         unsafe {
             llvm::LLVMRustSetInlineAsmDiagnosticHandler(llcx, inline_asm_handler, data as *mut _);
@@ -475,10 +475,11 @@ unsafe extern "C" fn diagnostic_handler(info: &DiagnosticInfo, user: *mut c_void
                                                 opt.message));
             }
         }
-        llvm::diagnostic::PGO(diagnostic_ref) => {
+        llvm::diagnostic::PGO(diagnostic_ref) |
+        llvm::diagnostic::Linker(diagnostic_ref) => {
             let msg = llvm::build_string(|s| {
                 llvm::LLVMRustWriteDiagnosticInfoToString(diagnostic_ref, s)
-            }).expect("non-UTF8 PGO diagnostic");
+            }).expect("non-UTF8 diagnostic");
             diag_handler.warn(&msg);
         }
         llvm::diagnostic::UnknownDiagnostic(..) => {},
diff --git a/src/librustc_codegen_llvm/llvm/diagnostic.rs b/src/librustc_codegen_llvm/llvm/diagnostic.rs
index 7f2a9d6984a..c41a5f74ae3 100644
--- a/src/librustc_codegen_llvm/llvm/diagnostic.rs
+++ b/src/librustc_codegen_llvm/llvm/diagnostic.rs
@@ -126,6 +126,7 @@ pub enum Diagnostic<'ll> {
     Optimization(OptimizationDiagnostic<'ll>),
     InlineAsm(InlineAsmDiagnostic<'ll>),
     PGO(&'ll DiagnosticInfo),
+    Linker(&'ll DiagnosticInfo),
 
     /// LLVM has other types that we do not wrap here.
     UnknownDiagnostic(&'ll DiagnosticInfo),
@@ -168,6 +169,9 @@ impl Diagnostic<'ll> {
             Dk::PGOProfile => {
                 PGO(di)
             }
+            Dk::Linker => {
+                Linker(di)
+            }
 
             _ => UnknownDiagnostic(di),
         }
diff --git a/src/librustc_codegen_llvm/llvm/ffi.rs b/src/librustc_codegen_llvm/llvm/ffi.rs
index 898d3d67353..989498ea92b 100644
--- a/src/librustc_codegen_llvm/llvm/ffi.rs
+++ b/src/librustc_codegen_llvm/llvm/ffi.rs
@@ -332,6 +332,7 @@ pub enum DiagnosticKind {
     OptimizationRemarkOther,
     OptimizationFailure,
     PGOProfile,
+    Linker,
 }
 
 /// LLVMRustArchiveKind