auto merge of #8684 : michaelwoerister/rust/stepping_and_scope_fixes, r=jdm

This PR contains some code cleanup and the fix for issue #8670.
~~I am not sure about issue #8442 (could not reproduce it). @jdm, could check after this is merged and possibly close the issue then?~~ (closed now)

Some interesting facts: With this commit, it should be possible to compile libstd with `-Zdebug-info` (it does not work yet with `-Zextra-debug-info` but we are getting there). Switching debug info on increases the compile time for libstd by about 2 seconds.

@catamorphism I get one failing test in rustpkg:
`package_script_with_default_build` says: `task <unnamed> failed at 'Couldn't copy file', /home/mw/rust/src/librustpkg/tests.rs:689`
Would you have any idea what that is about? Seems be something wrong on my machine...

Cheers,
Michael

Fixes #8670

Author: bors

src/librustc/middle/trans/base.rs

@@ -137,6 +137,13 @@ fn fcx_has_nonzero_span(fcx: &FunctionContext) -> bool {
     }
 }
 
+fn span_is_empty(opt_span: &Option<span>) -> bool {
+    match *opt_span {
+        None => true,
+        Some(span) => *span.lo == 0 && *span.hi == 0
+    }
+}
+
 struct StatRecorder<'self> {
     ccx: @mut CrateContext,
     name: &'self str,
@@ -1624,6 +1631,13 @@ pub fn new_fn_ctxt_w_id(ccx: @mut CrateContext,
         }
     };
     let uses_outptr = type_of::return_uses_outptr(ccx.tcx, substd_output_type);
+
+    let debug_context = if id != -1 && ccx.sess.opts.debuginfo && !span_is_empty(&sp) {
+        Some(debuginfo::create_function_debug_context(ccx, id, param_substs, llfndecl))
+    } else {
+        None
+    };
+
     let fcx = @mut FunctionContext {
           llfn: llfndecl,
           llenv: unsafe {
@@ -1644,7 +1658,7 @@ pub fn new_fn_ctxt_w_id(ccx: @mut CrateContext,
           span: sp,
           path: path,
           ccx: ccx,
-          debug_context: None,
+          debug_context: debug_context,
     };
     fcx.llenv = unsafe {
           llvm::LLVMGetParam(llfndecl, fcx.env_arg_pos() as c_uint)
@@ -1877,6 +1891,7 @@ pub fn trans_closure(ccx: @mut CrateContext,
                                param_substs,
                                body.info(),
                                Some(body.span));
+
     let raw_llargs = create_llargs_for_fn_args(fcx, self_arg, decl.inputs);
 
     // Set the fixed stack segment flag if necessary.
@@ -1885,10 +1900,6 @@ pub fn trans_closure(ccx: @mut CrateContext,
         set_fixed_stack_segment(fcx.llfn);
     }
 
-    if ccx.sess.opts.debuginfo && fcx_has_nonzero_span(fcx) {
-        debuginfo::create_function_metadata(fcx);
-    }
-
     // Create the first basic block in the function and keep a handle on it to
     //  pass to finish_fn later.
     let bcx_top = fcx.entry_bcx.unwrap();
@@ -1900,6 +1911,11 @@ pub fn trans_closure(ccx: @mut CrateContext,
 
     maybe_load_env(fcx);
 
+    // Up until here, IR instructions for this function have explicitly not been annotated with
+    // source code location, so we don't step into call setup code. From here on, source location
+    // emitting should be enabled.
+    debuginfo::start_emitting_source_locations(fcx);
+
     // This call to trans_block is the place where we bridge between
     // translation calls that don't have a return value (trans_crate,
     // trans_mod, trans_item, et cetera) and those that do