auto merge of #8329 : michaelwoerister/rust/lexical_scopes_alt, r=graydon

This pull request re-implements handling of visibility scopes and source code positions in debug info. It should now be very stable and properly handle

+ variable shadowing
+ expanded code (macros and the new for-loop de-sugaring, for example)
+ variables in the middle of nested scopes
+ bindings declared in the head of match statement arms. 

all of which did not work at all or did not work reliably before. Those interested in a more detailed description of the problems at hand, I kindly refer to http://michaelwoerister.github.io/2013/08/03/visibility-scopes.html

Why doesn't the `populate_scope_map()` function use `syntax::visit`?
Because it would not improve this particular AST walker (see: michaelwoerister@69dc790#commitcomment-3781426)

Cheers,
Michael

Author: bors

src/librustc/middle/trans/_match.rs

@@ -214,6 +214,7 @@ use middle::trans::expr;
 use middle::trans::glue;
 use middle::trans::tvec;
 use middle::trans::type_of;
+use middle::trans::debuginfo;
 use middle::ty;
 use util::common::indenter;
 use util::ppaux::{Repr, vec_map_to_str};
@@ -385,6 +386,7 @@ struct BindingInfo {
     llmatch: ValueRef,
     trmode: TransBindingMode,
     id: ast::NodeId,
+    span: span,
     ty: ty::t,
 }
 
@@ -1305,7 +1307,7 @@ fn insert_lllocals(bcx: @mut Block,
         BindArgument => bcx.fcx.llargs
     };
 
-    for (_, &binding_info) in bindings_map.iter() {
+    for (&ident, &binding_info) in bindings_map.iter() {
         let llval = match binding_info.trmode {
             // By value bindings: use the stack slot that we
             // copied/moved the value into
@@ -1325,6 +1327,14 @@ fn insert_lllocals(bcx: @mut Block,
 
         debug!("binding %? to %s", binding_info.id, bcx.val_to_str(llval));
         llmap.insert(binding_info.id, llval);
+
+        if bcx.sess().opts.extra_debuginfo {
+            debuginfo::create_match_binding_metadata(bcx,
+                                                     ident,
+                                                     binding_info.id,
+                                                     binding_info.ty,
+                                                     binding_info.span);
+        }
     }
     return bcx;
 }
@@ -1771,7 +1781,7 @@ fn create_bindings_map(bcx: @mut Block, pat: @ast::pat) -> BindingsMap {
     let ccx = bcx.ccx();
     let tcx = bcx.tcx();
     let mut bindings_map = HashMap::new();
-    do pat_bindings(tcx.def_map, pat) |bm, p_id, _s, path| {
+    do pat_bindings(tcx.def_map, pat) |bm, p_id, span, path| {
         let ident = path_to_ident(path);
         let variable_ty = node_id_type(bcx, p_id);
         let llvariable_ty = type_of::type_of(ccx, variable_ty);
@@ -1793,8 +1803,11 @@ fn create_bindings_map(bcx: @mut Block, pat: @ast::pat) -> BindingsMap {
             }
         };
         bindings_map.insert(ident, BindingInfo {
-            llmatch: llmatch, trmode: trmode,
-            id: p_id, ty: variable_ty
+            llmatch: llmatch,
+            trmode: trmode,
+            id: p_id,
+            span: span,
+            ty: variable_ty
         });
     }
     return bindings_map;

src/librustc/middle/trans/base.rs

@@ -1103,7 +1103,6 @@ pub fn trans_stmt(cx: @mut Block, s: &ast::stmt) -> @mut Block {
     }
 
     let mut bcx = cx;
-    debuginfo::update_source_pos(cx, s.span);
 
     match s.node {
         ast::stmt_expr(e, _) | ast::stmt_semi(e, _) => {
@@ -1634,7 +1633,8 @@ pub fn new_fn_ctxt_w_id(ccx: @mut CrateContext,
           param_substs: param_substs,
           span: sp,
           path: path,
-          ccx: ccx
+          ccx: ccx,
+          debug_context: None,
     };
     fcx.llenv = unsafe {
           llvm::LLVMGetParam(llfndecl, fcx.env_arg_pos() as c_uint)
@@ -1933,7 +1933,7 @@ pub fn trans_fn(ccx: @mut CrateContext,
                   attrs,
                   output_type,
                   |fcx| {
-                      if ccx.sess.opts.extra_debuginfo
+                      if ccx.sess.opts.debuginfo
                           && fcx_has_nonzero_span(fcx) {
                           debuginfo::create_function_metadata(fcx);
                       }

src/librustc/middle/trans/common.rs

@@ -23,6 +23,7 @@ use middle::trans::build;
 use middle::trans::datum;
 use middle::trans::glue;
 use middle::trans::write_guard;
+use middle::trans::debuginfo;
 use middle::ty::substs;
 use middle::ty;
 use middle::typeck;
@@ -226,7 +227,10 @@ pub struct FunctionContext {
     path: path,
 
     // This function's enclosing crate context.
-    ccx: @mut CrateContext
+    ccx: @mut CrateContext,
+
+    // Used and maintained by the debuginfo module.
+    debug_context: Option<~debuginfo::FunctionDebugContext>
 }
 
 impl FunctionContext {

src/librustc/middle/trans/controlflow.rs

@@ -19,7 +19,6 @@ use middle::trans::base::*;
 use middle::trans::build::*;
 use middle::trans::callee;
 use middle::trans::common::*;
-use middle::trans::debuginfo;
 use middle::trans::expr;
 use middle::trans::type_of::*;
 use middle::ty;
@@ -38,12 +37,10 @@ pub fn trans_block(bcx: @mut Block, b: &ast::Block, dest: expr::Dest) -> @mut Bl
     let _icx = push_ctxt("trans_block");
     let mut bcx = bcx;
     for s in b.stmts.iter() {
-        debuginfo::update_source_pos(bcx, b.span);
         bcx = trans_stmt(bcx, *s);
     }
     match b.expr {
         Some(e) => {
-            debuginfo::update_source_pos(bcx, e.span);
             bcx = expr::trans_into(bcx, e, dest);
         }
         None => {