UI option to turn on backtrace (RUST_BACKTRACE=1) --- off by default; (and also embed it in shared urls)

static/web.html

@@ -73,6 +73,12 @@
                         <option>att</option>
                         <option>intel</option>
                     </select>
+                    <p><label for=backtrace title="Whether to set the shell environment var RUST_BACKTRACE and thus show the backtrace in the output! eg. to quickly test this run: fn main() { panic!() }">Backtrace:</label>
+                    <select name=backtrace id=backtrace>
+                        <option title="RUST_BACKTRACE is not set" value="0">off</option>
+                        <option title="export RUST_BACKTRACE=1" value="1">on</option>
+                        <option title="'auto' means turn this on only when Mode: Debug but not when Mode: Release" value="2">auto</option>
+                    </select>
                 </div
             ></div>
         </form>

static/web.js

@@ -133,8 +133,8 @@
         result.parentNode.style.visibility = "";
     }
 
-    function evaluate(result, code, version, optimize, button, test) {
-        send("evaluate.json", {code: code, version: version, optimize: optimize, test: !!test, separate_output: true, color: true},
+    function evaluate(result, code, version, optimize, button, test, backtrace) {
+        send("evaluate.json", {code: code, version: version, optimize: optimize, test: !!test, separate_output: true, color: true, backtrace: backtrace },
             function(object) {
                 var samp, pre;
                 set_result(result);
@@ -174,10 +174,10 @@
         }, button, test ? "Running tests…" : "Running…", result);
     }
 
-    function compile(emit, result, code, version, optimize, button) {
+    function compile(emit, result, code, version, optimize, button, backtrace) {
         var syntax = document.getElementById('asm-flavor').value;
         send("compile.json", {emit: emit, code: code, version: version, optimize: optimize,
-                              color: true, highlight: true, syntax: syntax}, function(object) {
+                              color: true, highlight: true, syntax: syntax, backtrace: backtrace}, function(object) {
             if ("error" in object) {
                 set_result(result, "<pre class=\"rustc-output rustc-errors\"><samp></samp></pre>");
                 result.firstChild.firstChild.innerHTML = formatCompilerOutput(object.error);
@@ -233,10 +233,11 @@
         result.parentNode.style.visibility = "";
     }
 
-    function shareGist(result, version, code, button) {
+    function shareGist(result, version, code, button, backtraceval) {
         // only needed for the "shrinking" animation
         var full_url = "https://play.rust-lang.org/?code=" + encodeURIComponent(code) +
-                       "&version=" + encodeURIComponent(version);
+                       "&version=" + encodeURIComponent(version) +
+                       "&backtrace=" + encodeURIComponent(backtraceval);
         var url = "https://api.github.com/gists";
         button.disabled = true;
 
@@ -275,7 +276,8 @@
 
                         var play_url = "https://play.rust-lang.org/?gist=" +
                                        encodeURIComponent(gist_id) + "&version=" +
-                                       encodeURIComponent(version);
+                                       encodeURIComponent(version) +
+                       "&backtrace=" + encodeURIComponent(backtraceval);
 
 
                         var link = result.firstChild.firstElementChild;
@@ -301,9 +303,10 @@
         );
     }
 
-    function share(result, version, code, button) {
+    function share(result, version, code, button, backtraceval) {
         var playurl = "https://play.rust-lang.org/?code=" + encodeURIComponent(code);
         playurl += "&version=" + encodeURIComponent(version);
+        playurl += "&backtrace=" + encodeURIComponent(backtraceval);
         if (playurl.length > 5000) {
             set_result(result, "<p class=error>Sorry, your code is too long to share this way." +
                 "<p class=error-explanation>At present, sharing produces a link containing the" +
@@ -482,6 +485,7 @@
     var mode;
     var query;
     var asm_flavor;
+    var backtrace;
 
     function updateEvaluateAction(code) {
         // A very simple pair of heuristics; there’s no point in doing more, IMO.
@@ -503,7 +507,8 @@
         }
         evaluate(result, session.getValue(), getRadioValue("version"),
                  getRadioValue("optimize"), evaluateButton,
-                 evaluateAction === "test");
+                 evaluateAction === "test",
+                 backtrace.value);
     }
 
     var COLOR_CODES = ['black', 'red', 'green', 'yellow', 'blue', 'magenta', 'cyan', 'white'];
@@ -552,6 +557,7 @@
         clearResultButton = document.getElementById("clear-result");
         keyboard = document.getElementById("keyboard");
         asm_flavor = document.getElementById("asm-flavor");
+        backtrace = document.getElementById("backtrace");
         themes = document.getElementById("themes");
         editor = ace.edit("editor");
         set_result.editor = editor;
@@ -589,6 +595,11 @@
             asm_flavor.value = flavor;
         }
 
+        var vbacktrace = optionalLocalStorageGetItem("backtrace");
+        if (vbacktrace !== null) {
+            backtrace.value = vbacktrace;
+        }
+
         query = getQueryParameters();
         if ("code" in query) {
             session.setValue(query.code);
@@ -610,6 +621,12 @@
             }
         }
 
+        if ("backtrace" in query) {
+            if (backtrace !== null) {
+                backtrace.value = query.backtrace;
+            }
+        }
+
         if (query.run === "1") {
             doEvaluate();
         } else {
@@ -637,6 +654,11 @@
             optionalLocalStorageSetItem("asm_flavor", flavor);
         };
 
+        backtrace.onkeyup = backtrace.onchange = function() {
+            var vbacktrace = backtrace.options[backtrace.selectedIndex].value;
+            optionalLocalStorageSetItem("backtrace", vbacktrace);
+        };
+
         evaluateButton.onclick = function() {
             doEvaluate(true);
         };
@@ -656,30 +678,30 @@
 
         asmButton.onclick = function() {
             compile("asm", result, session.getValue(), getRadioValue("version"),
-                     getRadioValue("optimize"), asmButton);
+                     getRadioValue("optimize"), asmButton, backtrace.value);
         };
 
         irButton.onclick = function() {
             compile("llvm-ir", result, session.getValue(), getRadioValue("version"),
-                     getRadioValue("optimize"), irButton);
+                     getRadioValue("optimize"), irButton, backtrace.value);
         };
 
         mirButton.onclick = function() {
             document.getElementById("version-nightly").checked = true;
             compile("mir", result, session.getValue(), getRadioValue("version"),
-                     getRadioValue("optimize"), mirButton);
+                     getRadioValue("optimize"), mirButton, backtrace.value);
         };
 
         formatButton.onclick = function() {
             format(result, session, getRadioValue("version"), formatButton);
         };
 
         shareButton.onclick = function() {
-            share(result, getRadioValue("version"), session.getValue(), shareButton);
+            share(result, getRadioValue("version"), session.getValue(), shareButton, backtrace.value);
         };
 
         gistButton.onclick = function() {
-            shareGist(result, getRadioValue("version"), session.getValue(), gistButton);
+            shareGist(result, getRadioValue("version"), session.getValue(), gistButton, backtrace.value);
         };
 
         configureEditorButton.onclick = function() {

web.py

@@ -3,6 +3,7 @@
 import functools
 import os
 import sys
+import shlex #for shlex.quote() needed only when backtrace is on, to escape args
 
 from bottle import get, request, response, route, run, static_file
 from pygments import highlight
@@ -32,7 +33,13 @@ def serve_static(path):
     return static_file(path, root="static")
 
 @functools.lru_cache(maxsize=256)
-def execute(version, command, arguments, code):
+def execute(version, command, arguments, code, show_backtrace):
+    if show_backtrace:
+        escapedargs=""
+        for arg in arguments:
+            escapedargs += " " + shlex.quote(arg)
+        arguments = ("-c", "export RUST_BACKTRACE=1; " + command + escapedargs) 
+        command = "/usr/bin/dash"
     print("running:", version, command, arguments, file=sys.stderr, flush=True)
     return playpen.execute(version, command, arguments, code)
 
@@ -57,22 +64,31 @@ def wrapper(*args, **kwargs):
         return wrapper
     return decorator
 
+def init_args_get_bt(optimize, color, backtrace_str):
+    args = ["-C", "opt-level=" + optimize]
+    if "1" == backtrace_str or ( "2" == backtrace_str and "0" == optimize ):
+        show_backtrace = True
+    else:
+        show_backtrace = False
+    if "0" == optimize:
+        args.append("-g")
+    if color:
+        args.append("--color=always")
+    return (args, show_backtrace)
+
 @route("/evaluate.json", method=["POST", "OPTIONS"])
 @enable_post_cors
+@extractor("backtrace", "0", ("0", "1", "2"))
 @extractor("color", False, (True, False))
 @extractor("test", False, (True, False))
 @extractor("version", "stable", ("stable", "beta", "nightly"))
 @extractor("optimize", "2", ("0", "1", "2", "3"))
-def evaluate(optimize, version, test, color):
-    args = ["-C", "opt-level=" + optimize]
-    if optimize == "0":
-        args.append("-g")
-    if color:
-        args.append("--color=always")
+def evaluate(optimize, version, test, color, backtrace_str):
+    args, show_backtrace = init_args_get_bt(optimize, color, backtrace_str)
     if test:
         args.append("--test")
 
-    out, _ = execute(version, "/usr/local/bin/evaluate.sh", tuple(args), request.json["code"])
+    out, _ = execute(version, "/usr/local/bin/evaluate.sh", tuple(args), request.json["code"], show_backtrace)
 
     if request.json.get("separate_output") is True:
         split = out.split(b"\xff", 1)
@@ -87,27 +103,27 @@ def evaluate(optimize, version, test, color):
 
 @route("/format.json", method=["POST", "OPTIONS"])
 @enable_post_cors
+@extractor("optimize", "2", ("0", "1", "2", "3"))
+@extractor("backtrace", "0", ("0", "1", "2"))
 @extractor("version", "stable", ("stable", "beta", "nightly"))
-def format(version):
-    out, rc = execute(version, "/usr/bin/rustfmt", (), request.json["code"])
+def format(version, backtrace_str, optimize):
+    _, show_backtrace = init_args_get_bt(optimize, None, backtrace_str)
+    out, rc = execute(version, "/usr/bin/rustfmt", (), request.json["code"], show_backtrace)
     if rc:
         return {"error": out.decode()}
     else:
         return {"result": out.decode()}
 
 @route("/compile.json", method=["POST", "OPTIONS"])
 @enable_post_cors
+@extractor("backtrace", "0", ("0", "1", "2"))
 @extractor("syntax", "att", ("att", "intel"))
 @extractor("color", False, (True, False))
 @extractor("version", "stable", ("stable", "beta", "nightly"))
 @extractor("optimize", "2", ("0", "1", "2", "3"))
 @extractor("emit", "asm", ("asm", "llvm-ir", "mir"))
-def compile(emit, optimize, version, color, syntax):
-    args = ["-C", "opt-level=" + optimize]
-    if optimize == "0":
-        args.append("-g")
-    if color:
-        args.append("--color=always")
+def compile(emit, optimize, version, color, syntax, backtrace_str):
+    args, show_backtrace = init_args_get_bt(optimize, color, backtrace_str)
     if syntax:
         args.append("-C")
         args.append("llvm-args=-x86-asm-syntax=%s" % syntax)
@@ -116,7 +132,7 @@ def compile(emit, optimize, version, color, syntax):
         args.append("--unpretty=mir")
     else:
         args.append("--emit=" + emit)
-    out, _ = execute(version, "/usr/local/bin/compile.sh", tuple(args), request.json["code"])
+    out, _ = execute(version, "/usr/local/bin/compile.sh", tuple(args), request.json["code"], show_backtrace)
     split = out.split(b"\xff", 1)
     if len(split) == 2:
         rustc_output = split[0].decode()