From 3c90baaf6c87aa401323a7813aa32735ba811706 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Mon, 18 Jun 2018 21:49:23 -0700
Subject: [PATCH 1/2] Prefer object sourcemaps over file-inlined sourcemaps.

---
 .../src/transformation/normalize-file.js      | 24 +++++++++++--------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/packages/babel-core/src/transformation/normalize-file.js b/packages/babel-core/src/transformation/normalize-file.js
index fa4d03505d..22ea4ef470 100644
--- a/packages/babel-core/src/transformation/normalize-file.js
+++ b/packages/babel-core/src/transformation/normalize-file.js
@@ -27,15 +27,23 @@ export default function normalizeFile(
 
   let inputMap = null;
   if (options.inputSourceMap !== false) {
-    try {
-      inputMap = convertSourceMap.fromSource(code);
+    // If an explicit object is passed in, it overrides the processing of
+    // source maps that may be in the file itself.
+    if (typeof options.inputSourceMap === "object") {
+      inputMap = convertSourceMap.fromObject(options.inputSourceMap);
+    }
 
-      if (inputMap) {
+    if (!inputMap) {
+      try {
+        inputMap = convertSourceMap.fromSource(code);
+
+        if (inputMap) {
+          code = convertSourceMap.removeComments(code);
+        }
+      } catch (err) {
+        debug("discarding unknown inline input sourcemap", err);
         code = convertSourceMap.removeComments(code);
       }
-    } catch (err) {
-      debug("discarding unknown inline input sourcemap", err);
-      code = convertSourceMap.removeComments(code);
     }
 
     if (!inputMap) {
@@ -50,10 +58,6 @@ export default function normalizeFile(
         code = convertSourceMap.removeMapFileComments(code);
       }
     }
-
-    if (!inputMap && typeof options.inputSourceMap === "object") {
-      inputMap = convertSourceMap.fromObject(options.inputSourceMap);
-    }
   }
 
   if (ast) {

From 532c25c8db5b2f95271f5cd0d70e762f891cfde4 Mon Sep 17 00:00:00 2001
From: Logan Smyth <loganfsmyth@gmail.com>
Date: Mon, 18 Jun 2018 22:06:08 -0700
Subject: [PATCH 2/2] Ensure that file-path sourcemaps load relative to the
 file containing the comment.

---
 lib/third-party-libs.js.flow                  |  2 +-
 .../src/transformation/normalize-file.js      | 19 ++++++++++++++-----
 2 files changed, 15 insertions(+), 6 deletions(-)

diff --git a/lib/third-party-libs.js.flow b/lib/third-party-libs.js.flow
index 1b6ef25940..cd048815a4 100644
--- a/lib/third-party-libs.js.flow
+++ b/lib/third-party-libs.js.flow
@@ -160,7 +160,7 @@ declare module "convert-source-map" {
     fromComment(str: string): Converter,
     fromMapFileComment(str: string): Converter,
     fromSource(str: string): Converter,
-    fromMapFileSource(str: string): Converter,
+    fromMapFileSource(str: string, dir: string): Converter,
     removeComments(str: string): string,
     removeMapFileComments(str: string): string,
     generateMapFileComment(path: string, options?: ?{ multiline: boolean }): string,
diff --git a/packages/babel-core/src/transformation/normalize-file.js b/packages/babel-core/src/transformation/normalize-file.js
index 22ea4ef470..203488acd6 100644
--- a/packages/babel-core/src/transformation/normalize-file.js
+++ b/packages/babel-core/src/transformation/normalize-file.js
@@ -1,5 +1,6 @@
 // @flow
 
+import path from "path";
 import buildDebug from "debug";
 import * as t from "@babel/types";
 import type { PluginPasses } from "../config";
@@ -47,14 +48,22 @@ export default function normalizeFile(
     }
 
     if (!inputMap) {
-      try {
-        inputMap = convertSourceMap.fromMapFileSource(code);
+      if (typeof options.filename === "string") {
+        try {
+          inputMap = convertSourceMap.fromMapFileSource(
+            code,
+            path.dirname(options.filename),
+          );
 
-        if (inputMap) {
+          if (inputMap) {
+            code = convertSourceMap.removeMapFileComments(code);
+          }
+        } catch (err) {
+          debug("discarding unknown file input sourcemap", err);
           code = convertSourceMap.removeMapFileComments(code);
         }
-      } catch (err) {
-        debug("discarding unknown file input sourcemap", err);
+      } else {
+        debug("discarding un-loadable file input sourcemap");
         code = convertSourceMap.removeMapFileComments(code);
       }
     }