Make column match fuzzy

Summary:
We are currently very strict about breakpoint location matching. This
diff allows some fuzz in the column, but not in the line.

Changelog: [Internal] Setting Hermes breakpoints no longer requires exact column match

Reviewed By: avp

Differential Revision: D21343198

fbshipit-source-id: a59786a9d63f9fe1ed576835ed660ba3343affe1

lib/BCGen/HBC/DebugInfo.cpp

@@ -169,22 +169,41 @@ OptValue<DebugSearchResult> DebugInfo::getAddressForLocation(
 
   unsigned offset = start;
 
+  // We consider the best match for a location to be the first of:
+  // 1. Exact match
+  // 2. Exact line, largest column before the target
+  // 3. Exact line, any column
+  // If multiple, the lowest bytecode address wins in each category.
+  DebugSearchResult best(0, DebugOffsets::NO_OFFSET, 0, 0);
+
   while (offset < end) {
     FunctionDebugInfoDeserializer fdid(data_.getData(), offset);
     while (auto loc = fdid.next()) {
       uint32_t line = loc->line;
       uint32_t column = loc->column;
-      if (line == targetLine &&
-          (!targetColumn.hasValue() || column == *targetColumn)) {
-        // Short-circuit on a precise match.
-        return DebugSearchResult(
-            fdid.getFunctionIndex(), loc->address, line, column);
+      if (line == targetLine) {
+        if (!targetColumn.hasValue() || column == *targetColumn) {
+          // Short-circuit on a precise match.
+          return DebugSearchResult(
+              fdid.getFunctionIndex(), loc->address, line, column);
+        }
+
+        if (best.bytecodeOffset == DebugOffsets::NO_OFFSET ||
+            (column <= *targetColumn &&
+             (best.column > *targetColumn || column > best.column))) {
+          best = DebugSearchResult(
+              fdid.getFunctionIndex(), loc->address, line, column);
+        }
       }
     }
     offset = fdid.getOffset();
   }
 
-  return llvm::None;
+  if (best.bytecodeOffset == DebugOffsets::NO_OFFSET) {
+    return llvm::None;
+  }
+
+  return best;
 }
 
 /// Read \p count variable names from \p offset into the variable name section

test/debugger/fuzzy-break.js

@@ -0,0 +1,45 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// RUN: %hdb --break-at-start %s < %s.debug | %FileCheck --match-full-lines %s
+// REQUIRES: debugger
+
+function foo() {
+  print('first');
+  print('second'); print('third'); print("fourth");
+  print('fifth'); print('sixth');
+}
+
+function bar() {
+  foo();
+}
+
+bar();
+// CHECK-LABEL: Break on script load {{.+}}
+
+// column=1 is before all statements. Match the first.
+// CHECK-NEXT: Set breakpoint 1 at {{.+}}:12:3
+
+// column=22 is the middle of the 'third' print. Match that.
+// CHECK-NEXT: Set breakpoint 2 at {{.+}}:13:20
+
+// column=200 is after all statements. Match the last.
+// CHECK-NEXT: Set breakpoint 3 at {{.+}}:14:24
+
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: Break on breakpoint 1 in foo: {{.+}}:12:3
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: first
+// CHECK-NEXT: second
+// CHECK-NEXT: Break on breakpoint 2 in foo: {{.+}}:13:20
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: third
+// CHECK-NEXT: fourth
+// CHECK-NEXT: fifth
+// CHECK-NEXT: Break on breakpoint 3 in foo: {{.+}}:14:24
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: sixth

test/debugger/fuzzy-break.js.debug

@@ -0,0 +1,7 @@
+break 12 1
+break 13 22
+break 14 200
+continue
+continue
+continue
+continue

test/debugger/fuzzy-lazy-oneline-break.js

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// RUN: %hdb --lazy %s < %s.debug | %FileCheck --match-full-lines %s
+// REQUIRES: debugger
+
+// @nolint
+function foo() { print('foo called'); /** * Some text to pad out the function so that it won't be eagerly compiled * for being too short. Lorem ipsum dolor sit amet, consectetur adipiscing * elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.  */ function bar() { print('bar called'); /** * Some text to pad out the function so that it won't be eagerly compiled * for being too short. Lorem ipsum dolor sit amet, consectetur adipiscing * elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.  */ } function baz() { print('baz called'); /** * Some text to pad out the function so that it won't be eagerly compiled * for being too short. Lorem ipsum dolor sit amet, consectetur adipiscing * elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.  */ }; bar(); baz(); }
+
+debugger;
+foo();
+
+/* This test verifies that you can set breakpoints in uncompiled
+ * functions, without fuzzy column matching accidentally resolving the
+ * breakpoint to the closest already-compiled instruction it can find.
+ * This comes up when debugging minified source with source maps.
+ */
+
+// CHECK: Break on 'debugger' statement in global: {{.*}}:14:1
+
+// Breakpoint is in the middle of the 'print' for 'bar called'
+// CHECK-NEXT: Set breakpoint 1 at {{.*}}:12:286
+// Breakpoint is in the middle of the 'print' for 'baz called'
+// CHECK-NEXT: Set breakpoint 2 at {{.*}}:12:556
+
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: foo called
+// CHECK-NEXT: Break on breakpoint 1 in bar: {{.*}}:12:286
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: bar called
+// CHECK-NEXT: Break on breakpoint 2 in baz: {{.*}}:12:556
+// CHECK-NEXT: Continuing execution
+// CHECK-NEXT: baz called

test/debugger/fuzzy-lazy-oneline-break.js.debug

@@ -0,0 +1,5 @@
+break 12 290
+break 12 560
+continue
+continue
+continue