[lldb][swift] Filter Q funclets when setting breakpoints

These funclets only serve to `task_dealloc` previously allocated tasks when
returning from an async call, and immediately `task_switch` to the next
await-suspend funclet (which contains real user code).

By not filtering out these funclets, any breakpoint on a line with an async call
will cause execution to pause 3 times: once before the call, twice when
"returning" from the call, which makes for a confusing experience.

The patch does the filtering on `BreakpointResolver::SetSCMatchesByLine`, which
is the common code between BreakpointResolverFileLine and
BreakpointResolverFileRegex.

We also considered changing the debug line information in any of the many
different lowering stages the swift compiler, but this turned out to be very
complex to do in a targeted way; more often than not, a handful of early-IR
coroutine instructions get expanded into multiple function clones, all
inheriting the same debug line information. The current approach also has the
advantaged of being easily reversible if we decide to do so.

Author: felipepiovezan

lldb/source/Plugins/Language/Swift/SwiftLanguage.cpp

@@ -1814,6 +1814,17 @@ SwiftLanguage::GetDemangledFunctionNameWithoutArguments(Mangled mangled) const {
   return mangled_name;
 }
 
+bool SwiftLanguage::IgnoreForLineBreakpoints(const SymbolContext &sc) const {
+  // If we don't have a function, conservatively return false.
+  if (!sc.function)
+    return false;
+  StringRef name = sc.function->GetMangled().GetMangledName().GetStringRef();
+  // In async functions, ignore await resume ("Q") funclets, these only
+  // deallocate the async context and task_switch back to user code.
+  return SwiftLanguageRuntime::IsSwiftAsyncAwaitResumePartialFunctionSymbol(
+      name);
+}
+
 //------------------------------------------------------------------
 // Static Functions
 //------------------------------------------------------------------

lldb/source/Plugins/Language/Swift/SwiftLanguage.h

@@ -90,6 +90,9 @@ class SwiftLanguage : public Language {
 
   llvm::StringRef GetInstanceVariableName() override { return "self"; }
 
+  /// Override that skips breakpoints inside await resume ("Q") async funclets.
+  bool IgnoreForLineBreakpoints(const SymbolContext &sc) const override;
+
   //------------------------------------------------------------------
   // PluginInterface protocol
   //------------------------------------------------------------------

lldb/test/API/lang/swift/async_breakpoints/Makefile

@@ -0,0 +1,3 @@
+SWIFT_SOURCES := main.swift
+
+include Makefile.rules

lldb/test/API/lang/swift/async_breakpoints/TestSwiftAsyncBreakpoints.py

@@ -0,0 +1,54 @@
+import lldb
+from lldbsuite.test.decorators import *
+import lldbsuite.test.lldbtest as lldbtest
+import lldbsuite.test.lldbutil as lldbutil
+
+
+class TestSwiftAsyncBreakpoints(lldbtest.TestBase):
+    @swiftTest
+    @skipIfWindows
+    @skipIfLinux
+    @skipIf(archs=no_match(["arm64", "arm64e", "x86_64"]))
+    def test(self):
+        """Test async breakpoints"""
+        self.build()
+        filespec = lldb.SBFileSpec("main.swift")
+        target, process, thread, breakpoint1 = lldbutil.run_to_source_breakpoint(
+            self, "Breakpoint1", filespec
+        )
+        breakpoint2 = target.BreakpointCreateBySourceRegex("Breakpoint2", filespec)
+        breakpoint3 = target.BreakpointCreateBySourceRegex("Breakpoint3", filespec)
+        self.assertEquals(breakpoint1.GetNumLocations(), 2)
+        self.assertEquals(breakpoint2.GetNumLocations(), 1)
+        self.assertEquals(breakpoint3.GetNumLocations(), 2)
+
+        location11 = breakpoint1.GetLocationAtIndex(0)
+        location12 = breakpoint1.GetLocationAtIndex(1)
+        self.assertEquals(location11.GetHitCount(), 1)
+        self.assertEquals(location12.GetHitCount(), 0)
+
+        self.assertEquals(thread.GetStopDescription(128), "breakpoint 1.1")
+        process.Continue()
+        self.assertEquals(thread.GetStopDescription(128), "breakpoint 1.2")
+
+        thread.StepOver()
+        self.assertEquals(thread.GetStopDescription(128), "breakpoint 2.1")
+        self.expect("expr timestamp1", substrs=["42"])
+
+        thread.StepOver()
+        self.assertIn("breakpoint 3.1", thread.GetStopDescription(128))
+        self.expect("expr timestamp1", substrs=["42"])
+
+        process.Continue()
+        self.assertIn("breakpoint 3.2", thread.GetStopDescription(128))
+        self.expect("expr timestamp1", substrs=["42"])
+
+        thread.StepOver()
+        self.expect("expr timestamp1", substrs=["42"])
+        self.expect("expr timestamp2", substrs=["43"])
+
+        self.runCmd("settings set language.enable-filter-for-line-breakpoints false")
+        breakpoint1_no_filter = target.BreakpointCreateBySourceRegex(
+            "Breakpoint1", filespec
+        )
+        self.assertEquals(breakpoint1_no_filter.GetNumLocations(), 3)

lldb/test/API/lang/swift/async_breakpoints/main.swift

@@ -0,0 +1,15 @@
+func getTimestamp(i:Int) async -> Int {
+  return i
+}
+
+func work() {}
+
+func foo() async {
+  work()
+  let timestamp1 = await getTimestamp(i:42) // Breakpoint1
+  work() // Breakpoint2
+  let timestamp2 = await getTimestamp(i:43) // Breakpoint3
+  work()
+}
+
+await foo()