Add step back support for DAP

The step back button is hidden because most dap implementations don't support
it.

crates/debugger_ui/src/debugger_panel_item.rs

@@ -588,6 +588,18 @@ impl DebugPanelItem {
         });
     }
 
+    pub fn step_back(&mut self, cx: &mut ViewContext<Self>) {
+        self.update_thread_state_status(ThreadStatus::Running, cx);
+
+        let granularity = DebuggerSettings::get_global(cx).stepping_granularity;
+
+        self.dap_store.update(cx, |store, cx| {
+            store
+                .step_back(&self.client_id, self.thread_id, granularity, cx)
+                .detach_and_log_err(cx);
+        });
+    }
+
     pub fn restart_client(&self, cx: &mut ViewContext<Self>) {
         self.dap_store.update(cx, |store, cx| {
             store
@@ -807,6 +819,17 @@ impl Render for DebugPanelItem {
                                     .disabled(thread_status != ThreadStatus::Stopped)
                                     .tooltip(move |cx| Tooltip::text("Step out", cx)),
                             )
+                            .when(capabilities.supports_step_back.unwrap_or(false), |this| {
+                                this.child(
+                                    IconButton::new("debug-step-back", IconName::DebugStepBack)
+                                        .icon_size(IconSize::Small)
+                                        .on_click(cx.listener(|this, _, cx| {
+                                            this.step_back(cx);
+                                        }))
+                                        .disabled(thread_status != ThreadStatus::Stopped)
+                                        .tooltip(move |cx| Tooltip::text("Step back", cx)),
+                                )
+                            })
                             .child(
                                 IconButton::new("debug-restart", IconName::DebugRestart)
                                     .icon_size(IconSize::Small)

crates/project/src/dap_store.rs

@@ -3,15 +3,15 @@ use crate::{ProjectEnvironment, ProjectItem as _, ProjectPath};
 use anyhow::{anyhow, Context as _, Result};
 use async_trait::async_trait;
 use collections::HashMap;
-use dap::adapters::{DapDelegate, DapStatus, DebugAdapter, DebugAdapterBinary, DebugAdapterName};
 use dap::{
+    adapters::{DapDelegate, DapStatus, DebugAdapter, DebugAdapterBinary, DebugAdapterName},
     client::{DebugAdapterClient, DebugAdapterClientId},
     messages::{Message, Response},
     requests::{
         Attach, Completions, ConfigurationDone, Continue, Disconnect, Evaluate, Initialize, Launch,
         LoadedSources, Modules, Next, Pause, Request as _, Restart, RunInTerminal, Scopes,
-        SetBreakpoints, SetExpression, SetVariable, StackTrace, StartDebugging, StepIn, StepOut,
-        Terminate, TerminateThreads, Variables,
+        SetBreakpoints, SetExpression, SetVariable, StackTrace, StartDebugging, StepBack, StepIn,
+        StepOut, Terminate, TerminateThreads, Variables,
     },
     AttachRequestArguments, Capabilities, CompletionItem, CompletionsArguments,
     ConfigurationDoneArguments, ContinueArguments, DisconnectArguments, ErrorResponse,
@@ -20,8 +20,9 @@ use dap::{
     ModulesArguments, NextArguments, PauseArguments, RestartArguments, RunInTerminalResponse,
     Scope, ScopesArguments, SetBreakpointsArguments, SetExpressionArguments, SetVariableArguments,
     Source, SourceBreakpoint, StackFrame, StackTraceArguments, StartDebuggingRequestArguments,
-    StartDebuggingRequestArgumentsRequest, StepInArguments, StepOutArguments, SteppingGranularity,
-    TerminateArguments, TerminateThreadsArguments, Variable, VariablesArguments,
+    StartDebuggingRequestArgumentsRequest, StepBackArguments, StepInArguments, StepOutArguments,
+    SteppingGranularity, TerminateArguments, TerminateThreadsArguments, Variable,
+    VariablesArguments,
 };
 use dap_adapters::build_adapter;
 use fs::Fs;
@@ -1077,6 +1078,37 @@ impl DapStore {
         })
     }
 
+    pub fn step_back(
+        &self,
+        client_id: &DebugAdapterClientId,
+        thread_id: u64,
+        granularity: SteppingGranularity,
+        cx: &mut ModelContext<Self>,
+    ) -> Task<Result<()>> {
+        let Some(client) = self.client_by_id(client_id) else {
+            return Task::ready(Err(anyhow!("Could not find client: {:?}", client_id)));
+        };
+
+        let capabilities = self.capabilities_by_id(client_id);
+
+        let supports_single_thread_execution_requests = capabilities
+            .supports_single_thread_execution_requests
+            .unwrap_or_default();
+        let supports_stepping_granularity = capabilities
+            .supports_stepping_granularity
+            .unwrap_or_default();
+
+        cx.background_executor().spawn(async move {
+            client
+                .request::<StepBack>(StepBackArguments {
+                    thread_id,
+                    granularity: supports_stepping_granularity.then(|| granularity),
+                    single_thread: supports_single_thread_execution_requests.then(|| true),
+                })
+                .await
+        })
+    }
+
     pub fn variables(
         &self,
         client_id: &DebugAdapterClientId,

crates/ui/src/components/icon.rs

@@ -168,6 +168,7 @@ pub enum IconName {
     DebugStepOver,
     DebugStepInto,
     DebugStepOut,
+    DebugStepBack,
     DebugRestart,
     Debug,
     DebugStop,