Allow attaching (remote and local) with no program

There is no strict need to have a program passed to GDB when
attaching (remote or local). Either the program can be downloaded
from the remote or otherwise read by GDB, or if not possible
then GDB can do symbol-free debugging.

Previously in eclipse-cdt-cloud#228 some work was done to better error when
program was not specified. This change loosens the restrictions
slightly. If the program is not specified, it is still a warning
in VSCode because of
[package.json](https://github.com/eclipse-cdt-cloud/cdt-gdb-vscode/blob/22a9f1048f9030689ed1f5f2b3e5d5e48df9047d/package.json#L205-L207)

See this comment for how it is presented to a user:
eclipse-cdt-cloud#261 (comment)

Part of eclipse-cdt-cloud#261

src/GDBDebugSession.ts

@@ -338,15 +338,19 @@ export class GDBDebugSession extends LoggingDebugSession {
         );
 
         await this.spawn(args);
-        if (!args.program) {
-            this.sendErrorResponse(
-                response,
-                1,
-                'The program must be specified in the request arguments'
-            );
-            return;
+        if (request == 'launch') {
+            if (!args.program) {
+                this.sendErrorResponse(
+                    response,
+                    1,
+                    'The program must be specified in the request arguments'
+                );
+                return;
+            }
+        }
+        if (args.program) {
+            await this.gdb.sendFileExecAndSymbols(args.program);
         }
-        await this.gdb.sendFileExecAndSymbols(args.program);
         await this.gdb.sendEnablePrettyPrint();
 
         if (request === 'attach') {
@@ -997,7 +1001,7 @@ export class GDBDebugSession extends LoggingDebugSession {
             }
             response.body = {
                 allThreadsContinued: isAllThreadsContinued,
-            }
+            };
             this.sendResponse(response);
         } catch (err) {
             this.sendErrorResponse(

src/GDBTargetDebugSession.ts

@@ -275,7 +275,9 @@ export class GDBTargetDebugSession extends GDBDebugSession {
         try {
             this.isAttach = true;
             await this.spawn(args);
-            await this.gdb.sendFileExecAndSymbols(args.program);
+            if (args.program) {
+                await this.gdb.sendFileExecAndSymbols(args.program);
+            }
             await this.gdb.sendEnablePrettyPrint();
             if (args.imageAndSymbols) {
                 if (args.imageAndSymbols.symbolFileName) {

src/integration-tests/attach.spec.ts

@@ -51,4 +51,17 @@ describe('attach', function () {
         await dc.attachHitBreakpoint(attachArgs, { line: 25, path: src });
         expect(await dc.evaluate('argv[1]')).to.contain('running-from-spawn');
     });
+
+    it('can attach and hit a breakpoint with no program specified', async function () {
+        if (isRemoteTest) {
+            // attachRemote.spec.ts is the test for when isRemoteTest
+            this.skip();
+        }
+
+        const attachArgs = fillDefaults(this.test, {
+            processId: `${inferior.pid}`,
+        } as AttachRequestArguments);
+        await dc.attachHitBreakpoint(attachArgs, { line: 25, path: src });
+        expect(await dc.evaluate('argv[1]')).to.contain('running-from-spawn');
+    });
 });

src/integration-tests/attachRemote.spec.ts

@@ -10,6 +10,7 @@
 
 import * as cp from 'child_process';
 import * as path from 'path';
+import * as os from 'os';
 import {
     TargetAttachRequestArguments,
     TargetAttachArguments,
@@ -74,4 +75,19 @@ describe('attach remote', function () {
         await dc.attachHitBreakpoint(attachArgs, { line: 3, path: emptySrc });
         expect(await dc.evaluate('argv[1]')).to.contain('running-from-spawn');
     });
+
+    it('can attach remote and hit a breakpoint without a program', async function () {
+        if (os.platform() === 'win32') {
+            // win32 host does support this use case
+            this.skip();
+        }
+        const attachArgs = fillDefaults(this.test, {
+            target: {
+                type: 'remote',
+                parameters: [`localhost:${port}`],
+            } as TargetAttachArguments,
+        } as TargetAttachRequestArguments);
+        await dc.attachHitBreakpoint(attachArgs, { line: 3, path: emptySrc });
+        expect(await dc.evaluate('argv[1]')).to.contain('running-from-spawn');
+    });
 });