Terminal doesn't flush all line data before firing onExit

• VSCode Version: 1.43.0
• OS Version: Windows 10 version 1809
• Does this issue occur on the latest insiders build?: Yes
• Does this issue occur when all extensions are disabled?: Yes

Steps to Reproduce:

1. Create a Task which uses CustomExecution to output to a PseudoTerminal and specify one or more ProblemMatchers which are relevant to the Task’s output.
2. Run the Task. Its output seemingly will not be processed by the specified ProblemMatchers. At least, the effects are not applied - I cannot CTRL+click on file names, problems are not reported in the “Problems” tab, etc.

Sample code:

import * as vscode from "vscode";
import { exec } from "child_process";

// Simply run tsc and output the results to the terminal
class MyBuildTaskTerminal implements vscode.Pseudoterminal {
    private writeEmitter = new vscode.EventEmitter<string>();
    onDidWrite: vscode.Event<string> = this.writeEmitter.event;
    private closeEmitter = new vscode.EventEmitter<void>();
    onDidClose?: vscode.Event<void> = this.closeEmitter.event;

    open(_initialDimensions: vscode.TerminalDimensions | undefined): void {
        this.doBuild();
    }

    close(): void {
    }

    private async doBuild(): Promise<void> {
        this.writeEmitter.fire("Starting build...\r\n");

        // non-existent.ts doesn't exist and will output an error, but there will
        // be no corresponding entry in the "Problems" tab.
        //
        // Similarly, if the file did exist but contained errors (and I prefixed the
        // command with "cd /path/to/workspace/dir && "), I wouldn't be able
        // to CTRL+click the file's path to go to the location of the problem
        exec("tsc non-existent.ts", (_error, stdout, stderr) => {
            this.writeEmitter.fire(stdout);
            this.writeEmitter.fire(stderr);
            this.closeEmitter.fire();
        });
    }
}

const myTask = new vscode.Task(
    { type: "myType" },
    vscode.TaskScope.Workspace,
    "myTask",
    "mySource",
    new vscode.CustomExecution(async () => {
        // Pseudo-terminal implementing some task which fires onDidWrite()'s emitter
        // to output text. For this example, it runs tsc and outputs any compile errors
       return new MyBuildTaskTerminal();
    }),
    "$tsc"  // TypeScript errors should be picked up
);
vscode.tasks.executeTask(myTask);

VSCode behaves as expected if I change the line

new vscode.CustomExecution(...)

to

new vscode.ShellExecution("tsc non-existent.ts")

In my actual project, the Task’s logic is more complex and I can’t simply use ShellExecution.

[alexr00]

@Tyriar I added setTimeout hack so that my onLineData listener isn’t disposed until later, giving “enough” time after when exit is fired for the rest of the line data to come through.

[alexr00]

I modified the task provider sample to make a super simple example:

class CustomBuildTaskTerminal implements vscode.Pseudoterminal {
	private writeEmitter = new vscode.EventEmitter<string>();
	onDidWrite: vscode.Event<string> = this.writeEmitter.event;
	private closeEmitter = new vscode.EventEmitter<void>();
	onDidClose?: vscode.Event<void> = this.closeEmitter.event;

	open(initialDimensions: vscode.TerminalDimensions | undefined): void {
		this.doBuild();
	}

	close(): void {
	}

	private async doBuild(): Promise<void> {
		return new Promise<void>((resolve) => {
			this.writeEmitter.fire('src/customTaskProvider.ts:92:8 - error TS2551: Property \'doBuild\' does not exist on type \'CustomBuildTaskTerminal\'. Did you mean \'doBild\'?\r\n');
			this.writeEmitter.fire('\r\n');
			this.writeEmitter.fire('92      this.doBuild();\r\n');
			this.writeEmitter.fire('             ~~~~~~~\r\n');
			this.writeEmitter.fire('\r\n');
			this.writeEmitter.fire('  src/customTaskProvider.ts:99:16\r\n');
			this.writeEmitter.fire('    99  private async doBild(): Promise<void> {\r\n');
			this.writeEmitter.fire('                      ~~~~~~\r\n');
			this.writeEmitter.fire('\r\n');
			this.writeEmitter.fire('    \'doBild\' is declared here.\r\n');
			this.writeEmitter.fire('\r\n');
			this.writeEmitter.fire('\r\n');
			this.writeEmitter.fire('Found 1 error.');
			this.closeEmitter.fire();
		});
	}
}

Task for tasks.json:

        {
            "label": "custom with problem matcher",
            "type": "custombuildscript",
            "flavor": "32",
            "flags": [],
            "problemMatcher": "$tsc"
        }

When this runs without break points and with some logging, I can see that the the terminal is firing onExit before almost all of the onLineData. @Tyriar I thought there was something in place to prevent this now. How should I recommend folks handle this?