#10027 Support EvaluatableExpressions

[ndoschek]

What it does

• Implement support for plugins providing evalutable epressions
• Update the debug hover widget to consume evaluatable expressions from the registered providers. Keep the former implementation of guessing the expression from the current line as fallback.

Contributed on behalf of STMicroelectronics

Signed-off-by: Nina Doschek ndoschek@eclipsesource.com

Fixes #10027

How to test

To test, I created a simple evalutable expression provider for the java language, available via the custom vscode extension: evaluatable-expression-extension-10027-0.0.1.zip

1. Install the extensions Language Support for Java(TM) by Red Hat (identifier: redhat.java) and Debugger for Java (identifier: vscjava.vscode-java-debug) from the Open VSX Registry (Extensions view) in your Theia test workspace.
   On startup, it will show an information message that the provider was registered.
2. Download and install the test extension evaluatable-expression-extension-10027.vsix in your Theia test workspace (via Extensions view - top menu bar More actions... - Install from VSIX).
3. Create a simple Java application to debug

Simple Test application

package myproject;

public class Test {

    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {
            String logMessage = "logging a message for i=" + i;
            System.out.println(logMessage);
        }
    }
}

4. Set a breakpoint in line 8 (sysout) and launch the file debugging

Launch config

 {
   "type": "java",
   "name": "Launch Current File",
   "request": "launch",
   "mainClass": "${file}"
 }

5. Once the breakpoint is hit, hover over the local variable logMessage, the extension shows an information message with the cursor position and the provided word range of the expression.
   e.g. [TestEvaluatableExpressionExtension] provide word range for position { "line": 6, "character": 26 } > [ { "line": 6, "character": 19 }, { "line": 6, "character": 29 } ]

Review checklist

• As an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• As a reviewer, I agree to behave in accordance with the review guidelines

[colin-grant-work]

I believe the implementation is correct, but while testing, I discovered a problem with the implementation of our DebugHoverWidget. I tested this PR using this plugin and this debugger with the InlineValueProvider code removed to allow it to activate.

As far as I can tell, all of the EvaluatableExpression code ran as expected - the plugin code was called, the returns were correct - but the DebugHoverWidget never appeared. It seems that when this code runs

theia/packages/debug/src/browser/editor/debug-hover-source.tsx

Lines 49 to 56 in 0c0f8c7

	async evaluate(expression: string): Promise<ExpressionItem | DebugVariable | undefined> {
	const evaluated = await this.doEvaluate(expression);
	const elements = evaluated && await evaluated.getElements();
	this._expression = evaluated;
	this.elements = elements ? [...elements] : [];
	this.fireDidChange();
	return evaluated;
	}

elements is undefined, and so there is nothing to render when the DebugHoverWidget requests elements

theia/packages/debug/src/browser/editor/debug-hover-source.tsx

Lines 35 to 37 in 0c0f8c7

	getElements(): IterableIterator<TreeElement> {
	return this.elements[Symbol.iterator]();
	}

and so the DebugHoverWidget does not appear. In VSCode, by contrast, the widget does appear and renders the text as returned by the debugger.

[ndoschek]

Thanks for your comments @colin-grant-work!
Regarding the minor ones, I updated my commit accordingly.

About the mock debug extension, I have a more general problem, that it does not work as properly as in VSCode for me, i.e. it does not hit breakpoints and a debug session cannot be exited/terminated. It is stuck on the last line of any markdown file after hitting Continue and does not respond to the Stop button. Stepping however works, and in that case I can confirm your observation that the debug widget does not appear.
I used the current master of the mock debug extension, and omitted the provideInlineValues command as you described.
Is there something I'm missing?

As I mentioned in the description, for the Java case, the debugging session and the hover widget are working fine for me.

[colin-grant-work]

@ndoschek, I see the problems you mention - I'm not sure what's going on there, and it should be investigated elsewhere - but it looks like it's still possible to step though, so it's possible to stop on any line you'd like, even without a breakpoint. The inability to exit the session is a bummer. I tried moving back to commit 553fbf61c7d42d9c77ead3fdcb8bc134fef11677 (and removing the InlineValueProvider code), and the same problem with breakpoints is present, but the session at least doesn't seem to crash and be unkillable at the end of the file.

[ndoschek]

Thanks @colin-grant-work, that's way better now, I'll have another look at the mentioned issue!

[colin-grant-work]

@ndoschek, I definitely think that the problems with the hover widget ought to be fixed, and the problems with the mock debug extension investigated, but in principle both are separate from the work you've done. If you'd prefer to pursue the fix for the hover widget in a separate PR, I think the plugin side of this PR is correct and complete and could be merged.

[ndoschek]

Hi @colin-grant-work,
Thanks for your input, I had another look at the causes of the issues with the mock debug extension, and it is not yet fully clear to me what the actual cause is. Hence, I would prefer to separate those two concerns, as the support of EvaluatableExpressions via plugins is available now with this PR.
I created a separate issue for the formerly discussed issue here: #11500

[colin-grant-work]

The implementation of the EvaluatableExpressionProvider API is complete and correct. 👍