name: add-diagnostic-parser description: > Use when adding a compiler or tool output parser for the Problems panel. Touches src/diagnostics/<name>.ts, src/diagnostics/build.ts, package.json (cmake.enabledOutputParsers), and package.nls.json. Triggers: "add parser", "new diagnostic parser", "parse compiler output".

Adding a New Diagnostic / Output Parser

Recipe for adding a new compiler or tool output parser to CMake Tools. A parser extracts diagnostics (errors, warnings, notes) from build output and surfaces them in the VS Code Problems panel.

Overview

Adding a parser touches 4 files (plus tests and changelog):

Step 1: Create the parser file

Create src/diagnostics/<name>.ts. Every parser extends RawDiagnosticParser (defined in src/diagnostics/util.ts) and exports a class named Parser.

Base class contract

// src/diagnostics/util.ts (simplified)
export abstract class RawDiagnosticParser {
    get diagnostics(): readonly RawDiagnostic[] { /* accumulated results */ }

    /** Called by the build consumer for every line of output. */
    handleLine(line: string): boolean {
        const result = this.doHandleLine(line);
        if (result === FeedLineResult.Ok) return true;        // line consumed, no new diagnostic
        if (result === FeedLineResult.NotMine) return false;   // line not recognized
        // Otherwise result is a RawDiagnostic — it gets stored automatically
        this._diagnostics.push(result);
        return true;
    }

    /** Implement this. Return a RawDiagnostic to emit, or a FeedLineResult. */
    protected abstract doHandleLine(line: string): RawDiagnostic | FeedLineResult;
}

Minimal single-regex parser (like MSVC)

/**
 * Module for parsing <ToolName> diagnostics
 */ /** */

import * as vscode from 'vscode';
import { oneLess, RawDiagnosticParser, FeedLineResult } from '@cmt/diagnostics/util';

// Regex that captures: file, line, severity, code (optional), message
export const REGEX = /^(.+):(\d+):\s+(error|warning|info)\s+(\w+):\s+(.*)$/;

export class Parser extends RawDiagnosticParser {
    doHandleLine(line: string) {
        const mat = REGEX.exec(line);
        if (!mat) {
            return FeedLineResult.NotMine;
        }
        const [full, file, lineStr, severity, code, message] = mat;
        const lineno = oneLess(lineStr);   // convert 1-based to 0-based
        return {
            full,
            file,
            location: new vscode.Range(lineno, 0, lineno, 999),
            severity,
            message,
            code,
            related: []
        };
    }
}

Multi-line / stateful parser (like IAR)

For tools whose diagnostics span multiple lines, use internal state:

import { RawDiagnosticParser, RawDiagnostic, FeedLineResult, oneLess } from '@cmt/diagnostics/util';

enum ParserState { init, pending_message }

export class Parser extends RawDiagnosticParser {
    private state = ParserState.init;
    private pending: RawDiagnostic | null = null;

    doHandleLine(line: string): RawDiagnostic | FeedLineResult {
        switch (this.state) {
            case ParserState.init: {
                const mat = FIRST_LINE_REGEX.exec(line);
                if (!mat) return FeedLineResult.NotMine;
                this.pending = { /* ... build partial diagnostic ... */ };
                this.state = ParserState.pending_message;
                return FeedLineResult.Ok;  // consumed, but not complete yet
            }
            case ParserState.pending_message: {
                if (/* line completes the diagnostic */) {
                    const diag = this.pending!;
                    this.reset();
                    return diag;           // emits the diagnostic
                }
                return FeedLineResult.Ok;  // still accumulating
            }
        }
        return FeedLineResult.NotMine;
    }
}

Key types

// src/diagnostics/util.ts
interface RawDiagnostic {
    full: string;               // the full matched line(s)
    file: string;               // source file path
    location: vscode.Range;     // 0-based range (use oneLess() for 1-based input)
    severity: string;           // 'error' | 'warning' | 'note' | 'info' | 'fatal error' | 'remark'
    message: string;
    code?: string;              // optional diagnostic code (e.g. 'C4996', 'LNK2019')
    related: RawRelated[];      // related diagnostics (notes, template backtraces)
}

enum FeedLineResult {
    Ok,       // line was consumed (but no new diagnostic produced yet)
    NotMine,  // line not recognized by this parser
}

diagnosticSeverity() in util.ts maps the severity string to vscode.DiagnosticSeverity. Recognized values: 'error', 'fatal error', 'catastrophic error', 'warning', 'note', 'info', 'remark'.

Step 2: Register in src/diagnostics/build.ts

Import the new parser module and add an instance to the Compilers class. The property name becomes the parser identifier used in cmake.enabledOutputParsers.

// At the top — add import
import * as myparser from '@cmt/diagnostics/myparser';

// Inside the Compilers class — add property
export class Compilers {
    [compiler: string]: RawDiagnosticParser;

    gcc = new gcc.Parser();
    gnuld = new gnu_ld.Parser();
    ghs = new ghs.Parser();
    diab = new diab.Parser();
    msvc = new mvsc.Parser();
    iar = new iar.Parser();
    iwyu = new iwyu.Parser();
    myparser = new myparser.Parser();   // ← new parser
}

The CompileOutputConsumer.error() method iterates over all Compilers properties in declaration order, calling parser.handleLine(line). The first parser to return true claims the line — order matters if your parser's regex could match lines from another compiler.

The resolveDiagnostics() method filters diagnostics by config.enableOutputParsers — only parsers whose name appears in that array will have their diagnostics shown in the Problems panel.

Step 3: Update package.json

Add the parser name to the cmake.enabledOutputParsers enum. Decide whether it should be default-enabled or opt-in.

// package.json → contributes.configuration → cmake.enabledOutputParsers
"cmake.enabledOutputParsers": {
    "type": "array",
    "items": {
        "type": "string",
        "enum": [
            "cmake",
            "gcc",
            "gnuld",
            "msvc",
            "ghs",
            "diab",
            "iar",
            "iwyu",
            "myparser"     // ← add to enum
        ]
    },
    "default": [
        "cmake",
        "gcc",
        "gnuld",
        "msvc",
        "ghs",
        "diab"
        // only add here if default-enabled
    ]
}

Step 4: Update package.nls.json

If any user-visible setting descriptions changed, update the localization key in package.nls.json. The cmake.enabledOutputParsers description uses the key cmake-tools.configuration.cmake.enabledOutputParsers.description.

Step 5: Write tests

Add tests in test/unit-tests/diagnostics.test.ts. The test pattern:

test('Parse <tool> error', () => {
    const build_consumer = new diags.CompileOutputConsumer(
        new ConfigurationReader({} as ExtensionConfigurationSettings)
    );
    // Feed real compiler output lines
    build_consumer.error('<tool-specific output line>');

    // Verify diagnostics
    const parser = build_consumer.compilers.myparser;
    expect(parser.diagnostics).to.have.length(1);
    expect(parser.diagnostics[0].severity).to.eq('error');
    expect(parser.diagnostics[0].file).to.eq('expected/file.cpp');
});

Step 6: CHANGELOG.md

Add an entry under the current version:

Features:
- Add `myparser` diagnostic parser for <ToolName> compiler output. [PR #XXXX](https://github.com/microsoft/vscode-cmake-tools/pull/XXXX)

Currently registered parsers

The cmake parser (in src/diagnostics/cmake.ts) is separate — it handles CMake's own configure/generate output via CMakeOutputConsumer, not build compiler output. It is listed in the enabledOutputParsers default array but is not part of the Compilers class.

Default-enabled vs opt-in

• Default-enabled parsers (cmake, gcc, gnuld, msvc, ghs, diab) are included in the "default" array in package.json. Users get them automatically.
• Opt-in parsers (iar, iwyu) are in the "enum" but not in "default". Users must add them to their cmake.enabledOutputParsers setting.
• Use opt-in for parsers with aggressive regexes that might false-positive on common output, or for niche toolchains.

Verification checklist

• Parser class extends RawDiagnosticParser and exports as Parser
• doHandleLine() returns FeedLineResult.NotMine for unrecognized lines
• doHandleLine() returns a RawDiagnostic (not FeedLineResult.Ok) when a diagnostic is complete
• Line/column numbers converted from 1-based to 0-based with oneLess()
• Registered in Compilers class in src/diagnostics/build.ts
• Added to cmake.enabledOutputParsers enum in package.json
• Default array updated (or deliberately left opt-in)
• Unit tests in test/unit-tests/diagnostics.test.ts pass
• yarn compile succeeds
• CHANGELOG.md entry added

See also: .github/copilot-instructions.md for project-wide conventions.