6.3. dascov — Code Coverage

dascov is a command-line tool for measuring code coverage of daslang programs. It instruments code at compile time via daslib/coverage, runs it, and reports per-file, per-function, and branch coverage.

Quick start
Usage modes
- Instrument and measure
- LCOV summary
Output formats
- Brief summary (stdout)
- LCOV format (file)
Integration with dastest
Programmatic use

6.3.1. Quick start 

Measure coverage and print a brief summary:

daslang utils/dascov/main.das -- - path/to/script.das

Measure coverage and write an LCOV report:

daslang utils/dascov/main.das -- coverage.lcov path/to/script.das

View a summary of an existing LCOV file:

daslang utils/dascov/main.das -- coverage.lcov

6.3.2. Usage modes 

dascov has two modes of operation: instrument and measure (runs a daslang program with coverage enabled) and LCOV summary (parses an existing LCOV file and prints a summary).

6.3.2.1. Instrument and measure 

daslang utils/dascov/main.das -- <output> <input_file> [<args>...]

<output> – coverage destination:
- - – print a brief summary to stdout.
- <filename> – write a full LCOV-format report to the file.
<input_file> – the .das file to instrument and run.
<args> – any remaining arguments are forwarded to the target script as its command-line arguments.

dascov compiles the target file with coverage instrumentation enabled, runs its main function, then collects and outputs the results.

6.3.2.2. LCOV summary 

daslang utils/dascov/main.das -- <lcov_file> [--exclude <prefix>]...

Parses an existing LCOV coverage file (e.g. produced by dastest --cov-path) and prints a human-readable summary to stdout.

<lcov_file> – path to the LCOV file.
--exclude <prefix> – skip files whose path starts with prefix. Can be repeated to exclude multiple prefixes.

Example:

daslang utils/dascov/main.das -- coverage.lcov --exclude tests/ --exclude daslib/

6.3.3. Output formats 

6.3.3.1. Brief summary (stdout)

When the output is -, dascov prints a columnar summary with per-file and per-function hit/miss counts:

Coverage Summary
==============================================
File            Hits      Missed    Coverage
----------------------------------------------
main.das        3         1         75%
  main          3         1         75%
----------------------------------------------
TOTAL           3         1         75%

6.3.3.2. LCOV format (file)

When the output is a filename, dascov writes standard LCOV trace data. The format includes:

SF:<source_file> – source file path
FN:<line>,<function> – function definition
FNDA:<hits>,<function> – function hit count
FNF:<count> / FNH:<count> – functions found / hit
BRDA:<line>,<block>,<branch>,<hits> – branch data
BRF:<count> / BRH:<count> – branches found / hit
DA:<line>,<hits> – line hit count
LF:<count> / LH:<count> – lines found / hit

This output is compatible with standard LCOV tools, IDE coverage plugins, and CI/CD integrations.

6.3.4. Integration with dastest 

dastest can generate LCOV coverage data directly via the --cov-path flag:

daslang dastest/dastest.das -- --test tests/ --cov-path coverage.lcov

Each test file’s coverage is appended to the output file. After the run, use dascov to view a summary:

daslang utils/dascov/main.das -- coverage.lcov --exclude tests/

This workflow gives you coverage of your library code exercised by your test suite, excluding the test files themselves.

6.3.5. Programmatic use 

The underlying daslib/coverage module can be used directly in daslang code. Adding require daslib/coverage to a program enables compile-time coverage instrumentation via an [infer_macro].

Key functions:

fill_coverage_report(dest, name) – fill a string with LCOV data (for cross-context use via invoke_in_context).
fill_coverage_summary(dest, per_function) – fill a string with a brief summary.
summary_from_lcov_file(filename, excludes) – parse an LCOV file and return a summary string.