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v0-changes.md

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Changes from the v0 instrumenter

Differences in instrumentation

  • Function declarations and variable declarations are not treated as statements.
  • However, each individual variable declaration that is also initialized becomes a statement that is tracked.
  • Class methods and arrow functions now contribute to function coverage.
  • Assignment expressions (i.e. default arguments assigned to function params) now count as a branch.
  • Ignore now really means "do not instrument". Previously, ignore code would still generate coverage counters with additional metadata for reporting to ignore them. Now, nothing is injected when ignores are in effect; this fixes issues with people wanting to ignore functions and ship them over the wire to a different execution environment where the coverage variables are not defined. It also means that the HTML report will be unable to show how many statements/ functions/ branches were ignored.
  • Internally uses babel rather than esprima and exports a new visitor that can be used by a babel plugin to instrument the ES6 code without having to instrument transpiled code and deal with source maps. This provides a "native" instrumentation option for Babel users.

API changes

  • instrumenter.instrumentASTSync is no longer supported. It was a bad idea to expose this in the first place. The AST is different (a Babel AST) now and this fact is now correctly hidden in the implementation of the API so that future changes to the AST is possible without affecting consumers.
  • Instrumenter options:
    • embedSource no longer available. The original source is never packed in with the coverage object. This was causing all manner of special casing in the reporting code.
    • noAutoWrap becomes autoWrap (default false). Mainline return statements are no longer considered correct by default.
    • codeGenerationOptions is gone. This was specific to escodegen that is no longer used.
    • walkDebug option is gone now that babel does the AST walking
    • produceSourceMap boolean option added to produce a source map for the instrumented code. This is available using the lastSourceMap method on the instrumenter (as before, except that the mechanism to turn it on is direct and not a property passed down to escodegen)
    • sourceMapUrlCallback may be set to a function that accepts 2 arguments, the source file name and the source map URL found in it.