Make metric traits public

[Luni-4]

This PR makes all metric traits public. Code changes in this code have the following reasons:

• CodeMetricsT was only an aggregator of traits, better to declare metrics explicitly in Parser struct and ParserTrait removing a boilerplate layer
• Do not hide all code metric traits in documentation
• Add a macro that implements in a fake way unimplemented code metrics traits

We have decided to make all trait public in order to allow external users to compute metrics on single nodes since all arguments of the compute function are already public

[codecov-commenter]

Codecov Report

Patch coverage: 66.66% and project coverage change: -0.01 :warning:

Comparison is base (92f00bc) 74.18% compared to head (9b6a26f) 74.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1046 +/- ## ========================================== - Coverage 74.18% 74.18% -0.01% ========================================== Files 64 64 Lines 15923 15915 -8 ========================================== - Hits 11813 11807 -6 + Misses 4110 4108 -2 ``` | [Impacted Files](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | Coverage Δ | | |---|---|---| | [src/metrics/abc.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvYWJjLnJz) | `94.37% <ø> (-0.01%)` | :arrow_down: | | [src/metrics/cognitive.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvY29nbml0aXZlLnJz) | `99.28% <ø> (-0.01%)` | :arrow_down: | | [src/metrics/cyclomatic.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvY3ljbG9tYXRpYy5ycw==) | `96.96% <ø> (+0.20%)` | :arrow_up: | | [src/metrics/exit.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvZXhpdC5ycw==) | `96.04% <ø> (+0.34%)` | :arrow_up: | | [src/metrics/halstead.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvaGFsc3RlYWQucnM=) | `93.38% <ø> (+0.18%)` | :arrow_up: | | [src/metrics/loc.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvbG9jLnJz) | `98.98% <ø> (+0.03%)` | :arrow_up: | | [src/metrics/mi.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvbWkucnM=) | `87.14% <ø> (ø)` | | | [src/metrics/nargs.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvbmFyZ3MucnM=) | `97.86% <ø> (ø)` | | | [src/metrics/nom.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3Mvbm9tLnJz) | `95.70% <ø> (ø)` | | | [src/metrics/npa.rs](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla#diff-c3JjL21ldHJpY3MvbnBhLnJz) | `97.25% <ø> (-0.01%)` | :arrow_down: | | ... and [4 more](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla) | | ... and [1 file with indirect coverage changes](https://codecov.io/gh/mozilla/rust-code-analysis/pull/1046/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mozilla)

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[marco-c]

I'm OK with these changes, except the last two commits that do Add a macro that implements in a fake way unimplemented code metrics traits. What is the benefit of this?

[Luni-4]

Without that macro, we should add {} to the trait definition not to have a compiler error on the implementations. In this way instead:

• We have a clean definition with a correct documentation (since traits are now public)
• If a code language does not implement a trait, the compiler immediately raises an error

[marco-c]

Are you sure we don't achieve the same two results if we stop at commit 232f502b60017f8eeea4a799434425470cc92e66? Isn't impl Abc for PythonCode {} already giving us an error if a language doesn't implement a trait?

[Luni-4]

Are you sure we don't achieve the same two results if we stop at commit 232f502? Isn't impl Abc for PythonCode {} already giving us an error if a language doesn't implement a trait?

Yes, we already have an error but because of this line, since we require to have Abc trait implemented for PythonCode in order to allow Parser<PythonCode>. To better explain my position: using a trait with a default implementation does not create a clear documentation and leads to lose the distinctions among metric implementations for each language

[marco-c]

Could you show me the difference in generated documentation? I want to understand the result better before accepting the second part of the changes (I'm happy to merge the first part right away if you create that as a separate PR).

[Luni-4]

Yep, loading the two documentations to show the main differences

Documentation without the second part

Documentation with the second part

The main differences are:

• No empty implementation within the trait, just the function signature
• No unused variable warnings due to the empty implementation, so the removal of _ from function arguments

For what concerns the error I was talking about instead:

Commenting PythonCode implementation on master for abc metric

error[E0277]: the trait bound `langs::PythonCode: metrics::abc::Abc` is not satisfied
   --> src/macros.rs:225:45
    |
225 |               impl _private::CodeMetricsT for $code { }
    |                                               ^^^^^ the trait `metrics::abc::Abc` is not implemented for `langs::PythonCode`
    |
   ::: src/langs.rs:8:1
    |
8   | / mk_langs!(
9   | |     // 1) Name for enum
10  | |     // 2) Language description
11  | |     // 3) Display name
...   |
126 | |     )
127 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `metrics::abc::Abc`:
              langs::CcommentCode
              langs::CppCode
              langs::JavaCode
              langs::JavascriptCode
              langs::KotlinCode
              langs::MozjsCode
              langs::PreprocCode
              langs::RustCode
            and 2 others
note: required by a bound in `CodeMetricsT`
   --> src/traits.rs:43:83
    |
42  |     pub trait CodeMetricsT:
    |               ------------ required by a bound in this trait
43  |         Cognitive + Cyclomatic + Exit + Halstead + NArgs + Loc + Nom + Mi + Wmc + Abc + Npm + Npa
    |                                                                                   ^^^ required by this bound in `CodeMetricsT`
    = note: this error originates in the macro `mk_code` which comes from the expansion of the macro `mk_langs` (in Nightly builds, run with -Z macro-backtrace for more info)

For more information about this error, try `rustc --explain E0277`.
error: could not compile `rust-code-analysis` due to previous error

Commenting PythonCode implementation on this PR for abc metric

error[E0277]: the trait bound `langs::PythonCode: Abc` is not satisfied
   --> src/macros.rs:207:38
    |
207 |                           let parser = $parser::new(source, &path, pr);
    |                                        ^ the trait `Abc` is not implemented for `langs::PythonCode`
    |
   ::: src/langs.rs:8:1
    |
8   | / mk_langs!(
9   | |     // 1) Name for enum
10  | |     // 2) Language description
11  | |     // 3) Display name
...   |
126 | |     )
127 | | );
    | |_- in this macro invocation
    |
    = help: the following other types implement trait `Abc`:
              langs::CcommentCode
              langs::CppCode
              langs::JavaCode
              langs::JavascriptCode
              langs::KotlinCode
              langs::MozjsCode
              langs::PreprocCode
              langs::RustCode
            and 2 others
note: required by a bound in `parser::Parser`
   --> src/parser.rs:34:11
    |
29  | pub struct Parser<
    |            ------ required by a bound in this struct
...
34  |         + Abc
    |           ^^^ required by this bound in `Parser`
    = note: this error originates in the macro `mk_action` which comes from the expansion of the macro `mk_langs` (in Nightly builds, run with -Z macro-backtrace for more info)

The main difference is that the error is now associated to the Parser struct and not to the CodeMetricsT trait implementation