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Merge pull request #585 from robinmaisch/rust
Add Rust frontend
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| # JPlag Rust language frontend | ||
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| The JPlag Rust frontend allows the use of JPlag with submissions in Scala. <br> | ||
| It is based on the [Rust ANTLR4 grammar](https://github.com/antlr/grammars-v4/tree/master/rust), licensed under MIT. | ||
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| ### Rust specification compatibility | ||
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| According to the grammar's documentation, it was updated to Rust 1.60.0 (April 2022). | ||
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| ### Token Extraction | ||
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| #### General | ||
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| The choice of tokens is intended to be similar to the Java or C# frontends. Specifically, among others, it includes a | ||
| range of nesting structures (class and method declarations, control flow expressions) as well as variable declaration, | ||
| object creation, assignment, and control flow altering keywords. <br> | ||
| Blocks are distinguished by their context, i.e. there are separate `TokenConstants` for `if` blocks, `for` blocks, class | ||
| bodies, method bodies, array constructors, and the like. | ||
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| More syntactic elements of Rust may turn out to be helpful to include in the future, especially those that are newly | ||
| introduced. | ||
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| #### Problem in Rust (1): Grammar formulation | ||
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| In contrast to other grammars used in frontends, the underlying Rust ANTLR4 grammar uses very general syntactic categories | ||
| that do not provide very much _semantic_ information. For example, the ifExpression rule features a `blockExpression` as | ||
| its body instead of a separate `ifBody` rule. This makes it hard to differentiate different uses of those `blockExpression`s. | ||
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| It should be possible to refactor the grammar to include more specific rules. While not hard, this will still be tedious. Most of the | ||
| `ParserState` mechanism should become obsolete if this is done. | ||
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| #### Problem in Rust (2): Pattern resolution | ||
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| Rust allows to destruct complex objects using pattern matching. | ||
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| ```rust | ||
| // assigns a = 1; b = 2; c = 5; | ||
| let (a, b,.., c) = (1, 2, 3, 4, 5); | ||
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| // assigns d = tuple[0]; f = tuple[n-1] | ||
| let (d,.., f) = tuple; | ||
| ``` | ||
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| The _patterns_ on the left hand side as well as the elements on the right hand side can be nested freely. The _rest_ | ||
| or _etcetera_ pattern `..` is used to skip a number of elements, so that the elements following it match the end part of | ||
| the assigned object. | ||
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| These `let` pattern assignments can be replaced with a sequence of more basic assignments. This is a possible | ||
| problem of this frontend. | ||
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| #### Problem in Rust (3): `return` is optional | ||
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| In Rust, the `return` keyword is optional. If omitted, the last expression evaluated in the function body is used as the | ||
| return value. | ||
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| ```rust | ||
| fn power(base: i32, exponent: i32) -> i32 { | ||
| if exponent == 0 { 1 } // mark this return value? | ||
| else if exponent == 1 { base } // and this one? | ||
| else if exponent % 2 == 0 { | ||
| let square = |i: i32| { i * i }; | ||
| square(power(base, exponent / 2)) // and this one? | ||
| } else { | ||
| base * power(base, exponent - 1) // and this one? | ||
| } | ||
| } | ||
| ``` | ||
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| That raises the question whether to try and mark these more implicit return values, so that the output of this frontend | ||
| would be consistent with others. | ||
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| To determine all possible return values, semantic information about control structures is necessary which may be tedious | ||
| to extract from the AST, but possible (e.g. by means of a stack mechanic). | ||
| On the other hand, "the last expression of a block evaluated" does not hold the same _syntactical_ weight to it as a | ||
| return | ||
| statement. | ||
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| For the moment, implicit block values get no special tokens. | ||
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| #### Problem in Rust (4): Macros | ||
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| Macros are a vital part of Rust. They allow to expand brief statements into more complex, repeating code at compile time. | ||
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| The expansion of the macro arguments into the macro code and the expansion of the macro code itself are purely textual, so a Rust parser does not parse their syntax (apart from the bracket structure). This makes it hard to generate meaningful tokens for them. | ||
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| Currently, macro rule definition bodies and macro macro invocation arguments/bodies get no tokens. | ||
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| ### Usage | ||
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| To use the Rust frontend, add the `-l rust` flag in the CLI, or use a `JPlagOption` object set | ||
| to `LanguageOption.RUST` in the Java API as described in the usage information in | ||
| the [readme of the main project](https://github.com/jplag/JPlag#usage) | ||
| and [in the wiki](https://github.com/jplag/JPlag/wiki/1.-How-to-Use-JPlag). |
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| <?xml version="1.0" encoding="UTF-8"?> | ||
| <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"> | ||
| <modelVersion>4.0.0</modelVersion> | ||
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| <parent> | ||
| <groupId>de.jplag</groupId> | ||
| <artifactId>aggregator</artifactId> | ||
| <version>${revision}</version> | ||
| </parent> | ||
| <artifactId>rust</artifactId> | ||
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| <dependencies> | ||
| <dependency> | ||
| <groupId>org.antlr</groupId> | ||
| <artifactId>antlr4-runtime</artifactId> | ||
| </dependency> | ||
| <dependency> | ||
| <groupId>de.jplag</groupId> | ||
| <artifactId>frontend-utils</artifactId> | ||
| </dependency> | ||
| <dependency> | ||
| <groupId>de.jplag</groupId> | ||
| <artifactId>frontend-testutils</artifactId> | ||
| <version>${revision}</version> | ||
| <type>test-jar</type> | ||
| <scope>test</scope> | ||
| </dependency> | ||
| </dependencies> | ||
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| <build> | ||
| <plugins> | ||
| <plugin> | ||
| <groupId>org.antlr</groupId> | ||
| <artifactId>antlr4-maven-plugin</artifactId> | ||
| <executions> | ||
| <execution> | ||
| <goals> | ||
| <goal>antlr4</goal> | ||
| </goals> | ||
| </execution> | ||
| </executions> | ||
| </plugin> | ||
| </plugins> | ||
| </build> | ||
| </project> |
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jplag.frontend.rust/src/main/antlr4/de/jplag/rust/grammar/README.md
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| # Rust ANTLR 4 grammar | ||
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| This grammar is based on official language reference. | ||
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| Licensed under MIT | ||
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| Entry rule is `crate`. | ||
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| Last updated for rust v1.60.0 | ||
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| ## Maven build | ||
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| Install the parser into the local Maven repository with `mvn install`. | ||
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| ## Known limitation | ||
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| - Only v2018+ stable feature is implemented. | ||
| - Checks about isolated `\r` is not implemented. |
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