feat: add --ast CLI argument to emit the AST to stdout

[nturley-copia]

Implements #1003

If the --ast is found, then after Resolve / Annotate, it prints the AST to stdout and then terminates.

Ideally this would be another output format that gets written to disk as JSON or something instead of emitted over stdout, but this is a start.

This just uses the default Rust Debug formatting.

For example:

target\debug\plc.exe examples/hello_world.st --ast

produced

[
    (
        CompilationUnit {
            global_vars: [],
            units: [
                POU {
                    name: "puts",
                    variable_blocks: [
                        VariableBlock {
                            variables: [
                                Variable {
                                    name: "text",
                                    data_type: DataTypeReference {
                                        referenced_type: "STRING",
                                    },
                                },
                            ],
                            variable_block_type: Input(
                                ByRef,
                            ),
                        },
                    ],
                    pou_type: Function,
                    return_type: Some(
                        DataTypeReference {
                            referenced_type: "DINT",
                        },
                    ),
                },
                POU {
                    name: "main",
                    variable_blocks: [],
                    pou_type: Function,
                    return_type: Some(
                        DataTypeReference {
                            referenced_type: "DINT",
                        },
                    ),
                },
            ],
            implementations: [
                Implementation {
                    name: "puts",
                    type_name: "puts",
                    linkage: External,
                    pou_type: Function,
                    statements: [],
                    location: SourceLocation {
                        span: Range(
                            TextLocation {
                                line: 5,
                                column: 0,
                                offset: 75,
                            }..TextLocation {
                                line: 5,
                                column: 12,
                                offset: 87,
                            },
                        ),
                        file: Some(
                            "examples\\hello_world.st",
                        ),
                    },
                    name_location: SourceLocation {
                        span: Range(
                            TextLocation {
                                line: 1,
                                column: 9,
                                offset: 20,
                            }..TextLocation {
                                line: 1,
                                column: 13,
                                offset: 24,
                            },
                        ),
                        file: Some(
                            "examples\\hello_world.st",
                        ),
                    },
                    overriding: false,
                    generic: false,
                    access: None,
                },
                Implementation {
                    name: "main",
                    type_name: "main",
                    linkage: Internal,
                    pou_type: Function,
                    statements: [
                        CallStatement {
                            operator: ReferenceExpr {
                                kind: Member(
                                    Identifier {
                                        name: "puts",
                                    },
                                ),
                                base: None,
                            },
                            parameters: Some(
                                LiteralString {
                                    value: "hello, world!\n",
                                    is_wide: false,
                                },
                            ),
                        },
                    ],
                    location: SourceLocation {
                        span: Range(
                            TextLocation {
                                line: 8,
                                column: 4,
                                offset: 114,
                            }..TextLocation {
                                line: 9,
                                column: 12,
                                offset: 151,
                            },
                        ),
                        file: Some(
                            "examples\\hello_world.st",
                        ),
                    },
                    name_location: SourceLocation {
                        span: Range(
                            TextLocation {
                                line: 7,
                                column: 9,
                                offset: 98,
                            }..TextLocation {
                                line: 7,
                                column: 13,
                                offset: 102,
                            },
                        ),
                        file: Some(
                            "examples\\hello_world.st",
                        ),
                    },
                    overriding: false,
                    generic: false,
                    access: None,
                },
            ],
            user_types: [],
            file_name: "examples\\hello_world.st",
        },
        {
            Datatype(
                "puts",
            ),
            Datatype(
                "STRING",
            ),
            Datatype(
                "main",
            ),
            Datatype(
                "__auto_pointer_to_STRING",
            ),
            Datatype(
                "DINT",
            ),
            Call(
                "puts",
            ),
            Datatype(
                "__STRING_14",
            ),
        },
        StringLiterals {
            utf08: {
                "hello, world!\n",
            },
            utf16: {},
        },
    ),
]

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 91.17%. Comparing base (be78df6) to head (6d419be).
Report is 40 commits behind head on master.

Files	Patch %	Lines
compiler/plc_driver/src/lib.rs	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1256      +/-   ##
==========================================
+ Coverage   91.11%   91.17%   +0.06%     
==========================================
  Files         153      155       +2     
  Lines       44816    45497     +681     
==========================================
+ Hits        40833    41481     +648     
- Misses       3983     4016      +33     

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[volsa]

Looks good, thanks!