implement super basic check

src/main.rs

@@ -1,16 +1,23 @@
 use lexer::Token;
 use logos::Lexer;
 use logos::Logos;
-use syntax::parse;
+use syntax::parse_syntax;
 use utils::ws;
 use winnow::prelude::*;
 use winnow::Parser;
 
+use crate::syntax::check_syntax;
+
 mod lexer;
 mod syntax;
 mod utils;
 
 fn main() {
+    // valid
     let input = "load \"./image.png\" | invert | save \"./image_processed.jpg\"";
-    dbg!(parse(input));
+    dbg!(parse_syntax(input));
+
+    // invalid
+    let invalid_no_streamer = "| invert | save \"./image_processed.jpg\"";
+    check_syntax(parse_syntax(invalid_no_streamer), invalid_no_streamer)
 }

src/syntax.rs

@@ -1,5 +1,14 @@
+use core::panic;
 use std::mem;
 
+use codespan_reporting::diagnostic::Diagnostic;
+use codespan_reporting::diagnostic::Label;
+use codespan_reporting::files::Files;
+use codespan_reporting::files::SimpleFile;
+use codespan_reporting::files::SimpleFiles;
+use codespan_reporting::term;
+use codespan_reporting::term::termcolor::ColorChoice;
+use codespan_reporting::term::termcolor::StandardStream;
 use logos::Logos;
 use logos::Span;
 
@@ -31,7 +40,7 @@ pub enum CommandPartKind {
     String(String),
 }
 
-pub fn parse(input: &str) -> Vec<PipelineElement> {
+pub fn parse_syntax(input: &str) -> Vec<PipelineElement> {
     let lexer = Token::lexer(input);
 
     let mut r = Vec::new();
@@ -76,6 +85,7 @@ pub fn parse(input: &str) -> Vec<PipelineElement> {
                 _ => {}
             }
         } else {
+            panic!("Error at {span:?}")
         }
     }
 
@@ -91,8 +101,31 @@ pub fn parse(input: &str) -> Vec<PipelineElement> {
     r
 }
 
+pub fn check_syntax(syntax: Vec<PipelineElement>, raw_source: &str) {
+    let mut files = SimpleFiles::new();
+    let file_id = files.add("input", raw_source);
+
+    if let Some(PipelineElement {
+        kind: PipelineElementKind::Pipe,
+        span,
+    }) = syntax.first()
+    {
+        let err = Diagnostic::error()
+            .with_message("Missing streamer for pipeline")
+            .with_labels(vec![
+                Label::primary(file_id, 0..span.end).with_message("expected streamer")
+            ])
+            .with_notes(vec!["a pipeline can't start with a pipe".to_string()]);
+
+        let writer = StandardStream::stderr(ColorChoice::Always);
+        let config = codespan_reporting::term::Config::default();
+
+        term::emit(&mut writer.lock(), &config, &files, &err).unwrap();
+    }
+}
+
 #[test]
 fn test_simple_parse_pipeline() {
     let test_pipeline = "load ./image.png | invert | save ./image_processed.jpg";
-    parse(test_pipeline);
+    parse_syntax(test_pipeline);
 }