Improve diagnostics

packages/yew-macro/src/html_tree/html_component.rs

@@ -1,5 +1,6 @@
 use proc_macro2::Span;
 use quote::{quote, quote_spanned, ToTokens};
+use syn::parse::discouraged::Speculative;
 use syn::parse::{Parse, ParseStream};
 use syn::spanned::Spanned;
 use syn::{Token, Type};
@@ -45,7 +46,7 @@ impl Parse for HtmlComponent {
         }
 
         let mut children = HtmlChildrenTree::new();
-        loop {
+        let close = loop {
             if input.is_empty() {
                 return Err(syn::Error::new_spanned(
                     open.to_spanned(),
@@ -54,12 +55,46 @@ impl Parse for HtmlComponent {
             }
 
             if trying_to_close() {
-                break;
+                let cursor = input.cursor();
+                let _ = cursor
+                    .punct()
+                    .and_then(|(_, cursor)| cursor.punct())
+                    .and_then(|(_, cursor)| cursor.ident())
+                    .ok_or_else(|| {
+                        syn::Error::new(Span::call_site(), "expected a valid closing tag (e.g.: </Component>)")
+                    })?;
+
+                let fork = input.fork();
+                let lt = fork.parse::<Token![<]>()?;
+                let div = Some(fork.parse::<Token![/]>()?);
+                let ty = fork.parse::<Type>()?;
+                if ty != open.ty {
+                    fn format_token_stream(ts: impl ToTokens) -> String {
+                        let string = ts.to_token_stream().to_string();
+                        // remove unnecessary spaces
+                        string.replace(' ', "")
+                    }
+                    let open_ty = open.ty;
+                    return Err(syn::Error::new_spanned(
+                        quote!(#open_ty #ty),
+                        format!(
+                            "mismatched closing tags: expected `{}`, found `{}`",
+                            format_token_stream(open_ty),
+                            format_token_stream(ty)
+                        ),
+                    ));
+                } else {
+                    let gt = fork.parse::<Token![>]>()?;
+                    let close = HtmlComponentClose {
+                        tag: TagTokens { lt, div, gt },
+                        ty,
+                    };
+                    input.advance_to(&fork);
+                    break close;
+                }
             }
             children.parse_child(input)?;
-        }
-
-        let close = input.parse::<HtmlComponentClose>()?;
+        };
 
         if !children.is_empty() {
             if let Some(children_prop) = open.props.children() {

packages/yew-macro/tests/html_macro/component-fail.rs

@@ -148,4 +148,34 @@ fn not_expressions() {
     html! { <HtmlInProps header={format!("ending with semi");} /> };
 }
 
+fn mismatch_closing_tags() {
+    pub struct A;
+    impl Component for A {
+        type Message = ();
+        type Properties = ();
+
+        fn create(_ctx: &Context<Self>) -> Self {
+            unimplemented!()
+        }
+        fn view(&self, _ctx: &Context<Self>) -> Html {
+            unimplemented!()
+        }
+    }
+
+    pub struct B;
+    impl Component for B {
+        type Message = ();
+        type Properties = ();
+
+        fn create(_ctx: &Context<Self>) -> Self {
+            unimplemented!()
+        }
+        fn view(&self, _ctx: &Context<Self>) -> Html {
+            unimplemented!()
+        }
+    }
+    let _ = html! { <A></B> };
+    let _ = html! { <A></> };
+}
+
 fn main() {}

packages/yew-macro/tests/html_macro/component-fail.stderr

@@ -386,6 +386,20 @@ error: only an expression may be assigned as a property. Consider removing this
 148 |     html! { <HtmlInProps header={format!("ending with semi");} /> };
     |                                                             ^
 
+error: mismatched closing tags: expected `A`, found `B`
+   --> tests/html_macro/component-fail.rs:177:22
+    |
+177 |     let _ = html! { <A></B> };
+    |                      ^^^^^
+
+error: expected a valid closing tag (e.g.: </Component>)
+   --> tests/html_macro/component-fail.rs:178:13
+    |
+178 |     let _ = html! { <A></> };
+    |             ^^^^^^^^^^^^^^^^
+    |
+    = note: this error originates in the macro `html` (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error[E0425]: cannot find value `blah` in this scope
   --> tests/html_macro/component-fail.rs:82:22
    |

packages/yew-macro/tests/html_macro/generic-component-fail.rs

@@ -40,9 +40,15 @@ where
     }}
 
 fn compile_fail() {
+    #[allow(unused_imports)]
+    use std::path::Path;
+
     html! { <Generic<String>> };
     html! { <Generic<String>></Generic> };
     html! { <Generic<String>></Generic<Vec<String>>> };
+
+    html! { <Generic<String>></Generic<Path>> };
+    html! { <Generic<String>></> };
 }
 
 fn main() {}

packages/yew-macro/tests/html_macro/generic-component-fail.stderr

@@ -1,21 +1,31 @@
 error: this opening tag has no corresponding closing tag
-  --> tests/html_macro/generic-component-fail.rs:43:13
+  --> tests/html_macro/generic-component-fail.rs:46:13
    |
-43 |     html! { <Generic<String>> };
+46 |     html! { <Generic<String>> };
    |             ^^^^^^^^^^^^^^^^^
 
-error[E0107]: missing generics for struct `Generic`
-  --> tests/html_macro/generic-component-fail.rs:44:32
+error: mismatched closing tags: expected `Generic<String>`, found `Generic`
+  --> tests/html_macro/generic-component-fail.rs:47:14
    |
-44 |     html! { <Generic<String>></Generic> };
-   |                                ^^^^^^^ expected 1 generic argument
+47 |     html! { <Generic<String>></Generic> };
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: mismatched closing tags: expected `Generic<String>`, found `Generic<Vec<String>>`
+  --> tests/html_macro/generic-component-fail.rs:48:14
+   |
+48 |     html! { <Generic<String>></Generic<Vec<String>>> };
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: mismatched closing tags: expected `Generic<String>`, found `Generic<Path>`
+  --> tests/html_macro/generic-component-fail.rs:50:14
    |
-note: struct defined here, with 1 generic parameter: `T`
-  --> tests/html_macro/generic-component-fail.rs:4:12
+50 |     html! { <Generic<String>></Generic<Path>> };
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: expected a valid closing tag (e.g.: </Component>)
+  --> tests/html_macro/generic-component-fail.rs:51:5
    |
-4  | pub struct Generic<T> {
-   |            ^^^^^^^ -
-help: add missing generic argument
+51 |     html! { <Generic<String>></> };
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-44 |     html! { <Generic<String>></Generic<T>> };
-   |                                ~~~~~~~~~~
+   = note: this error originates in the macro `html` (in Nightly builds, run with -Z macro-backtrace for more info)