From 990300a0bcde25d002a5958b96d8943acab2731f Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Tue, 16 Apr 2024 18:44:39 -0700
Subject: [PATCH] Add more extensive tests for ParseStream::peek

---
 tests/test_parse_stream.rs | 179 +++++++++++++++++++++++++++++++++++--
 1 file changed, 170 insertions(+), 9 deletions(-)

diff --git a/tests/test_parse_stream.rs b/tests/test_parse_stream.rs
index 6e4a5a505f..11dc1a6630 100644
--- a/tests/test_parse_stream.rs
+++ b/tests/test_parse_stream.rs
@@ -1,14 +1,175 @@
-#![allow(clippy::let_underscore_untyped)]
+#![allow(clippy::items_after_statements, clippy::let_underscore_untyped)]
 
+use proc_macro2::{Delimiter, Group, Punct, Spacing, Span, TokenStream, TokenTree};
+use quote::quote;
 use syn::ext::IdentExt as _;
-use syn::parse::ParseStream;
-use syn::{Ident, Token};
+use syn::parse::{ParseStream, Parser as _, Result};
+use syn::{parenthesized, token, Ident, Lifetime, Token};
 
 #[test]
-fn test_peek() {
-    let _ = |input: ParseStream| {
-        let _ = input.peek(Ident);
-        let _ = input.peek(Ident::peek_any);
-        let _ = input.peek(Token![::]);
-    };
+fn test_peek_punct() {
+    let tokens = quote!(+= + =);
+
+    fn assert(input: ParseStream) -> Result<()> {
+        assert!(input.peek(Token![+]));
+        assert!(input.peek(Token![+=]));
+
+        let _: Token![+] = input.parse()?;
+
+        assert!(input.peek(Token![=]));
+        assert!(!input.peek(Token![==]));
+        assert!(!input.peek(Token![+]));
+
+        let _: Token![=] = input.parse()?;
+
+        assert!(input.peek(Token![+]));
+        assert!(!input.peek(Token![+=]));
+
+        let _: Token![+] = input.parse()?;
+        let _: Token![=] = input.parse()?;
+        Ok(())
+    }
+
+    assert.parse2(tokens).unwrap();
+}
+
+#[test]
+fn test_peek_lifetime() {
+    // 'static ;
+    let tokens = TokenStream::from_iter([
+        TokenTree::Punct(Punct::new('\'', Spacing::Joint)),
+        TokenTree::Ident(Ident::new("static", Span::call_site())),
+        TokenTree::Punct(Punct::new(';', Spacing::Alone)),
+    ]);
+
+    fn assert(input: ParseStream) -> Result<()> {
+        assert!(input.peek(Lifetime));
+        assert!(input.peek2(Token![;]));
+        assert!(!input.peek2(Token![static]));
+
+        let _: Lifetime = input.parse()?;
+
+        assert!(input.peek(Token![;]));
+
+        let _: Token![;] = input.parse()?;
+        Ok(())
+    }
+
+    assert.parse2(tokens).unwrap();
+}
+
+#[test]
+fn test_peek_not_lifetime() {
+    // ' static
+    let tokens = TokenStream::from_iter([
+        TokenTree::Punct(Punct::new('\'', Spacing::Alone)),
+        TokenTree::Ident(Ident::new("static", Span::call_site())),
+    ]);
+
+    fn assert(input: ParseStream) -> Result<()> {
+        assert!(!input.peek(Lifetime));
+        assert!(input.parse::<Option<Punct>>()?.is_none());
+
+        let _: TokenTree = input.parse()?;
+
+        assert!(input.peek(Token![static]));
+
+        let _: Token![static] = input.parse()?;
+        Ok(())
+    }
+
+    assert.parse2(tokens).unwrap();
+}
+
+#[test]
+fn test_peek_ident() {
+    let tokens = quote!(static var);
+
+    fn assert(input: ParseStream) -> Result<()> {
+        assert!(!input.peek(Ident));
+        assert!(input.peek(Ident::peek_any));
+        assert!(input.peek(Token![static]));
+
+        let _: Token![static] = input.parse()?;
+
+        assert!(input.peek(Ident));
+        assert!(input.peek(Ident::peek_any));
+
+        let _: Ident = input.parse()?;
+        Ok(())
+    }
+
+    assert.parse2(tokens).unwrap();
+}
+
+#[test]
+fn test_peek_groups() {
+    // pub ( :: ) «∅ ! = ∅» static
+    let tokens = TokenStream::from_iter([
+        TokenTree::Ident(Ident::new("pub", Span::call_site())),
+        TokenTree::Group(Group::new(
+            Delimiter::Parenthesis,
+            TokenStream::from_iter([
+                TokenTree::Punct(Punct::new(':', Spacing::Joint)),
+                TokenTree::Punct(Punct::new(':', Spacing::Alone)),
+            ]),
+        )),
+        TokenTree::Group(Group::new(
+            Delimiter::None,
+            TokenStream::from_iter([
+                TokenTree::Punct(Punct::new('!', Spacing::Alone)),
+                TokenTree::Punct(Punct::new('=', Spacing::Alone)),
+            ]),
+        )),
+        TokenTree::Ident(Ident::new("static", Span::call_site())),
+    ]);
+
+    fn assert(input: ParseStream) -> Result<()> {
+        assert!(input.peek2(token::Paren));
+        assert!(input.peek3(token::Group));
+        assert!(input.peek3(Token![!]));
+
+        let _: Token![pub] = input.parse()?;
+
+        assert!(input.peek(token::Paren));
+        assert!(!input.peek(Token![::]));
+        assert!(!input.peek2(Token![::]));
+        assert!(input.peek2(Token![!]));
+        assert!(input.peek2(token::Group));
+        assert!(!input.peek3(Token![=])); // FIXME
+        assert!(input.peek3(Token![static])); // FIXME
+
+        let content;
+        parenthesized!(content in input);
+
+        assert!(content.peek(Token![::]));
+        assert!(content.peek2(Token![:]));
+        assert!(!content.peek3(token::Group));
+        assert!(!content.peek3(Token![!]));
+
+        assert!(input.peek(token::Group));
+        assert!(input.peek(Token![!]));
+
+        let _: Token![::] = content.parse()?;
+
+        assert!(input.peek(token::Group));
+        assert!(input.peek(Token![!]));
+        assert!(input.peek2(Token![=]));
+        assert!(!input.peek3(Token![static])); // FIXME
+        assert!(input.peek2(Token![static])); // FIXME
+
+        let _: Token![!] = input.parse()?;
+
+        assert!(input.peek(Token![=]));
+        assert!(input.peek2(Token![static]));
+
+        let _: Token![=] = input.parse()?;
+
+        assert!(input.peek(Token![static]));
+
+        let _: Token![static] = input.parse()?;
+        Ok(())
+    }
+
+    assert.parse2(tokens).unwrap();
 }