1 files changed, 157 insertions, 0 deletions
diff --git a/mingling_cli/src/lints/unnecessary_render_result_creation.rs b/mingling_cli/src/lints/unnecessary_render_result_creation.rs
new file mode 100644
index 0000000..fa6809b
--- /dev/null
+++ b/mingling_cli/src/lints/unnecessary_render_result_creation.rs
@@ -0,0 +1,157 @@
+//! Unnecessary Manual RenderResult Creation
+//!
+//! ## Summary
+//!
+//! Detects `#[renderer]` functions that manually create a `RenderResult` and
+//! manage it via `r_println!(r, ...)` style calls, when they could be simplified
+//! to `#[renderer(buffer)]` which handles the buffer automatically.
+//!
+//! This lint will not trigger if `r` is used outside of `r_println!`,
+//! `r_eprintln!`, `r_print`, `r_eprint`, or `r_append`.
+//!
+//! ## Metadata
+//!
+//! Author: `Weicao-CatilGrass`
+//! Default: `warn`
+
+use crate::linter::mlint_report::{MlintLevel, MlintReport};
+
+pub fn linter(ast: syn::ItemFn, source: &str) -> Vec<MlintReport> {
+    if !has_renderer_attr(&ast) {
+        return vec![];
+    }
+
+    let stmts = &ast.block.stmts;
+    if stmts.len() < 2 {
+        return vec![];
+    }
+
+    let (r_ident, let_idx) = match find_render_result_new(stmts) {
+        Some(pair) => pair,
+        None => return vec![],
+    };
+
+    let r_name = r_ident.to_string();
+    let mut only_print_and_return = true;
+    let mut print_count = 0;
+
+    for stmt in &stmts[let_idx + 1..] {
+        if !check_stmt_usage(stmt, &r_name, &mut print_count) {
+            only_print_and_return = false;
+            break;
+        }
+    }
+
+    if only_print_and_return && print_count > 0 {
+        let span = MlintReport::span_from_syn(&ast.sig, source);
+        vec![MlintReport {
+            file_name: String::new(),
+            source_code: source.to_string(),
+            level: MlintLevel::Warning,
+            lint_code: "unnecessary_render_result_creation".into(),
+            message: format!(
+                "unnecessary manual `RenderResult` creation in `{}`: use `#[renderer(buffer)]` instead",
+                ast.sig.ident,
+            ),
+            spans: vec![span],
+            attached_reports: vec![MlintReport {
+                file_name: String::new(),
+                source_code: String::new(),
+                level: MlintLevel::Help,
+                lint_code: String::new(),
+                message: "change to `#[renderer(buffer)]` and use `r_println!(...)` without the `r` parameter".into(),
+                spans: vec![],
+                attached_reports: vec![],
+                package_id: None,
+                target_name: None,
+                target_kind: None,
+                target_src_path: None,
+            }],
+            package_id: None,
+            target_name: None,
+            target_kind: None,
+            target_src_path: None,
+        }]
+    } else {
+        vec![]
+    }
+}
+
+fn has_renderer_attr(func: &syn::ItemFn) -> bool {
+    func.attrs.iter().any(|a| {
+        if !a.path().is_ident("renderer") {
+            return false;
+        }
+        if let Ok(list) = a.meta.require_list() {
+            let tokens = list.tokens.to_string();
+            if tokens.contains("buffer") {
+                return false;
+            }
+        }
+        true
+    })
+}
+
+fn find_render_result_new(stmts: &[syn::Stmt]) -> Option<(proc_macro2::Ident, usize)> {
+    for (i, stmt) in stmts.iter().enumerate() {
+        if let syn::Stmt::Local(local) = stmt
+            && let Some(init) = &local.init
+            && let syn::Pat::Ident(pat_id) = &local.pat
+            && pat_id.mutability.is_some()
+            && let syn::Expr::Call(call) = &*init.expr
+            && let syn::Expr::Path(expr_path) = call.func.as_ref()
+        {
+            let segs = &expr_path.path.segments;
+            let matches = match segs.len() {
+                2 => segs[0].ident == "RenderResult" && segs[1].ident == "new",
+                3 => {
+                    segs[0].ident == "mingling"
+                        && segs[1].ident == "RenderResult"
+                        && segs[2].ident == "new"
+                }
+                _ => false,
+            };
+            if matches {
+                return Some((pat_id.ident.clone(), i));
+            }
+        }
+    }
+    None
+}
+
+fn check_stmt_usage(stmt: &syn::Stmt, r_name: &str, print_count: &mut usize) -> bool {
+    // return r; → allowed
+    if let syn::Stmt::Expr(expr, _) = stmt
+        && let syn::Expr::Return(ret) = expr
+        && let Some(ret_expr) = &ret.expr
+        && let syn::Expr::Path(p) = ret_expr.as_ref()
+        && p.path.is_ident(r_name)
+    {
+        return true;
+    }
+
+    // r_println!(r, ...) → allowed
+    if let syn::Stmt::Macro(stmt_mac) = stmt {
+        let macro_name = stmt_mac
+            .mac
+            .path
+            .segments
+            .last()
+            .map(|s| s.ident.to_string())
+            .unwrap_or_default();
+        let is_r_macro = matches!(
+            macro_name.as_str(),
+            "r_println" | "r_eprintln" | "r_print" | "r_eprint" | "r_append"
+        );
+        if is_r_macro
+            && let Some(first_arg) = stmt_mac.mac.tokens.clone().into_iter().next()
+            && first_arg.to_string() == *r_name
+        {
+            *print_count += 1;
+            return true;
+        }
+    }
+
+    let s = format!("{stmt:#?}");
+    !s.contains(&format!("\"{r_name}\""))
+}