Move misleading_cfg_in_build_script directly into attribute parsing

Author: GuillaumeGomez

compiler/rustc_attr_parsing/src/attributes/cfg.rs

@@ -88,6 +88,24 @@ pub fn parse_cfg_entry<S: Stage>(
     cx: &mut AcceptContext<'_, '_, S>,
     item: &MetaItemOrLitParser,
 ) -> Result<CfgEntry, ErrorGuaranteed> {
+    let entry = parse_cfg_entry_inner(cx, item)?;
+    let mut spans = Vec::new();
+    let total = misleading_cfgs(&entry, &mut spans);
+    if !spans.is_empty() {
+        cx.emit_lint(
+            UNEXPECTED_CFGS,
+            AttributeLintKind::UnexpectedCfgName((name, name_span), value),
+            span,
+        );
+    }
+    Ok(entry)
+}
+
+fn parse_cfg_entry_inner<S: Stage>(
+    cx: &mut AcceptContext<'_, '_, S>,
+    item: &MetaItemOrLitParser,
+) -> Result<CfgEntry, ErrorGuaranteed> {
+
     Ok(match item {
         MetaItemOrLitParser::MetaItemParser(meta) => match meta.args() {
             ArgParser::List(list) => match meta.path().word_sym() {

compiler/rustc_lint/src/misleading_cfg_in_build_script.rs

@@ -203,8 +203,6 @@ const ERROR_MESSAGE: &str = "target-based cfg should be avoided in build scripts
 
 impl EarlyLintPass for MisleadingCfgInBuildScript {
     fn check_attribute(&mut self, cx: &EarlyContext<'_>, attr: &Attribute) {
-        let mut spans = Vec::new();
-        let mut has_unknown = false;
         match attr.name() {
             Some(sym::cfg) if let Some(meta) = attr.meta() => {
                 get_invalid_cfg_attrs(&meta, &mut spans, &mut has_unknown);

compiler/rustc_session/src/parse.rs

@@ -18,7 +18,7 @@ use rustc_feature::{GateIssue, UnstableFeatures, find_feature_issue};
 use rustc_span::edition::Edition;
 use rustc_span::hygiene::ExpnId;
 use rustc_span::source_map::{FilePathMapping, SourceMap};
-use rustc_span::{Span, Symbol, sym};
+use rustc_span::{ErrorGuaranteed, Span, Symbol, sym};
 
 use crate::Session;
 use crate::config::{Cfg, CheckCfg};
@@ -379,3 +379,30 @@ impl ParseSess {
         self.dcx.handle()
     }
 }
+
+pub fn parse_cfg(parser: &mut rustc_parse::Parser<'_>, sess: &rustc_session::Session<'_>, span: Span, tts: TokenStream) -> Result<CfgEntry, ErrorGuaranteed> {
+    let meta = MetaItemOrLitParser::parse_single(
+        &mut parser,
+        ShouldEmit::Nothing,
+        AllowExprMetavar::Yes,
+    )
+    .map_err(|_| diag.emit())?;
+    AttributeParser::parse_single_args(
+        sess,
+        span,
+        span,
+        AttrStyle::Inner,
+        AttrPath { segments: vec![sym::cfg].into_boxed_slice(), span },
+        None,
+        ParsedDescription::Macro,
+        span,
+        cx.current_expansion.lint_node_id,
+        // Doesn't matter what the target actually is here.
+        Target::Crate,
+        Some(cx.ecfg.features),
+        ShouldEmit::Nothing,
+        &meta,
+        parse_cfg_entry,
+        &CFG_TEMPLATE,
+    )
+}