Rollup of 8 pull requests

compiler/rustc_errors/src/styled_buffer.rs

@@ -1,39 +1,52 @@
 // Code for creating styled buffers
 
 use crate::snippet::{Style, StyledString};
-use std::iter;
 
 #[derive(Debug)]
 pub struct StyledBuffer {
-    text: Vec<Vec<char>>,
-    styles: Vec<Vec<Style>>,
+    lines: Vec<Vec<StyledChar>>,
+}
+
+#[derive(Debug, Clone)]
+struct StyledChar {
+    chr: char,
+    style: Style,
+}
+
+impl StyledChar {
+    const SPACE: Self = StyledChar::new(' ', Style::NoStyle);
+
+    const fn new(chr: char, style: Style) -> Self {
+        StyledChar { chr, style }
+    }
 }
 
 impl StyledBuffer {
     pub fn new() -> StyledBuffer {
-        StyledBuffer { text: vec![], styles: vec![] }
+        StyledBuffer { lines: vec![] }
     }
 
+    /// Returns content of `StyledBuffer` splitted by lines and line styles
     pub fn render(&self) -> Vec<Vec<StyledString>> {
         // Tabs are assumed to have been replaced by spaces in calling code.
-        debug_assert!(self.text.iter().all(|r| !r.contains(&'\t')));
+        debug_assert!(self.lines.iter().all(|r| !r.iter().any(|sc| sc.chr == '\t')));
 
         let mut output: Vec<Vec<StyledString>> = vec![];
         let mut styled_vec: Vec<StyledString> = vec![];
 
-        for (row, row_style) in iter::zip(&self.text, &self.styles) {
+        for styled_line in &self.lines {
             let mut current_style = Style::NoStyle;
             let mut current_text = String::new();
 
-            for (&c, &s) in iter::zip(row, row_style) {
-                if s != current_style {
+            for sc in styled_line {
+                if sc.style != current_style {
                     if !current_text.is_empty() {
                         styled_vec.push(StyledString { text: current_text, style: current_style });
                     }
-                    current_style = s;
+                    current_style = sc.style;
                     current_text = String::new();
                 }
-                current_text.push(c);
+                current_text.push(sc.chr);
             }
             if !current_text.is_empty() {
                 styled_vec.push(StyledString { text: current_text, style: current_style });
@@ -49,29 +62,25 @@ impl StyledBuffer {
     }
 
     fn ensure_lines(&mut self, line: usize) {
-        while line >= self.text.len() {
-            self.text.push(vec![]);
-            self.styles.push(vec![]);
+        if line >= self.lines.len() {
+            self.lines.resize(line + 1, Vec::new());
         }
     }
 
+    /// Sets `chr` with `style` for given `line`, `col`.
+    /// If `line` does not exist in our buffer, adds empty lines up to the given
+    /// and fills the last line with unstyled whitespace.
     pub fn putc(&mut self, line: usize, col: usize, chr: char, style: Style) {
         self.ensure_lines(line);
-        if col < self.text[line].len() {
-            self.text[line][col] = chr;
-            self.styles[line][col] = style;
-        } else {
-            let mut i = self.text[line].len();
-            while i < col {
-                self.text[line].push(' ');
-                self.styles[line].push(Style::NoStyle);
-                i += 1;
-            }
-            self.text[line].push(chr);
-            self.styles[line].push(style);
+        if col >= self.lines[line].len() {
+            self.lines[line].resize(col + 1, StyledChar::SPACE);
         }
+        self.lines[line][col] = StyledChar::new(chr, style);
     }
 
+    /// Sets `string` with `style` for given `line`, starting from `col`.
+    /// If `line` does not exist in our buffer, adds empty lines up to the given
+    /// and fills the last line with unstyled whitespace.
     pub fn puts(&mut self, line: usize, col: usize, string: &str, style: Style) {
         let mut n = col;
         for c in string.chars() {
@@ -80,32 +89,40 @@ impl StyledBuffer {
         }
     }
 
+    /// For given `line` inserts `string` with `style` before old content of that line,
+    /// adding lines if needed
     pub fn prepend(&mut self, line: usize, string: &str, style: Style) {
         self.ensure_lines(line);
         let string_len = string.chars().count();
 
-        // Push the old content over to make room for new content
-        for _ in 0..string_len {
-            self.styles[line].insert(0, Style::NoStyle);
-            self.text[line].insert(0, ' ');
+        if !self.lines[line].is_empty() {
+            // Push the old content over to make room for new content
+            for _ in 0..string_len {
+                self.lines[line].insert(0, StyledChar::SPACE);
+            }
         }
 
         self.puts(line, 0, string, style);
     }
 
+    /// For given `line` inserts `string` with `style` after old content of that line,
+    /// adding lines if needed
     pub fn append(&mut self, line: usize, string: &str, style: Style) {
-        if line >= self.text.len() {
+        if line >= self.lines.len() {
             self.puts(line, 0, string, style);
         } else {
-            let col = self.text[line].len();
+            let col = self.lines[line].len();
             self.puts(line, col, string, style);
         }
     }
 
     pub fn num_lines(&self) -> usize {
-        self.text.len()
+        self.lines.len()
     }
 
+    /// Set `style` for `line`, `col_start..col_end` range if:
+    /// 1. That line and column range exist in `StyledBuffer`
+    /// 2. `overwrite` is `true` or existing style is `Style::NoStyle` or `Style::Quotation`
     pub fn set_style_range(
         &mut self,
         line: usize,
@@ -119,10 +136,13 @@ impl StyledBuffer {
         }
     }
 
+    /// Set `style` for `line`, `col` if:
+    /// 1. That line and column exist in `StyledBuffer`
+    /// 2. `overwrite` is `true` or existing style is `Style::NoStyle` or `Style::Quotation`
     pub fn set_style(&mut self, line: usize, col: usize, style: Style, overwrite: bool) {
-        if let Some(ref mut line) = self.styles.get_mut(line) {
-            if let Some(s) = line.get_mut(col) {
-                if *s == Style::NoStyle || *s == Style::Quotation || overwrite {
+        if let Some(ref mut line) = self.lines.get_mut(line) {
+            if let Some(StyledChar { style: s, .. }) = line.get_mut(col) {
+                if overwrite || *s == Style::NoStyle || *s == Style::Quotation {
                     *s = style;
                 }
             }

compiler/rustc_hir_pretty/src/lib.rs

@@ -1095,8 +1095,8 @@ impl<'a> State<'a> {
 
     fn print_else(&mut self, els: Option<&hir::Expr<'_>>) {
         match els {
-            Some(_else) => {
-                match _else.kind {
+            Some(else_) => {
+                match else_.kind {
                     // "another else-if"
                     hir::ExprKind::If(ref i, ref then, ref e) => {
                         self.cbox(INDENT_UNIT - 1);
@@ -1114,6 +1114,26 @@ impl<'a> State<'a> {
                         self.s.word(" else ");
                         self.print_block(&b)
                     }
+                    hir::ExprKind::Match(ref expr, arms, _) => {
+                        // else if let desugared to match
+                        assert!(arms.len() == 2, "if let desugars to match with two arms");
+
+                        self.s.word(" else ");
+                        self.s.word("{");
+
+                        self.cbox(INDENT_UNIT);
+                        self.ibox(INDENT_UNIT);
+                        self.word_nbsp("match");
+                        self.print_expr_as_cond(&expr);
+                        self.s.space();
+                        self.bopen();
+                        for arm in arms {
+                            self.print_arm(arm);
+                        }
+                        self.bclose(expr.span);
+
+                        self.s.word("}");
+                    }
                     // BLEAH, constraints would be great here
                     _ => {
                         panic!("print_if saw if with weird alternative");

compiler/rustc_metadata/src/creader.rs

@@ -511,8 +511,11 @@ impl<'a> CrateLoader<'a> {
         if dep.is_none() {
             self.used_extern_options.insert(name);
         }
-        self.maybe_resolve_crate(name, dep_kind, dep)
-            .unwrap_or_else(|err| err.report(self.sess, span))
+        self.maybe_resolve_crate(name, dep_kind, dep).unwrap_or_else(|err| {
+            let missing_core =
+                self.maybe_resolve_crate(sym::core, CrateDepKind::Explicit, None).is_err();
+            err.report(&self.sess, span, missing_core)
+        })
     }
 
     fn maybe_resolve_crate<'b>(

compiler/rustc_metadata/src/locator.rs

@@ -790,7 +790,8 @@ pub fn find_plugin_registrar(
 ) -> (PathBuf, CrateDisambiguator) {
     match find_plugin_registrar_impl(sess, metadata_loader, name) {
         Ok(res) => res,
-        Err(err) => err.report(sess, span),
+        // `core` is always available if we got as far as loading plugins.
+        Err(err) => err.report(sess, span, false),
     }
 }
 
@@ -883,7 +884,7 @@ crate enum CrateError {
 }
 
 impl CrateError {
-    crate fn report(self, sess: &Session, span: Span) -> ! {
+    crate fn report(self, sess: &Session, span: Span, missing_core: bool) -> ! {
         let mut err = match self {
             CrateError::NonAsciiName(crate_name) => sess.struct_span_err(
                 span,
@@ -1068,7 +1069,37 @@ impl CrateError {
                     if (crate_name == sym::std || crate_name == sym::core)
                         && locator.triple != TargetTriple::from_triple(config::host_triple())
                     {
-                        err.note(&format!("the `{}` target may not be installed", locator.triple));
+                        if missing_core {
+                            err.note(&format!(
+                                "the `{}` target may not be installed",
+                                locator.triple
+                            ));
+                        } else {
+                            err.note(&format!(
+                                "the `{}` target may not support the standard library",
+                                locator.triple
+                            ));
+                        }
+                        if missing_core && std::env::var("RUSTUP_HOME").is_ok() {
+                            err.help(&format!(
+                                "consider downloading the target with `rustup target add {}`",
+                                locator.triple
+                            ));
+                        }
+                        // Suggest using #![no_std]. #[no_core] is unstable and not really supported anyway.
+                        // NOTE: this is a dummy span if `extern crate std` was injected by the compiler.
+                        // If it's not a dummy, that means someone added `extern crate std` explicitly and `#![no_std]` won't help.
+                        if !missing_core && span.is_dummy() {
+                            let current_crate =
+                                sess.opts.crate_name.as_deref().unwrap_or("<unknown>");
+                            err.note(&format!(
+                                "`std` is required by `{}` because it does not declare `#![no_std]`",
+                                current_crate
+                            ));
+                        }
+                        if sess.is_nightly_build() && std::env::var("CARGO").is_ok() {
+                            err.help("consider building the standard library from source with `cargo build -Zbuild-std`");
+                        }
                     } else if crate_name == sym::profiler_builtins {
                         err.note(&"the compiler may have been built without the profiler runtime");
                     }

compiler/rustc_middle/src/mir/query.rs

@@ -19,10 +19,8 @@ use super::{Field, SourceInfo};
 
 #[derive(Copy, Clone, PartialEq, TyEncodable, TyDecodable, HashStable, Debug)]
 pub enum UnsafetyViolationKind {
-    /// Only permitted in regular `fn`s, prohibited in `const fn`s.
+    /// Unsafe operation outside `unsafe`.
     General,
-    /// Permitted both in `const fn`s and regular `fn`s.
-    GeneralAndConstFn,
     /// Unsafe operation in an `unsafe fn` but outside an `unsafe` block.
     /// Has to be handled as a lint for backwards compatibility.
     UnsafeFn,

compiler/rustc_mir/src/const_eval/fn_queries.rs

@@ -1,4 +1,3 @@
-use rustc_attr as attr;
 use rustc_hir as hir;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_middle::hir::map::blocks::FnLikeNode;
@@ -34,54 +33,6 @@ pub fn is_unstable_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> Option<Symbol> {
     }
 }
 
-/// Returns `true` if this function must conform to `min_const_fn`
-pub fn is_min_const_fn(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
-    // Bail out if the signature doesn't contain `const`
-    if !tcx.is_const_fn_raw(def_id) {
-        return false;
-    }
-
-    if tcx.features().staged_api {
-        // In order for a libstd function to be considered min_const_fn
-        // it needs to be stable and have no `rustc_const_unstable` attribute.
-        match tcx.lookup_const_stability(def_id) {
-            // `rustc_const_unstable` functions don't need to conform.
-            Some(&attr::ConstStability { ref level, .. }) if level.is_unstable() => false,
-            None => {
-                if let Some(stab) = tcx.lookup_stability(def_id) {
-                    if stab.level.is_stable() {
-                        tcx.sess.delay_span_bug(
-                            tcx.def_span(def_id),
-                            "stable const functions must have either `rustc_const_stable` or \
-                             `rustc_const_unstable` attribute",
-                        );
-                        // While we errored above, because we don't know if we need to conform, we
-                        // err on the "safe" side and require min_const_fn.
-                        true
-                    } else {
-                        // Unstable functions need not conform to min_const_fn.
-                        false
-                    }
-                } else {
-                    // Internal functions are forced to conform to min_const_fn.
-                    // Annotate the internal function with a const stability attribute if
-                    // you need to use unstable features.
-                    // Note: this is an arbitrary choice that does not affect stability or const
-                    // safety or anything, it just changes whether we need to annotate some
-                    // internal functions with `rustc_const_stable` or with `rustc_const_unstable`
-                    true
-                }
-            }
-            // Everything else needs to conform, because it would be callable from
-            // other `min_const_fn` functions.
-            _ => true,
-        }
-    } else {
-        // users enabling the `const_fn` feature gate can do what they want
-        !tcx.features().const_fn
-    }
-}
-
 pub fn is_parent_const_impl_raw(tcx: TyCtxt<'_>, hir_id: hir::HirId) -> bool {
     let parent_id = tcx.hir().get_parent_did(hir_id);
     if !parent_id.is_top_level_module() { is_const_impl_raw(tcx, parent_id) } else { false }