3 files changed, 209 insertions, 4 deletions

diff --git a/crates/ide/src/syntax_highlighting/format.rs b/crates/ide/src/syntax_highlighting/format.rs
new file mode 100644
index 000000000..71bde24f0
--- /dev/null
+++ b/crates/ide/src/syntax_highlighting/format.rs
@@ -0,0 +1,78 @@
+//! Syntax highlighting for format macro strings.
+use syntax::{
+    ast::{self, FormatSpecifier, HasFormatSpecifier},
+    AstNode, AstToken, SyntaxElement, SyntaxKind, SyntaxNode, TextRange,
+};
+
+use crate::{syntax_highlighting::HighlightedRangeStack, HighlightTag, HighlightedRange};
+
+#[derive(Default)]
+pub(super) struct FormatStringHighlighter {
+    format_string: Option<SyntaxElement>,
+}
+
+impl FormatStringHighlighter {
+    pub(super) fn check_for_format_string(&mut self, parent: &SyntaxNode) {
+        // Check if macro takes a format string and remember it for highlighting later.
+        // The macros that accept a format string expand to a compiler builtin macros
+        // `format_args` and `format_args_nl`.
+        if let Some(name) = parent
+            .parent()
+            .and_then(ast::MacroCall::cast)
+            .and_then(|mc| mc.path())
+            .and_then(|p| p.segment())
+            .and_then(|s| s.name_ref())
+        {
+            match name.text().as_str() {
+                "format_args" | "format_args_nl" => {
+                    self.format_string = parent
+                        .children_with_tokens()
+                        .filter(|t| t.kind() != SyntaxKind::WHITESPACE)
+                        .nth(1)
+                        .filter(|e| {
+                            ast::String::can_cast(e.kind()) || ast::RawString::can_cast(e.kind())
+                        })
+                }
+                _ => {}
+            }
+        }
+    }
+    pub(super) fn highlight_format_string(
+        &self,
+        range_stack: &mut HighlightedRangeStack,
+        string: &impl HasFormatSpecifier,
+        range: TextRange,
+    ) {
+        if self.format_string.as_ref() == Some(&SyntaxElement::from(string.syntax().clone())) {
+            range_stack.push();
+            string.lex_format_specifier(|piece_range, kind| {
+                if let Some(highlight) = highlight_format_specifier(kind) {
+                    range_stack.add(HighlightedRange {
+                        range: piece_range + range.start(),
+                        highlight: highlight.into(),
+                        binding_hash: None,
+                    });
+                }
+            });
+            range_stack.pop();
+        }
+    }
+}
+
+fn highlight_format_specifier(kind: FormatSpecifier) -> Option<HighlightTag> {
+    Some(match kind {
+        FormatSpecifier::Open
+        | FormatSpecifier::Close
+        | FormatSpecifier::Colon
+        | FormatSpecifier::Fill
+        | FormatSpecifier::Align
+        | FormatSpecifier::Sign
+        | FormatSpecifier::NumberSign
+        | FormatSpecifier::DollarSign
+        | FormatSpecifier::Dot
+        | FormatSpecifier::Asterisk
+        | FormatSpecifier::QuestionMark => HighlightTag::FormatSpecifier,
+        FormatSpecifier::Integer | FormatSpecifier::Zero => HighlightTag::NumericLiteral,
+        FormatSpecifier::Identifier => HighlightTag::Local,
+    })
+}
diff --git a/crates/ide/src/syntax_highlighting/injection.rs b/crates/ide/src/syntax_highlighting/injection.rs
index 43f4e6fea..acd91b26c 100644
--- a/crates/ide/src/syntax_highlighting/injection.rs
+++ b/crates/ide/src/syntax_highlighting/injection.rs
@@ -3,14 +3,12 @@
 use std::{collections::BTreeMap, convert::TryFrom};
 
 use ast::{HasQuotes, HasStringValue};
+use call_info::ActiveParameter;
 use hir::Semantics;
 use itertools::Itertools;
 use syntax::{ast, AstToken, SyntaxNode, SyntaxToken, TextRange, TextSize};
 
-use crate::{
-    call_info::ActiveParameter, Analysis, Highlight, HighlightModifier, HighlightTag,
-    HighlightedRange, RootDatabase,
-};
+use crate::{Analysis, Highlight, HighlightModifier, HighlightTag, HighlightedRange, RootDatabase};
 
 use super::HighlightedRangeStack;
 
diff --git a/crates/ide/src/syntax_highlighting/macro_rules.rs b/crates/ide/src/syntax_highlighting/macro_rules.rs
new file mode 100644
index 000000000..4462af47e
--- /dev/null
+++ b/crates/ide/src/syntax_highlighting/macro_rules.rs
@@ -0,0 +1,129 @@
+//! Syntax highlighting for macro_rules!.
+use syntax::{SyntaxElement, SyntaxKind, SyntaxToken, TextRange, T};
+
+use crate::{HighlightTag, HighlightedRange};
+
+#[derive(Default)]
+pub(super) struct MacroRulesHighlighter {
+    state: Option<MacroMatcherParseState>,
+}
+
+impl MacroRulesHighlighter {
+    pub(super) fn init(&mut self) {
+        self.state = Some(MacroMatcherParseState::default());
+    }
+
+    pub(super) fn advance(&mut self, token: &SyntaxToken) {
+        if let Some(state) = self.state.as_mut() {
+            update_macro_rules_state(state, token);
+        }
+    }
+
+    pub(super) fn highlight(&self, element: SyntaxElement) -> Option<HighlightedRange> {
+        if let Some(state) = self.state.as_ref() {
+            if matches!(state.rule_state, RuleState::Matcher | RuleState::Expander) {
+                if let Some(range) = is_metavariable(element) {
+                    return Some(HighlightedRange {
+                        range,
+                        highlight: HighlightTag::UnresolvedReference.into(),
+                        binding_hash: None,
+                    });
+                }
+            }
+        }
+        None
+    }
+}
+
+struct MacroMatcherParseState {
+    /// Opening and corresponding closing bracket of the matcher or expander of the current rule
+    paren_ty: Option<(SyntaxKind, SyntaxKind)>,
+    paren_level: usize,
+    rule_state: RuleState,
+    /// Whether we are inside the outer `{` `}` macro block that holds the rules
+    in_invoc_body: bool,
+}
+
+impl Default for MacroMatcherParseState {
+    fn default() -> Self {
+        MacroMatcherParseState {
+            paren_ty: None,
+            paren_level: 0,
+            in_invoc_body: false,
+            rule_state: RuleState::None,
+        }
+    }
+}
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum RuleState {
+    Matcher,
+    Expander,
+    Between,
+    None,
+}
+
+impl RuleState {
+    fn transition(&mut self) {
+        *self = match self {
+            RuleState::Matcher => RuleState::Between,
+            RuleState::Expander => RuleState::None,
+            RuleState::Between => RuleState::Expander,
+            RuleState::None => RuleState::Matcher,
+        };
+    }
+}
+
+fn update_macro_rules_state(state: &mut MacroMatcherParseState, tok: &SyntaxToken) {
+    if !state.in_invoc_body {
+        if tok.kind() == T!['{'] {
+            state.in_invoc_body = true;
+        }
+        return;
+    }
+
+    match state.paren_ty {
+        Some((open, close)) => {
+            if tok.kind() == open {
+                state.paren_level += 1;
+            } else if tok.kind() == close {
+                state.paren_level -= 1;
+                if state.paren_level == 0 {
+                    state.rule_state.transition();
+                    state.paren_ty = None;
+                }
+            }
+        }
+        None => {
+            match tok.kind() {
+                T!['('] => {
+                    state.paren_ty = Some((T!['('], T![')']));
+                }
+                T!['{'] => {
+                    state.paren_ty = Some((T!['{'], T!['}']));
+                }
+                T!['['] => {
+                    state.paren_ty = Some((T!['['], T![']']));
+                }
+                _ => (),
+            }
+            if state.paren_ty.is_some() {
+                state.paren_level = 1;
+                state.rule_state.transition();
+            }
+        }
+    }
+}
+
+fn is_metavariable(element: SyntaxElement) -> Option<TextRange> {
+    let tok = element.as_token()?;
+    match tok.kind() {
+        kind if kind == SyntaxKind::IDENT || kind.is_keyword() => {
+            if let Some(_dollar) = tok.prev_token().filter(|t| t.kind() == SyntaxKind::DOLLAR) {
+                return Some(tok.text_range());
+            }
+        }
+        _ => (),
+    };
+    None
+}