AstGen: detect declarations shadowing locals

Closes #9355

lib/std/bounded_array.zig

@@ -15,16 +15,16 @@ const testing = std.testing;
 /// var slice = a.slice(); // a slice of the 64-byte array
 /// var a_clone = a; // creates a copy - the structure doesn't use any internal pointers
 /// ```
-pub fn BoundedArray(comptime T: type, comptime capacity: usize) type {
+pub fn BoundedArray(comptime T: type, comptime buffer_capacity: usize) type {
     return struct {
         const Self = @This();
-        buffer: [capacity]T = undefined,
+        buffer: [buffer_capacity]T = undefined,
         len: usize = 0,
 
         /// Set the actual length of the slice.
         /// Returns error.Overflow if it exceeds the length of the backing array.
         pub fn init(len: usize) error{Overflow}!Self {
-            if (len > capacity) return error.Overflow;
+            if (len > buffer_capacity) return error.Overflow;
             return Self{ .len = len };
         }
 
@@ -41,7 +41,7 @@ pub fn BoundedArray(comptime T: type, comptime capacity: usize) type {
         /// Adjust the slice's length to `len`.
         /// Does not initialize added items if any.
         pub fn resize(self: *Self, len: usize) error{Overflow}!void {
-            if (len > capacity) return error.Overflow;
+            if (len > buffer_capacity) return error.Overflow;
             self.len = len;
         }
 
@@ -69,7 +69,7 @@ pub fn BoundedArray(comptime T: type, comptime capacity: usize) type {
 
         /// Check that the slice can hold at least `additional_count` items.
         pub fn ensureUnusedCapacity(self: Self, additional_count: usize) error{Overflow}!void {
-            if (self.len + additional_count > capacity) {
+            if (self.len + additional_count > buffer_capacity) {
                 return error.Overflow;
             }
         }
@@ -83,7 +83,7 @@ pub fn BoundedArray(comptime T: type, comptime capacity: usize) type {
         /// Increase length by 1, returning pointer to the new item.
         /// Asserts that there is space for the new item.
         pub fn addOneAssumeCapacity(self: *Self) *T {
-            assert(self.len < capacity);
+            assert(self.len < buffer_capacity);
             self.len += 1;
             return &self.slice()[self.len - 1];
         }
@@ -236,7 +236,7 @@ pub fn BoundedArray(comptime T: type, comptime capacity: usize) type {
         pub fn appendNTimesAssumeCapacity(self: *Self, value: T, n: usize) void {
             const old_len = self.len;
             self.len += n;
-            assert(self.len <= capacity);
+            assert(self.len <= buffer_capacity);
             mem.set(T, self.slice()[old_len..self.len], value);
         }
 

lib/std/debug.zig

@@ -1947,7 +1947,7 @@ noinline fn showMyTrace() usize {
 /// For more advanced usage, see `ConfigurableTrace`.
 pub const Trace = ConfigurableTrace(2, 4, builtin.mode == .Debug);
 
-pub fn ConfigurableTrace(comptime size: usize, comptime stack_frame_count: usize, comptime enabled: bool) type {
+pub fn ConfigurableTrace(comptime size: usize, comptime stack_frame_count: usize, comptime is_enabled: bool) type {
     return struct {
         addrs: [actual_size][stack_frame_count]usize = undefined,
         notes: [actual_size][]const u8 = undefined,
@@ -1956,7 +1956,7 @@ pub fn ConfigurableTrace(comptime size: usize, comptime stack_frame_count: usize
         const actual_size = if (enabled) size else 0;
         const Index = if (enabled) usize else u0;
 
-        pub const enabled = enabled;
+        pub const enabled = is_enabled;
 
         pub const add = if (enabled) addNoInline else addNoOp;
 

src/AstGen.zig

@@ -11751,6 +11751,46 @@ fn scanDecls(astgen: *AstGen, namespace: *Scope.Namespace, members: []const Ast.
                 error.OutOfMemory => return error.OutOfMemory,
             }
         }
+
+        // const index_name = try astgen.identAsString(index_token);
+        var s = namespace.parent;
+        while (true) switch (s.tag) {
+            .local_val => {
+                const local_val = s.cast(Scope.LocalVal).?;
+                if (local_val.name == name_str_index) {
+                    return astgen.failTokNotes(name_token, "redeclaration of {s} '{s}'", .{
+                        @tagName(local_val.id_cat), token_bytes,
+                    }, &[_]u32{
+                        try astgen.errNoteTok(
+                            local_val.token_src,
+                            "previous declaration here",
+                            .{},
+                        ),
+                    });
+                }
+                s = local_val.parent;
+            },
+            .local_ptr => {
+                const local_ptr = s.cast(Scope.LocalPtr).?;
+                if (local_ptr.name == name_str_index) {
+                    return astgen.failTokNotes(name_token, "redeclaration of {s} '{s}'", .{
+                        @tagName(local_ptr.id_cat), token_bytes,
+                    }, &[_]u32{
+                        try astgen.errNoteTok(
+                            local_ptr.token_src,
+                            "previous declaration here",
+                            .{},
+                        ),
+                    });
+                }
+                s = local_ptr.parent;
+            },
+            .namespace => s = s.cast(Scope.Namespace).?.parent,
+            .gen_zir => s = s.cast(GenZir).?.parent,
+            .defer_normal, .defer_error => s = s.cast(Scope.Defer).?.parent,
+            .defer_gen => s = s.cast(Scope.DeferGen).?.parent,
+            .top => break,
+        };
         gop.value_ptr.* = member_node;
     }
     return decl_count;

test/cases/compile_errors/decl_shadows_local.zig

@@ -0,0 +1,22 @@
+fn foo(a: usize) void {
+    struct {
+        const a = 1;
+    };
+}
+fn bar(a: usize) void {
+    struct {
+        const b = struct {
+            const a = 1;
+        };
+    };
+    _ = a;
+}
+
+// error
+// backend=stage2
+// target=native
+//
+// :3:15: error: redeclaration of function parameter 'a'
+// :1:8: note: previous declaration here
+// :9:19: error: redeclaration of function parameter 'a'
+// :6:8: note: previous declaration here