Auto merge of #76256 - tgnottingham:issue-74890, r=nikomatsakis

incr-comp: hash and serialize span end line/column

Hash both the length and the end location (line/column) of a span. If we
hash only the length, for example, then two otherwise equal spans with
different end locations will have the same hash. This can cause a
problem during incremental compilation wherein a previous result for a
query that depends on the end location of a span will be incorrectly
reused when the end location of the span it depends on has changed. A
similar analysis applies if some query depends specifically on the
length of the span, but we only hash the end location. So hash both.

Fix #46744, fix #59954, fix #63161, fix #73640, fix #73967, fix #74890, fix #75900

---

See #74890 for a more in-depth analysis.

I haven't thought about what other problems this root cause could be responsible for. Please let me know if anything springs to mind. I believe the issue has existed since the inception of incremental compilation.

compiler/rustc_span/src/lib.rs

@@ -1894,16 +1894,37 @@ where
             return;
         }
 
+        let (_, line_hi, col_hi) = match ctx.byte_pos_to_line_and_col(span.hi) {
+            Some(pos) => pos,
+            None => {
+                Hash::hash(&TAG_INVALID_SPAN, hasher);
+                span.ctxt.hash_stable(ctx, hasher);
+                return;
+            }
+        };
+
         Hash::hash(&TAG_VALID_SPAN, hasher);
         // We truncate the stable ID hash and line and column numbers. The chances
         // of causing a collision this way should be minimal.
         Hash::hash(&(file_lo.name_hash as u64), hasher);
 
-        let col = (col_lo.0 as u64) & 0xFF;
-        let line = ((line_lo as u64) & 0xFF_FF_FF) << 8;
-        let len = ((span.hi - span.lo).0 as u64) << 32;
-        let line_col_len = col | line | len;
-        Hash::hash(&line_col_len, hasher);
+        // Hash both the length and the end location (line/column) of a span. If we
+        // hash only the length, for example, then two otherwise equal spans with
+        // different end locations will have the same hash. This can cause a problem
+        // during incremental compilation wherein a previous result for a query that
+        // depends on the end location of a span will be incorrectly reused when the
+        // end location of the span it depends on has changed (see issue #74890). A
+        // similar analysis applies if some query depends specifically on the length
+        // of the span, but we only hash the end location. So hash both.
+
+        let col_lo_trunc = (col_lo.0 as u64) & 0xFF;
+        let line_lo_trunc = ((line_lo as u64) & 0xFF_FF_FF) << 8;
+        let col_hi_trunc = (col_hi.0 as u64) & 0xFF << 32;
+        let line_hi_trunc = ((line_hi as u64) & 0xFF_FF_FF) << 40;
+        let col_line = col_lo_trunc | line_lo_trunc | col_hi_trunc | line_hi_trunc;
+        let len = (span.hi - span.lo).0;
+        Hash::hash(&col_line, hasher);
+        Hash::hash(&len, hasher);
         span.ctxt.hash_stable(ctx, hasher);
     }
 }

src/test/run-make/incr-prev-body-beyond-eof/Makefile

@@ -0,0 +1,19 @@
+include ../../run-make-fulldeps/tools.mk
+
+# FIXME https://github.com/rust-lang/rust/issues/78911
+# ignore-32bit wrong/no cross compiler and sometimes we pass wrong gcc args (-m64)
+
+# Tests that we don't ICE during incremental compilation after modifying a
+# function span such that its previous end line exceeds the number of lines
+# in the new file, but its start line/column and length remain the same.
+
+SRC=$(TMPDIR)/src
+INCR=$(TMPDIR)/incr
+
+all:
+	mkdir $(SRC)
+	mkdir $(INCR)
+	cp a.rs $(SRC)/main.rs
+	$(RUSTC) -C incremental=$(INCR) $(SRC)/main.rs
+	cp b.rs $(SRC)/main.rs
+	$(RUSTC) -C incremental=$(INCR) $(SRC)/main.rs

src/test/run-make/incr-prev-body-beyond-eof/a.rs

@@ -0,0 +1,16 @@
+fn main() {
+    // foo must be used.
+    foo();
+}
+
+// For this test to operate correctly, foo's body must start on exactly the same
+// line and column and have the exact same length in bytes in a.rs and b.rs. In
+// a.rs, the body must end on a line number which does not exist in b.rs.
+// Basically, avoid modifying this file, including adding or removing whitespace!
+fn foo() {
+    assert_eq!(1, 1);
+
+
+
+
+}

src/test/run-make/incr-prev-body-beyond-eof/b.rs

@@ -0,0 +1,12 @@
+fn main() {
+    // foo must be used.
+    foo();
+}
+
+// For this test to operate correctly, foo's body must start on exactly the same
+// line and column and have the exact same length in bytes in a.rs and b.rs. In
+// a.rs, the body must end on a line number which does not exist in b.rs.
+// Basically, avoid modifying this file, including adding or removing whitespace!
+fn foo() {
+    assert_eq!(1, 1);////
+}

src/test/run-make/issue-36710/Makefile

@@ -1,5 +1,6 @@
 include ../../run-make-fulldeps/tools.mk
 
+# FIXME https://github.com/rust-lang/rust/issues/78911
 # ignore-32bit wrong/no cross compiler and sometimes we pass wrong gcc args (-m64)
 
 all: foo