cmd/compile: record original and absolute file names for line directives

Also, with this change, error locations don't print absolute positions
in [] brackets following positions relative to line directives. To get
the absolute positions as well, specify the -L flag.

Fixes #22660.

Change-Id: I9ecfa254f053defba9c802222874155fa12fee2c
Reviewed-on: https://go-review.googlesource.com/77090
Reviewed-by: David Crawshaw <crawshaw@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

4 files changed, 7 insertions, 5 deletions

diff --git a/src/cmd/compile/internal/gc/main.go b/src/cmd/compile/internal/gc/main.go
index 6f633a494f..be2fe552f6 100644
--- a/src/cmd/compile/internal/gc/main.go
+++ b/src/cmd/compile/internal/gc/main.go
@@ -192,6 +192,7 @@ func Main(archInit func(*Arch)) {
 	objabi.Flagcount("E", "debug symbol export", &Debug['E'])
 	objabi.Flagfn1("I", "add `directory` to import search path", addidir)
 	objabi.Flagcount("K", "debug missing line numbers", &Debug['K'])
+	objabi.Flagcount("L", "show full file names in error messages", &Debug['L'])
 	objabi.Flagcount("N", "disable optimizations", &Debug['N'])
 	flag.BoolVar(&Debug_asm, "S", false, "print assembly listing")
 	objabi.AddVersionFlag() // -V
diff --git a/src/cmd/compile/internal/gc/subr.go b/src/cmd/compile/internal/gc/subr.go
index b7d530c98c..81441ba700 100644
--- a/src/cmd/compile/internal/gc/subr.go
+++ b/src/cmd/compile/internal/gc/subr.go
@@ -93,7 +93,7 @@ func hcrash() {
 }
 
 func linestr(pos src.XPos) string {
-	return Ctxt.OutermostPos(pos).Format(Debug['C'] == 0)
+	return Ctxt.OutermostPos(pos).Format(Debug['C'] == 0, Debug['L'] == 1)
 }
 
 // lasterror keeps track of the most recently issued error.
diff --git a/src/cmd/compile/internal/syntax/parser.go b/src/cmd/compile/internal/syntax/parser.go
index 7047266a70..ff3e769864 100644
--- a/src/cmd/compile/internal/syntax/parser.go
+++ b/src/cmd/compile/internal/syntax/parser.go
@@ -80,11 +80,12 @@ func (p *parser) updateBase(line, col uint, text string) {
 		p.error_at(p.pos_at(line, col+uint(i+1)), "invalid line number: "+nstr)
 		return
 	}
-	absFile := text[:i]
+	filename := text[:i]
+	absFilename := filename
 	if p.fileh != nil {
-		absFile = p.fileh(absFile)
+		absFilename = p.fileh(filename)
 	}
-	p.base = src.NewLinePragmaBase(src.MakePos(p.base.Pos().Base(), line, col), absFile, uint(n))
+	p.base = src.NewLinePragmaBase(src.MakePos(p.base.Pos().Base(), line, col), filename, absFilename, uint(n))
 }
 
 func (p *parser) got(tok token) bool {
diff --git a/src/cmd/compile/internal/syntax/parser_test.go b/src/cmd/compile/internal/syntax/parser_test.go
index 0478088ec8..309f1333f4 100644
--- a/src/cmd/compile/internal/syntax/parser_test.go
+++ b/src/cmd/compile/internal/syntax/parser_test.go
@@ -221,7 +221,7 @@ func TestLineDirectives(t *testing.T) {
 		if msg := perr.Msg; msg != test.msg {
 			t.Errorf("%s: got msg = %q; want %q", test.src, msg, test.msg)
 		}
-		if filename := perr.Pos.RelFilename(); filename != test.filename {
+		if filename := perr.Pos.AbsFilename(); filename != test.filename {
 			t.Errorf("%s: got filename = %q; want %q", test.src, filename, test.filename)
 		}
 		if line := perr.Pos.RelLine(); line != test.line+linebase {