[PATCH 3/4] kconfig: distinguish between dependencies and visibility in help text

[Thomas Hebb <tommyhebb@gmail.com>]

Kconfig makes a distinction between dependencies (defined by "depends
on" expressions and enclosing "if" blocks) and visibility (which
includes all dependencies, but also includes inline "if" expressions of
individual properties as well as, for prompts, "visible if" expressions
of enclosing menus).

Before bcdedcc1afd6 ("menuconfig: print more info for symbol without
prompts", the "Depends on" lines of a symbol's help text indicated the
visibility of the prompt property they appeared under. After
bcdedcc1afd, there was always only a single "Depends on" line, which
indicated the visibility of the first P_SYMBOL property of the symbol.
Since P_SYMBOLs never have inline if expressions, this was in effect the
same as the dependencies of the menu item that the P_SYMBOL was attached
to.

Neither of these situations accurately conveyed the dependencies of a
symbol--the first because it was actually the visibility, and the second
because it only showed the dependencies from a single definition.

Now that we print a "Depends on" line for every definition (regardless
of whether or not it has a prompt), we can do better: this patch
switches the "Depends on" line for prompts to show the real dependencies
of the corresponding menu item and additionally adds a "Visible if" line
that shows the visibility only if the visibility is different from the
dependencies (which it isn't for most prompts in Linux).

Before:

  Symbol: THUMB2_KERNEL [=n]
  Type  : bool
  Defined with prompt at arch/arm/Kconfig:1417
    Prompt: Compile the kernel in Thumb-2 mode
    Depends on: (CPU_V7 [=y] || CPU_V7M [=n]) && !CPU_V6 [=n] && !CPU_V6K [=n] && !CPU_THUMBONLY [=n]
    Location:
      -> Kernel Features
    Selects: ARM_UNWIND [=n]

After:

   Symbol: THUMB2_KERNEL [=n]
   Type  : bool
   Defined with prompt at arch/arm/Kconfig:1417
     Prompt: Compile the kernel in Thumb-2 mode
     Depends on: (CPU_V7 [=y] || CPU_V7M [=n]) && !CPU_V6 [=n] && !CPU_V6K [=n]
     Visible if: (CPU_V7 [=y] || CPU_V7M [=n]) && !CPU_V6 [=n] && !CPU_V6K [=n] && !CPU_THUMBONLY [=n]
     Location:
       -> Kernel Features
     Selects: ARM_UNWIND [=n]

Signed-off-by: Thomas Hebb <tommyhebb@gmail.com>
---
 scripts/kconfig/expr.c |  3 +--
 scripts/kconfig/expr.h |  1 +
 scripts/kconfig/menu.c | 12 +++++++++++-
 3 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/scripts/kconfig/expr.c b/scripts/kconfig/expr.c
index 8284444cc3fa..849c574a28d5 100644
--- a/scripts/kconfig/expr.c
+++ b/scripts/kconfig/expr.c
@@ -13,7 +13,6 @@
 
 #define DEBUG_EXPR	0
 
-static int expr_eq(struct expr *e1, struct expr *e2);
 static struct expr *expr_eliminate_yn(struct expr *e);
 
 struct expr *expr_alloc_symbol(struct symbol *sym)
@@ -250,7 +249,7 @@ void expr_eliminate_eq(struct expr **ep1, struct expr **ep2)
  * equals some operand in the other (operands do not need to appear in the same
  * order), recursively.
  */
-static int expr_eq(struct expr *e1, struct expr *e2)
+int expr_eq(struct expr *e1, struct expr *e2)
 {
 	int res, old_count;
 
diff --git a/scripts/kconfig/expr.h b/scripts/kconfig/expr.h
index 017843c9a4f4..d0f17bc9c4ef 100644
--- a/scripts/kconfig/expr.h
+++ b/scripts/kconfig/expr.h
@@ -301,6 +301,7 @@ struct expr *expr_alloc_or(struct expr *e1, struct expr *e2);
 struct expr *expr_copy(const struct expr *org);
 void expr_free(struct expr *e);
 void expr_eliminate_eq(struct expr **ep1, struct expr **ep2);
+int expr_eq(struct expr *e1, struct expr *e2);
 tristate expr_calc_value(struct expr *e);
 struct expr *expr_trans_bool(struct expr *e);
 struct expr *expr_eliminate_dups(struct expr *e);
diff --git a/scripts/kconfig/menu.c b/scripts/kconfig/menu.c
index 59fead4b8823..4d0542875d70 100644
--- a/scripts/kconfig/menu.c
+++ b/scripts/kconfig/menu.c
@@ -718,7 +718,17 @@ static void get_prompt_str(struct gstr *r, struct property *prop,
 		   prop->menu->file->name, prop->menu->lineno);
 	str_printf(r, "  Prompt: %s\n", prop->text);
 
-	get_dep_str(r, prop->visible.expr, "  Depends on: ");
+	get_dep_str(r, prop->menu->dep, "  Depends on: ");
+	/* Most prompts in Linux have visibility that exactly matches their
+	 * dependencies. For these, we print only the dependencies to improve
+	 * readability. However, prompts with inline "if" expressions and
+	 * prompts with a parent that has a "visible if" expression have
+	 * differing dependencies and visibility. In these rare cases, we
+	 * print both. */
+	if (!expr_eq(prop->menu->dep, prop->visible.expr)) {
+		get_dep_str(r, prop->visible.expr, "  Visible if: ");
+	}
+
 	menu = prop->menu->parent;
 	for (i = 0; menu != &rootmenu && i < 8; menu = menu->parent) {
 		bool accessible = menu_is_visible(menu);
-- 
2.24.0